diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 3ee77549724..05246284418 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -37,6 +37,12 @@ npx hereby format # Format the code
 ```
 </critical>
 
+If you are writing or testing TS API features (eg, code in _packages/native-preview/src/api/async/api.ts), additionally, you need to run
+```sh
+npx hereby test:api
+```
+which is not run as part of the primary suite.
+
 ## Compiler Features, Fixes, and Tests
 
 When fixing a bug or implementing a new feature, at least one minimal test case should always be added in advance to verify the fix.
diff --git a/Herebyfile.mjs b/Herebyfile.mjs
index eb170f03554..9617c589058 100644
--- a/Herebyfile.mjs
+++ b/Herebyfile.mjs
@@ -577,6 +577,12 @@ export const generateAST = task({
     run: () => $`node --experimental-strip-types --no-warnings ./_scripts/generate.ts`,
 });
 
+export const generateAPI = task({
+    name: "generate:api",
+    description: "Generates API files from internal/api/proto.go and internal/api/session.go.",
+    run: () => $`go -C ./_tools run ./gen-proto ../internal/api/proto.go ../_packages/native-preview/src/api/proto.generated.ts`,
+});
+
 // ── Vendored npm dependencies ───────────────────────────────────
 
 const vendorJsonrpcDir = "_packages/native-preview/vendor/vscode-jsonrpc";
@@ -834,6 +840,7 @@ export const buildAPI = task({
 export const buildAPITests = task({
     name: "build:api:test",
     description: "Builds the @typescript/native-preview JS API tests.",
+    dependencies: [generateEnums, generateAPI],
     run: async () => {
         await $`npm run -w @typescript/native-preview build:test`;
     },
diff --git a/_packages/native-preview/src/api/async/api.ts b/_packages/native-preview/src/api/async/api.ts
index 797171cc11f..09f38832fe3 100644
--- a/_packages/native-preview/src/api/async/api.ts
+++ b/_packages/native-preview/src/api/async/api.ts
@@ -49,26 +49,28 @@ import {
 } from "../path.ts";
 import type {
     CompilerOptions,
-    CompletionInfoResponse,
+    Diagnostic,
     DocumentIdentifier,
     DocumentPosition,
-    ImportAdderActionRequest,
-    ImportSymbolActionRequest,
-    IndexInfoResponse,
-    InitializeResponse,
+    EmitOutputResponse as ProtocolEmitOutputResponse,
+    ImportAdderAction,
+    IntrinsicTypeMethod,
     LSPUpdateSnapshotParams,
     ParsedCommandLine,
-    ProfileResult,
     ProjectReference,
     ProjectResponse,
-    ReadConfigFileResult,
+    ReadConfigFileResponse,
+    SignaturePropertyMethod,
     SignatureResponse,
     SourceFileMetadata,
+    SymbolPropertyMethod,
     SymbolResponse,
+    SymbolsPropertyMethod,
     TextEdit,
     TypeAcquisition,
-    TypePredicateResponse,
+    TypePropertyMethod,
     TypeResponse,
+    TypesPropertyMethod,
     UpdateSnapshotParams,
     UpdateSnapshotResponse,
 } from "../proto.ts";
@@ -96,14 +98,13 @@ import type {
     CompletionInfo,
     CompletionOptions,
     ConditionalType,
-    Diagnostic,
     EmitOutput,
     EmitOutputFile,
     EmitResult,
     FreshableType,
     GetImportEditsForSymbolsOptions,
     IdentifierTypePredicate,
-    ImportAdderAction,
+    ImportAdderAction as APIImportAdderAction,
     IndexedAccessType,
     IndexInfo,
     IndexType,
@@ -132,13 +133,64 @@ import type {
 
 export { documentURIToFileName, fileNameToDocumentURI } from "../path.ts";
 export { CheckFlags, CompletionItemKind, DiagnosticCategory, ElementFlags, EmitOnly, ModifierFlags, ModuleKind, NodeBuilderFlags, ObjectFlags, SignatureFlags, SignatureKind, SymbolFlags, TypeFlags, TypePredicateKind };
-export type { APIOptions, AssertsIdentifierTypePredicate, AssertsThisTypePredicate, BigIntLiteralType, BooleanLiteralType, ClientSocketOptions, ClientSpawnOptions, CompilerOptions, CompletionEntry, CompletionInfo, CompletionOptions, ConditionalType, Diagnostic, DocumentIdentifier, DocumentPosition, EmitOutput, EmitOutputFile, EmitResult, FreshableType, GetImportEditsForSymbolsOptions, IdentifierTypePredicate, ImportAdderAction, IndexedAccessType, IndexInfo, IndexType, InterfaceType, IntersectionType, IntrinsicType, JSDocTagInfo, LiteralType, LSPConnectionOptions, NumberLiteralType, ObjectType, ParsedCommandLine, ProjectReference, ReadConfigFileResult, RequestTiming, SourceFileMetadata, StringLiteralType, StringMappingType, StructuredType, SubstitutionType, TemplateLiteralType, TextEdit, ThisTypePredicate, TimingAccumulators, TimingInfo, TupleType, Type, TypeAcquisition, TypeParameter, TypePredicate, TypePredicateBase, TypeReference, UnionOrIntersectionType, UnionType };
-
-interface EmitOutputResponse {
-    readonly emitSkipped: boolean;
-    readonly diagnostics: readonly Diagnostic[];
-    readonly outputFiles: readonly (EmitOutputFile & { readonly fileName: string; })[];
-}
+export type {
+    APIImportAdderAction as ImportAdderAction,
+    APIOptions,
+    AssertsIdentifierTypePredicate,
+    AssertsThisTypePredicate,
+    BigIntLiteralType,
+    BooleanLiteralType,
+    ClientSocketOptions,
+    ClientSpawnOptions,
+    CompilerOptions,
+    CompletionEntry,
+    CompletionInfo,
+    CompletionOptions,
+    ConditionalType,
+    Diagnostic,
+    DocumentIdentifier,
+    DocumentPosition,
+    EmitOutput,
+    EmitOutputFile,
+    EmitResult,
+    FreshableType,
+    GetImportEditsForSymbolsOptions,
+    IdentifierTypePredicate,
+    IndexedAccessType,
+    IndexInfo,
+    IndexType,
+    InterfaceType,
+    IntersectionType,
+    IntrinsicType,
+    JSDocTagInfo,
+    LiteralType,
+    LSPConnectionOptions,
+    NumberLiteralType,
+    ObjectType,
+    ParsedCommandLine,
+    ProjectReference,
+    ReadConfigFileResponse,
+    RequestTiming,
+    SourceFileMetadata,
+    StringLiteralType,
+    StringMappingType,
+    StructuredType,
+    SubstitutionType,
+    TemplateLiteralType,
+    TextEdit,
+    ThisTypePredicate,
+    TimingAccumulators,
+    TimingInfo,
+    TupleType,
+    Type,
+    TypeAcquisition,
+    TypeParameter,
+    TypePredicate,
+    TypePredicateBase,
+    TypeReference,
+    UnionOrIntersectionType,
+    UnionType,
+};
 
 export interface TranspileOptions {
     compilerOptions?: CompilerOptions;
@@ -172,14 +224,14 @@ export class API<FromLSP extends boolean = false> {
      * Use this when connecting to an API pipe provided by an LSP server via custom/initializeAPISession.
      */
     static async fromLSPConnection(options: LSPConnectionOptions): Promise<API<true>> {
-        const api = new API(options);
+        const api = new API<true>(options);
         await api.ensureInitialized();
         return api;
     }
 
     private async ensureInitialized(): Promise<void> {
         if (!this.initialized) {
-            const response = await this.client.apiRequest<InitializeResponse>("initialize", null);
+            const response = await this.client.apiRequest("initialize", null);
             const getCanonicalFileName = createGetCanonicalFileName(response.useCaseSensitiveFileNames);
             const currentDirectory = response.currentDirectory;
             this.toPath = (fileName: string) => toPath(fileName, currentDirectory, getCanonicalFileName) as Path;
@@ -189,17 +241,17 @@ export class API<FromLSP extends boolean = false> {
 
     async parseConfigFile(file: DocumentIdentifier): Promise<ParsedCommandLine> {
         await this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseConfigFile", { file });
+        return this.client.apiRequest("parseConfigFile", { file });
     }
 
     async parseCommandLine(commandLine: readonly string[]): Promise<ParsedCommandLine> {
         await this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseCommandLine", { commandLine });
+        return this.client.apiRequest("parseCommandLine", { commandLine });
     }
 
-    async readConfigFile(file: DocumentIdentifier): Promise<ReadConfigFileResult> {
+    async readConfigFile(file: DocumentIdentifier): Promise<ReadConfigFileResponse> {
         await this.ensureInitialized();
-        return this.client.apiRequest<ReadConfigFileResult>("readConfigFile", { file });
+        return this.client.apiRequest("readConfigFile", { file });
     }
 
     async parseJsonConfigFileContent(
@@ -209,34 +261,34 @@ export class API<FromLSP extends boolean = false> {
             | { configFileName: DocumentIdentifier; configDirectory?: never; },
     ): Promise<ParsedCommandLine> {
         await this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseJsonConfigFileContent", { json, ...options });
+        return this.client.apiRequest("parseJsonConfigFileContent", { json, ...options });
     }
 
     async transpileModule(input: string, options: TranspileOptions = {}): Promise<TranspileOutput> {
         await this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileModule", { input, options });
+        return this.client.apiRequest("transpileModule", { input, options });
     }
 
     async transpileModuleFromFile(fileName: string, options: TranspileOptions = {}): Promise<TranspileOutput> {
         await this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileModuleFromFile", { fileName, options });
+        return this.client.apiRequest("transpileModuleFromFile", { fileName, options });
     }
 
     async transpileDeclaration(input: string, options: TranspileOptions = {}): Promise<TranspileOutput> {
         await this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileDeclaration", { input, options });
+        return this.client.apiRequest("transpileDeclaration", { input, options });
     }
 
     async transpileDeclarationFromFile(fileName: string, options: TranspileOptions = {}): Promise<TranspileOutput> {
         await this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileDeclarationFromFile", { fileName, options });
+        return this.client.apiRequest("transpileDeclarationFromFile", { fileName, options });
     }
 
     async updateSnapshot(params?: FromLSP extends true ? LSPUpdateSnapshotParams : UpdateSnapshotParams): Promise<Snapshot> {
         await this.ensureInitialized();
 
         const requestParams = toUpdateSnapshotRequest(params);
-        const data = await this.client.apiRequest<UpdateSnapshotResponse>("updateSnapshot", requestParams);
+        const data = await this.client.apiRequest("updateSnapshot", requestParams);
 
         // Retain cached source files from previous snapshot for unchanged files
         if (this.latestSnapshot) {
@@ -288,7 +340,7 @@ export class API<FromLSP extends boolean = false> {
         if (!this.activeSnapshots.has(baseSnapshot) || baseSnapshot.isDisposed()) {
             throw new Error("Cannot run a temporary file update on an inactive snapshot");
         }
-        const data = await this.client.apiRequest<UpdateSnapshotResponse>("updateTemporarySnapshot", { snapshot: baseSnapshot.id, file, newText });
+        const data = await this.client.apiRequest("updateTemporarySnapshot", { snapshot: baseSnapshot.id, file, newText });
 
         // Retain cached source files from the base snapshot for files unchanged by
         // the temporary update. The temporary snapshot is not the latest snapshot, so
@@ -353,13 +405,13 @@ export class InternalAPI {
 
     async stopCPUProfile(): Promise<string> {
         await this.ensureInitialized();
-        const result = await this.client.apiRequest<ProfileResult>("stopCPUProfile", null);
+        const result = await this.client.apiRequest("stopCPUProfile", null);
         return result.file;
     }
 
     async saveHeapProfile(dir: string): Promise<string> {
         await this.ensureInitialized();
-        const result = await this.client.apiRequest<ProfileResult>("saveHeapProfile", { dir });
+        const result = await this.client.apiRequest("saveHeapProfile", { dir });
         return result.file;
     }
 }
@@ -408,7 +460,7 @@ export class Snapshot {
 
     async getDefaultProjectForFile(file: DocumentIdentifier): Promise<Project | undefined> {
         this.ensureNotDisposed();
-        const data = await this.client.apiRequest<ProjectResponse | null>("getDefaultProjectForFile", {
+        const data = await this.client.apiRequest("getDefaultProjectForFile", {
             snapshot: this.id,
             file,
         });
@@ -477,12 +529,12 @@ class SnapshotObjectRegistry {
         this.symbols.clear();
     }
 
-    async fetchSymbol(source: Symbol | Signature | Type, method: string, handle: number | undefined, projectId?: Path): Promise<Symbol> {
+    async fetchSymbol(source: Symbol | Signature | Type, method: SymbolPropertyMethod, handle: number | undefined, projectId: Path): Promise<Symbol> {
         if (!handle) return undefined as unknown as Symbol;
         const cached = this.getSymbol(handle);
         if (cached) return cached;
 
-        const data = await this.client.apiRequest<SymbolResponse | null>(method, {
+        const data = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: projectId,
             objectId: source.id,
@@ -491,7 +543,7 @@ class SnapshotObjectRegistry {
         return this.getOrCreateSymbol(data);
     }
 
-    async fetchSymbols(source: Symbol | Signature | Type, method: string, handles?: readonly number[], projectId?: Path): Promise<readonly Symbol[]> {
+    async fetchSymbols(source: Symbol | Signature | Type, method: SymbolsPropertyMethod, handles: readonly number[] | undefined, projectId: Path): Promise<readonly Symbol[]> {
         if (handles) {
             const result = new Array<Symbol>(handles.length);
             let allCached = true;
@@ -505,7 +557,7 @@ class SnapshotObjectRegistry {
             }
             if (allCached) return result;
         }
-        const symbolData = await this.client.apiRequest<SymbolResponse[] | null>(method, {
+        const symbolData = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: projectId,
             objectId: source.id,
@@ -574,14 +626,14 @@ class ProjectObjectRegistry {
         this.signatures.clear();
     }
 
-    async fetchOptionalType<T extends Type>(source: Symbol | Signature | Type, method: string, handle: number | false | undefined): Promise<T | undefined> {
+    async fetchOptionalType<T extends Type>(source: Symbol | Signature | Type, method: TypePropertyMethod, handle: number | false | undefined): Promise<T | undefined> {
         if (handle !== false) {
             if (!handle) return undefined;
             const cached = this.getType(handle);
             if (cached) return cached as unknown as T;
         }
 
-        const data = await this.client.apiRequest<TypeResponse | null>(method, {
+        const data = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -590,22 +642,22 @@ class ProjectObjectRegistry {
         return this.getOrCreateType(data) as unknown as T;
     }
 
-    async fetchType<T extends Type>(source: Symbol | Signature | Type, method: string, handle: number | false | undefined): Promise<T> {
+    async fetchType<T extends Type>(source: Symbol | Signature | Type, method: TypePropertyMethod, handle: number | false | undefined): Promise<T> {
         const result = await this.fetchOptionalType<T>(source, method, handle);
         if (result === undefined) throw new Error(`${method} returned no type for ${source.constructor.name} ${source.id}`);
         return result;
     }
 
-    async fetchSymbol(source: Symbol | Signature | Type, method: string, handle: number | undefined): Promise<Symbol> {
+    async fetchSymbol(source: Symbol | Signature | Type, method: SymbolPropertyMethod, handle: number | undefined): Promise<Symbol> {
         return this.snapshotRegistry.fetchSymbol(source, method, handle, this.project.id);
     }
 
-    async fetchSignature(source: Symbol | Signature | Type, method: string, handle: number | undefined): Promise<Signature> {
+    async fetchSignature(source: Symbol | Signature | Type, method: SignaturePropertyMethod, handle: number | undefined): Promise<Signature> {
         if (!handle) return undefined as unknown as Signature;
         const cached = this.getSignature(handle);
         if (cached) return cached;
 
-        const data = await this.client.apiRequest<SignatureResponse | null>(method, {
+        const data = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -614,7 +666,7 @@ class ProjectObjectRegistry {
         return this.getOrCreateSignature(data);
     }
 
-    async fetchTypes(source: Symbol | Signature | Type, method: string, handles?: readonly number[]): Promise<readonly Type[]> {
+    async fetchTypes(source: Symbol | Signature | Type, method: TypesPropertyMethod, handles?: readonly number[]): Promise<readonly Type[]> {
         if (handles) {
             const result = new Array<Type>(handles.length);
             let allCached = true;
@@ -628,7 +680,7 @@ class ProjectObjectRegistry {
             }
             if (allCached) return result;
         }
-        const typesData = await this.client.apiRequest<TypeResponse[] | null>(method, {
+        const typesData = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -637,14 +689,14 @@ class ProjectObjectRegistry {
         else return typesData.map(data => this.getOrCreateType(data));
     }
 
-    async fetchSymbols(source: Symbol | Signature | Type, method: string, handles?: readonly number[]): Promise<readonly Symbol[]> {
+    async fetchSymbols(source: Symbol | Signature | Type, method: SymbolsPropertyMethod, handles?: readonly number[]): Promise<readonly Symbol[]> {
         return this.snapshotRegistry.fetchSymbols(source, method, handles, this.project.id);
     }
 
     // getBaseTypes is a checker-level endpoint keyed by `type` (not `objectId`),
     // so it cannot go through fetchTypes. This helper reuses that server method.
     async fetchBaseTypes(source: Type): Promise<readonly Type[]> {
-        const typesData = await this.client.apiRequest<TypeResponse[] | null>("getBaseTypes", {
+        const typesData = await this.client.apiRequest("getBaseTypes", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -654,7 +706,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchPropertiesOfType(source: Type): Promise<readonly Symbol[]> {
-        const data = await this.client.apiRequest<SymbolResponse[] | null>("getPropertiesOfType", {
+        const data = await this.client.apiRequest("getPropertiesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -663,7 +715,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchApparentPropertiesOfType(source: Type): Promise<readonly Symbol[]> {
-        const data = await this.client.apiRequest<SymbolResponse[] | null>("getApparentPropertiesOfType", {
+        const data = await this.client.apiRequest("getApparentPropertiesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -672,7 +724,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchPropertyOfType(source: Type, name: string): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getPropertyOfType", {
+        const data = await this.client.apiRequest("getPropertyOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -682,7 +734,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchSignaturesOfType(source: Type, kind: SignatureKind): Promise<readonly Signature[]> {
-        const data = await this.client.apiRequest<SignatureResponse[]>("getSignaturesOfType", {
+        const data = await this.client.apiRequest("getSignaturesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -692,7 +744,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchIndexInfosOfType(source: Type): Promise<readonly IndexInfo[]> {
-        const data = await this.client.apiRequest<IndexInfoResponse[] | null>("getIndexInfosOfType", {
+        const data = await this.client.apiRequest("getIndexInfosOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -707,7 +759,7 @@ class ProjectObjectRegistry {
     }
 
     async fetchTypeParameterAtPosition(source: Signature, pos: number): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getTypeParameterAtPosition", {
+        const data = await this.client.apiRequest("getTypeParameterAtPosition", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: source.id,
@@ -741,8 +793,11 @@ export class Project {
         toPath: (fileName: string) => Path,
         snapshotRegistry: SnapshotObjectRegistry,
     ) {
-        this.id = data.id;
+        this.id = data.id as Path;
         this.configFileName = data.configFileName;
+        if (!data.parsedCommandLine?.options) {
+            throw new Error(`Project '${data.configFileName}' has no parsed command line`);
+        }
         this.parsedCommandLine = data.parsedCommandLine;
         this.compilerOptions = this.parsedCommandLine.options;
         this.rootFiles = this.parsedCommandLine.fileNames;
@@ -767,7 +822,7 @@ export class Project {
     }
 
     /** @deprecated Use `languageService.getImportAdderEdits`. */
-    getImportAdderEdits(file: DocumentIdentifier, actions: readonly ImportAdderAction[]): Promise<readonly TextEdit[]> {
+    getImportAdderEdits(file: DocumentIdentifier, actions: readonly APIImportAdderAction[]): Promise<readonly TextEdit[]> {
         return this.languageService.getImportAdderEdits(file, actions);
     }
 
@@ -799,11 +854,11 @@ export class LanguageService {
         this.objectRegistry = objectRegistry;
     }
 
-    async getImportAdderEdits(file: DocumentIdentifier, actions: readonly ImportAdderAction[]): Promise<readonly TextEdit[]> {
-        const requestActions: ImportAdderActionRequest[] = actions.map(action => {
+    async getImportAdderEdits(file: DocumentIdentifier, actions: readonly APIImportAdderAction[]): Promise<readonly TextEdit[]> {
+        const requestActions: ImportAdderAction[] = actions.map(action => {
             switch (action.kind) {
                 case "importSymbol":
-                    const importSymbolAction: ImportSymbolActionRequest = {
+                    const importSymbolAction: ImportAdderAction = {
                         kind: "importSymbol",
                         symbol: action.symbol.id,
                     };
@@ -816,7 +871,7 @@ export class LanguageService {
             }
         });
 
-        const data = await this.client.apiRequest<TextEdit[]>("getImportAdderEdits", {
+        const data = await this.client.apiRequest("getImportAdderEdits", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -828,7 +883,7 @@ export class LanguageService {
     async getImportEditsForSymbols(file: DocumentIdentifier, symbols: readonly Symbol[], options: GetImportEditsForSymbolsOptions = {}): Promise<readonly TextEdit[]> {
         return this.getImportAdderEdits(
             file,
-            symbols.map((symbol): ImportAdderAction => {
+            symbols.map((symbol): APIImportAdderAction => {
                 if (options.isValidTypeOnlyUseSite !== undefined) {
                     return {
                         kind: "importSymbol",
@@ -845,7 +900,7 @@ export class LanguageService {
     }
 
     async getReferencedSymbolsForNode(node: Node, position: number): Promise<ReferencedSymbolEntry[]> {
-        const data = await this.client.apiRequest<{ definition: string; symbol?: SymbolResponse; references: string[]; }[] | null>("getReferencedSymbolsForNode", {
+        const data = await this.client.apiRequest("getReferencedSymbolsForNode", {
             snapshot: this.snapshotId,
             project: this.project.id,
             node: getNodeId(node),
@@ -859,7 +914,7 @@ export class LanguageService {
     }
 
     async getSignatureUsage(signatureDecl: Node): Promise<SignatureUsage[]> {
-        const data = await this.client.apiRequest<{ name: string; call?: string; }[] | null>("getSignatureUsages", {
+        const data = await this.client.apiRequest("getSignatureUsages", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signatureDecl: getNodeId(signatureDecl),
@@ -871,13 +926,13 @@ export class LanguageService {
     }
 
     async getCompletionsAtPosition(document: string, position: number, options?: CompletionOptions): Promise<CompletionInfo | undefined> {
-        const data = await this.client.apiRequest<CompletionInfoResponse | null>("getCompletionsAtPosition", {
+        const data = await this.client.apiRequest("getCompletionsAtPosition", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: document,
             position,
-            triggerCharacter: options?.triggerCharacter,
-            includeSymbol: options?.includeSymbol,
+            ...(options?.triggerCharacter !== undefined ? { triggerCharacter: options.triggerCharacter } : {}),
+            ...(options?.includeSymbol !== undefined ? { includeSymbol: options.includeSymbol } : {}),
         });
         if (!data) return undefined;
         return {
@@ -947,7 +1002,7 @@ export class Program {
     }
 
     async getSourceFileNames(): Promise<readonly string[]> {
-        const data = await this.client.apiRequest<string[] | null>("getSourceFileNames", {
+        const data = await this.client.apiRequest("getSourceFileNames", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -979,7 +1034,7 @@ export class Program {
     }
 
     private async fetchSourceFileMetadata(path: Path): Promise<SourceFileMetadata | undefined> {
-        const data = await this.client.apiRequest<SourceFileMetadata | null>("getSourceFileMetadata", {
+        const data = await this.client.apiRequest("getSourceFileMetadata", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: path,
@@ -1012,7 +1067,7 @@ export class Program {
      * Includes the root config file and any extended config files.
      */
     async getConfigFileNames(): Promise<readonly string[]> {
-        const data = await this.client.apiRequest<string[]>("getConfigFileNames", {
+        const data = await this.client.apiRequest("getConfigFileNames", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1037,8 +1092,6 @@ export class Program {
     }
 
     /**
-     * Get syntactic (parse) diagnostics for a specific file or all files.
-     * @param file - Optional file to get diagnostics for. If omitted, returns diagnostics for all files.
      * Get syntactic (parse) diagnostics for specific files or all files.
      * @param file - Optional file(s) to get diagnostics for. If omitted, returns diagnostics for all files.
      */
@@ -1046,10 +1099,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = await this.client.apiRequest<Diagnostic[]>("getSyntacticDiagnostics", {
+        const data = await this.client.apiRequest("getSyntacticDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1062,10 +1115,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = await this.client.apiRequest<Diagnostic[]>("getBindDiagnostics", {
+        const data = await this.client.apiRequest("getBindDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1078,10 +1131,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = await this.client.apiRequest<Diagnostic[]>("getSemanticDiagnostics", {
+        const data = await this.client.apiRequest("getSemanticDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1094,10 +1147,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = await this.client.apiRequest<Diagnostic[]>("getSuggestionDiagnostics", {
+        const data = await this.client.apiRequest("getSuggestionDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1110,10 +1163,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = await this.client.apiRequest<Diagnostic[]>("getDeclarationDiagnostics", {
+        const data = await this.client.apiRequest("getDeclarationDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1122,7 +1175,7 @@ export class Program {
      * Get program-wide diagnostics for the project, including compiler options diagnostics.
      */
     async getProgramDiagnostics(): Promise<readonly Diagnostic[]> {
-        const data = await this.client.apiRequest<Diagnostic[]>("getProgramDiagnostics", {
+        const data = await this.client.apiRequest("getProgramDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1133,7 +1186,7 @@ export class Program {
      * Get global (non-file-specific) semantic diagnostics for the project.
      */
     async getGlobalDiagnostics(): Promise<readonly Diagnostic[]> {
-        const data = await this.client.apiRequest<Diagnostic[]>("getGlobalDiagnostics", {
+        const data = await this.client.apiRequest("getGlobalDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1144,7 +1197,7 @@ export class Program {
      * Get config file parsing diagnostics for the project.
      */
     async getConfigFileParsingDiagnostics(): Promise<readonly Diagnostic[]> {
-        const data = await this.client.apiRequest<Diagnostic[]>("getConfigFileParsingDiagnostics", {
+        const data = await this.client.apiRequest("getConfigFileParsingDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1158,21 +1211,26 @@ export class Program {
      * is written there. Otherwise, the server writes directly to the host filesystem.
      */
     async emit(emitOnly?: EmitOnly): Promise<EmitResult> {
-        return this.client.apiRequest<EmitResult>("emit", {
+        const response = await this.client.apiRequest("emit", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            emitOnly,
+            ...(emitOnly !== undefined ? { emitOnly } : {}),
         });
+        return {
+            emitSkipped: response.emitSkipped,
+            diagnostics: response.diagnostics,
+            emittedFiles: response.emittedFiles,
+        };
     }
 
     /**
      * Emits files and returns their contents without writing to the filesystem.
      */
     async emitToString(emitOnly?: EmitOnly): Promise<EmitOutput> {
-        const response = await this.client.apiRequest<EmitOutputResponse>("emitToString", {
+        const response = await this.client.apiRequest("emitToString", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            emitOnly,
+            ...(emitOnly !== undefined ? { emitOnly } : {}),
         });
         return toEmitOutput(response);
     }
@@ -1181,7 +1239,7 @@ export class Program {
      * Gets JavaScript output for selected files regardless of project `noEmit`, `emitDeclarationOnly`, and `noEmitOnError` settings.
      */
     async getJavaScriptEmit(files: readonly DocumentIdentifier[]): Promise<EmitOutput> {
-        const response = await this.client.apiRequest<EmitOutputResponse>("getJavaScriptEmit", {
+        const response = await this.client.apiRequest("getJavaScriptEmit", {
             snapshot: this.snapshotId,
             project: this.project.id,
             files,
@@ -1193,7 +1251,7 @@ export class Program {
      * Gets declaration output for selected files regardless of project `noEmit`, `declaration`, `emitDeclarationOnly`, and `noEmitOnError` settings.
      */
     async getDeclarationEmit(files: readonly DocumentIdentifier[]): Promise<EmitOutput> {
-        const response = await this.client.apiRequest<EmitOutputResponse>("getDeclarationEmit", {
+        const response = await this.client.apiRequest("getDeclarationEmit", {
             snapshot: this.snapshotId,
             project: this.project.id,
             files,
@@ -1202,7 +1260,7 @@ export class Program {
     }
 }
 
-function toEmitOutput(response: EmitOutputResponse): EmitOutput {
+function toEmitOutput(response: ProtocolEmitOutputResponse): EmitOutput {
     const outputFiles = new Map<string, EmitOutputFile>();
     for (const { fileName, ...outputFile } of response.outputFiles) {
         outputFiles.set(fileName, outputFile);
@@ -1242,14 +1300,14 @@ export class Checker {
     getSymbolAtLocation(nodes: readonly Node[]): Promise<(Symbol | undefined)[]>;
     async getSymbolAtLocation(nodeOrNodes: Node | readonly Node[]): Promise<Symbol | (Symbol | undefined)[] | undefined> {
         if (Array.isArray(nodeOrNodes)) {
-            const data = await this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsAtLocations", {
+            const data = await this.client.apiRequest("getSymbolsAtLocations", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 locations: nodeOrNodes.map(node => getNodeId(node)),
             });
             return data.map(d => d ? this.objectRegistry.getOrCreateSymbol(d) : undefined);
         }
-        const data = await this.client.apiRequest<SymbolResponse | null>("getSymbolAtLocation", {
+        const data = await this.client.apiRequest("getSymbolAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(nodeOrNodes as Node),
@@ -1261,7 +1319,7 @@ export class Checker {
     getSymbolAtPosition(file: DocumentIdentifier, positions: readonly number[]): Promise<(Symbol | undefined)[]>;
     async getSymbolAtPosition(file: DocumentIdentifier, positionOrPositions: number | readonly number[]): Promise<Symbol | (Symbol | undefined)[] | undefined> {
         if (typeof positionOrPositions === "number") {
-            const data = await this.client.apiRequest<SymbolResponse | null>("getSymbolAtPosition", {
+            const data = await this.client.apiRequest("getSymbolAtPosition", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 file,
@@ -1269,7 +1327,7 @@ export class Checker {
             });
             return data ? this.objectRegistry.getOrCreateSymbol(data) : undefined;
         }
-        const data = await this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsAtPositions", {
+        const data = await this.client.apiRequest("getSymbolsAtPositions", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1282,14 +1340,14 @@ export class Checker {
     getSymbolOfSourceFile(files: readonly DocumentIdentifier[]): Promise<(Symbol | undefined)[]>;
     async getSymbolOfSourceFile(fileOrFiles: DocumentIdentifier | readonly DocumentIdentifier[]): Promise<Symbol | (Symbol | undefined)[] | undefined> {
         if (Array.isArray(fileOrFiles)) {
-            const data = await this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsOfSourceFiles", {
+            const data = await this.client.apiRequest("getSymbolsOfSourceFiles", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 files: fileOrFiles,
             });
             return data.map(d => d ? this.objectRegistry.getOrCreateSymbol(d) : undefined);
         }
-        const data = await this.client.apiRequest<SymbolResponse | null>("getSymbolOfSourceFile", {
+        const data = await this.client.apiRequest("getSymbolOfSourceFile", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: fileOrFiles as DocumentIdentifier,
@@ -1306,14 +1364,14 @@ export class Checker {
     getTypeOfSymbol(symbols: readonly Symbol[]): Promise<Type[]>;
     async getTypeOfSymbol(symbolOrSymbols: Symbol | readonly Symbol[]): Promise<Type | Type[]> {
         if (Array.isArray(symbolOrSymbols)) {
-            const data = await this.client.apiRequest<TypeResponse[]>("getTypesOfSymbols", {
+            const data = await this.client.apiRequest("getTypesOfSymbols", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 symbols: symbolOrSymbols.map(s => s.id),
             });
             return data.map(d => this.objectRegistry.getOrCreateType(d));
         }
-        const data = await this.client.apiRequest<TypeResponse>("getTypeOfSymbol", {
+        const data = await this.client.apiRequest("getTypeOfSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: (symbolOrSymbols as Symbol).id,
@@ -1327,7 +1385,7 @@ export class Checker {
      * {@link Type.isErrorType} to detect it).
      */
     async getDeclaredTypeOfSymbol(symbol: Symbol): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getDeclaredTypeOfSymbol", {
+        const data = await this.client.apiRequest("getDeclaredTypeOfSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1336,7 +1394,7 @@ export class Checker {
     }
 
     async getReferencesToSymbolInFile(file: DocumentIdentifier, symbol: Symbol): Promise<NodeHandle[]> {
-        const data = await this.client.apiRequest<string[] | null>("getReferencesToSymbolInFile", {
+        const data = await this.client.apiRequest("getReferencesToSymbolInFile", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1369,14 +1427,14 @@ export class Checker {
     getTypeAtLocation(nodes: readonly Node[]): Promise<Type[]>;
     async getTypeAtLocation(nodeOrNodes: Node | readonly Node[]): Promise<Type | Type[]> {
         if (Array.isArray(nodeOrNodes)) {
-            const data = await this.client.apiRequest<TypeResponse[]>("getTypeAtLocations", {
+            const data = await this.client.apiRequest("getTypeAtLocations", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 locations: nodeOrNodes.map(node => getNodeId(node)),
             });
             return data.map(d => this.objectRegistry.getOrCreateType(d));
         }
-        const data = await this.client.apiRequest<TypeResponse>("getTypeAtLocation", {
+        const data = await this.client.apiRequest("getTypeAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(nodeOrNodes as Node),
@@ -1394,7 +1452,7 @@ export class Checker {
      * signature (use {@link Checker.isUnknownSignature} to detect it).
      */
     async getResolvedSignature(node: Node): Promise<Signature> {
-        const data = await this.client.apiRequest<SignatureResponse>("getResolvedSignature", {
+        const data = await this.client.apiRequest("getResolvedSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1406,7 +1464,7 @@ export class Checker {
     getTypeAtPosition(file: DocumentIdentifier, positions: readonly number[]): Promise<(Type | undefined)[]>;
     async getTypeAtPosition(file: DocumentIdentifier, positionOrPositions: number | readonly number[]): Promise<Type | (Type | undefined)[] | undefined> {
         if (typeof positionOrPositions === "number") {
-            const data = await this.client.apiRequest<TypeResponse | null>("getTypeAtPosition", {
+            const data = await this.client.apiRequest("getTypeAtPosition", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 file,
@@ -1414,7 +1472,7 @@ export class Checker {
             });
             return data ? this.objectRegistry.getOrCreateType(data) : undefined;
         }
-        const data = await this.client.apiRequest<(TypeResponse | null)[]>("getTypesAtPositions", {
+        const data = await this.client.apiRequest("getTypesAtPositions", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1431,15 +1489,19 @@ export class Checker {
     ): Promise<Symbol | undefined> {
         // Distinguish Node (has `kind`) from DocumentPosition (has `document` and `position`)
         const isNode = location && "kind" in location;
-        const data = await this.client.apiRequest<SymbolResponse | null>("resolveName", {
+        const data = await this.client.apiRequest("resolveName", {
             snapshot: this.snapshotId,
             project: this.project.id,
             name,
             meaning,
-            location: isNode ? getNodeId(location as Node) : undefined,
-            file: !isNode && location ? (location as DocumentPosition).document : undefined,
-            position: !isNode && location ? (location as DocumentPosition).position : undefined,
-            excludeGlobals,
+            ...(isNode ? { location: getNodeId(location as Node) } : {}),
+            ...(!isNode && location
+                ? {
+                    file: (location as DocumentPosition).document,
+                    position: (location as DocumentPosition).position,
+                }
+                : {}),
+            ...(excludeGlobals !== undefined ? { excludeGlobals } : {}),
         });
         return data ? this.objectRegistry.getOrCreateSymbol(data) : undefined;
     }
@@ -1450,13 +1512,16 @@ export class Checker {
     async getSymbolsInScope(location: Node | DocumentPosition, meaning: SymbolFlags): Promise<readonly Symbol[]> {
         // Distinguish Node (has `kind`) from DocumentPosition (has `document` and `position`)
         const isNode = "kind" in location;
-        const data = await this.client.apiRequest<SymbolResponse[] | null>("getSymbolsInScope", {
+        const data = await this.client.apiRequest("getSymbolsInScope", {
             snapshot: this.snapshotId,
             project: this.project.id,
             meaning,
-            location: isNode ? getNodeId(location as Node) : undefined,
-            file: isNode ? undefined : (location as DocumentPosition).document,
-            position: isNode ? undefined : (location as DocumentPosition).position,
+            ...(isNode
+                ? { location: getNodeId(location as Node) }
+                : {
+                    file: (location as DocumentPosition).document,
+                    position: (location as DocumentPosition).position,
+                }),
         });
         return data ? data.map(d => this.objectRegistry.getOrCreateSymbol(d)) : [];
     }
@@ -1468,7 +1533,7 @@ export class Checker {
     }
 
     async getContextualType(node: Expression): Promise<Type | undefined> {
-        const data = await this.client.apiRequest<TypeResponse | null>("getContextualType", {
+        const data = await this.client.apiRequest("getContextualType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1478,7 +1543,7 @@ export class Checker {
 
     /** Get the base type of a literal type (e.g. `number` for `42`). Always returns a type. */
     async getBaseTypeOfLiteralType(type: Type): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getBaseTypeOfLiteralType", {
+        const data = await this.client.apiRequest("getBaseTypeOfLiteralType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1497,7 +1562,7 @@ export class Checker {
      * {@link Type.isErrorType} to detect it).
      */
     async getTypeFromTypeNode(node: TypeNode): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getTypeFromTypeNode", {
+        const data = await this.client.apiRequest("getTypeFromTypeNode", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1507,7 +1572,7 @@ export class Checker {
 
     /** Get the widened type. Always returns a type. */
     async getWidenedType(type: Type): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getWidenedType", {
+        const data = await this.client.apiRequest("getWidenedType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1520,7 +1585,7 @@ export class Checker {
      * returns a type; an out-of-range index yields the `any` type.
      */
     async getParameterType(signature: Signature, index: number): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getParameterType", {
+        const data = await this.client.apiRequest("getParameterType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1530,7 +1595,7 @@ export class Checker {
     }
 
     async isArrayLikeType(type: Type): Promise<boolean> {
-        return this.client.apiRequest<boolean>("isArrayLikeType", {
+        return this.client.apiRequest("isArrayLikeType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1538,7 +1603,7 @@ export class Checker {
     }
 
     async isTypeAssignableTo(source: Type, target: Type): Promise<boolean> {
-        return this.client.apiRequest<boolean>("isTypeAssignableTo", {
+        return this.client.apiRequest("isTypeAssignableTo", {
             snapshot: this.snapshotId,
             project: this.project.id,
             source: source.id,
@@ -1547,7 +1612,7 @@ export class Checker {
     }
 
     async getShorthandAssignmentValueSymbol(node: Node): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getShorthandAssignmentValueSymbol", {
+        const data = await this.client.apiRequest("getShorthandAssignmentValueSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1561,7 +1626,7 @@ export class Checker {
      * error type (use {@link Type.isErrorType} to detect it).
      */
     async getTypeOfSymbolAtLocation(symbol: Symbol, location: Node): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getTypeOfSymbolAtLocation", {
+        const data = await this.client.apiRequest("getTypeOfSymbolAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1570,8 +1635,8 @@ export class Checker {
         return this.objectRegistry.getOrCreateType(data);
     }
 
-    private async getIntrinsicType(method: string): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>(method, {
+    private async getIntrinsicType(method: IntrinsicTypeMethod): Promise<Type> {
+        const data = await this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1620,8 +1685,8 @@ export class Checker {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
         if (!binaryData) return undefined;
         return decodeNode(binaryData) as TypeNode;
@@ -1633,25 +1698,27 @@ export class Checker {
             project: this.project.id,
             signature: signature.id,
             kind,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
         if (!binaryData) return undefined;
         return decodeNode(binaryData) as Node;
     }
 
     async typeToString(type: Type, enclosingDeclaration?: Node, flags?: number): Promise<string> {
-        return this.client.apiRequest<string>("typeToString", {
+        const result = await this.client.apiRequest("typeToString", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
+        if (typeof result !== "string") throw new TypeError("typeToString returned a non-string result");
+        return result;
     }
 
     async isContextSensitive(node: Node): Promise<boolean> {
-        return this.client.apiRequest<boolean>("isContextSensitive", {
+        return this.client.apiRequest("isContextSensitive", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1659,7 +1726,7 @@ export class Checker {
     }
 
     async isArrayType(type: Type): Promise<boolean> {
-        return this.client.apiRequest<boolean>("isArrayType", {
+        return this.client.apiRequest("isArrayType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1667,7 +1734,7 @@ export class Checker {
     }
 
     async isTupleType(type: Type): Promise<boolean> {
-        return this.client.apiRequest<boolean>("isTupleType", {
+        return this.client.apiRequest("isTupleType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1684,7 +1751,7 @@ export class Checker {
      * no rest parameter yields the `any` type.
      */
     async getRestTypeOfSignature(signature: Signature): Promise<Type> {
-        const data = await this.client.apiRequest<TypeResponse>("getRestTypeOfSignature", {
+        const data = await this.client.apiRequest("getRestTypeOfSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1693,7 +1760,7 @@ export class Checker {
     }
 
     async getTypePredicateOfSignature(signature: Signature): Promise<TypePredicate | undefined> {
-        const data = await this.client.apiRequest<TypePredicateResponse | null>("getTypePredicateOfSignature", {
+        const data = await this.client.apiRequest("getTypePredicateOfSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1741,7 +1808,7 @@ export class Checker {
     }
 
     async getBaseConstraintOfType(type: Type): Promise<Type | undefined> {
-        const data = await this.client.apiRequest<TypeResponse | null>("getBaseConstraintOfType", {
+        const data = await this.client.apiRequest("getBaseConstraintOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1750,7 +1817,7 @@ export class Checker {
     }
 
     async getPropertyOfType(type: Type, name: string): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getPropertyOfType", {
+        const data = await this.client.apiRequest("getPropertyOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1760,17 +1827,17 @@ export class Checker {
     }
 
     async getConstantValue(node: Node): Promise<string | number | undefined> {
-        const data = await this.client.apiRequest<string | number | null>("getConstantValue", {
+        const data = await this.client.apiRequest("getConstantValue", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
         });
-        return data ?? undefined;
+        return typeof data === "string" || typeof data === "number" ? data : undefined;
     }
 
     /** Get the signature of a function-like declaration. Always returns a signature. */
     async getSignatureFromDeclaration(node: Node): Promise<Signature> {
-        const data = await this.client.apiRequest<SignatureResponse>("getSignatureFromDeclaration", {
+        const data = await this.client.apiRequest("getSignatureFromDeclaration", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1779,7 +1846,7 @@ export class Checker {
     }
 
     async getExportSpecifierLocalTargetSymbol(node: Node): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getExportSpecifierLocalTargetSymbol", {
+        const data = await this.client.apiRequest("getExportSpecifierLocalTargetSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1793,7 +1860,7 @@ export class Checker {
      * {@link Checker.isUnknownSymbol} to detect it).
      */
     async getAliasedSymbol(symbol: Symbol): Promise<Symbol> {
-        const data = await this.client.apiRequest<SymbolResponse>("getAliasedSymbol", {
+        const data = await this.client.apiRequest("getAliasedSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1806,7 +1873,7 @@ export class Checker {
      * (e.g. `"/path/to/module".Namespace.Name`).
      */
     async getFullyQualifiedName(symbol: Symbol): Promise<string> {
-        return this.client.apiRequest<string>("getFullyQualifiedName", {
+        return this.client.apiRequest("getFullyQualifiedName", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1814,7 +1881,7 @@ export class Checker {
     }
 
     async getImmediateAliasedSymbol(symbol: Symbol): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getImmediateAliasedSymbol", {
+        const data = await this.client.apiRequest("getImmediateAliasedSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1829,7 +1896,7 @@ export class Checker {
      * the first call.
      */
     private getWellKnownSymbols(): Promise<{ unknown: number; undefined: number; arguments: number; }> {
-        return this.wellKnownSymbols ??= this.client.apiRequest<{ unknown: number; undefined: number; arguments: number; }>("getWellKnownSymbols", {
+        return this.wellKnownSymbols ??= this.client.apiRequest("getWellKnownSymbols", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1863,7 +1930,7 @@ export class Checker {
      * identity checks against it are local after the first call.
      */
     private getWellKnownSignatures(): Promise<{ unknown: number; }> {
-        return this.wellKnownSignatures ??= this.client.apiRequest<{ unknown: number; }>("getWellKnownSignatures", {
+        return this.wellKnownSignatures ??= this.client.apiRequest("getWellKnownSignatures", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1879,7 +1946,7 @@ export class Checker {
     }
 
     async getExportsOfModule(symbol: Symbol): Promise<readonly Symbol[]> {
-        const data = await this.client.apiRequest<SymbolResponse[] | null>("getExportsOfModule", {
+        const data = await this.client.apiRequest("getExportsOfModule", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1888,7 +1955,7 @@ export class Checker {
     }
 
     async getMemberInModuleExports(symbol: Symbol, name: string): Promise<Symbol | undefined> {
-        const data = await this.client.apiRequest<SymbolResponse | null>("getMemberInModuleExports", {
+        const data = await this.client.apiRequest("getMemberInModuleExports", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1898,7 +1965,7 @@ export class Checker {
     }
 
     async getJsDocTagsOfSymbol(symbol: Symbol): Promise<readonly JSDocTagInfo[]> {
-        const data = await this.client.apiRequest<JSDocTagInfo[] | null>("getJsDocTags", {
+        const data = await this.client.apiRequest("getJsDocTags", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1907,7 +1974,7 @@ export class Checker {
     }
 
     async getDocumentationCommentOfSymbol(symbol: Symbol): Promise<string> {
-        return this.client.apiRequest<string>("getDocumentationComment", {
+        return this.client.apiRequest("getDocumentationComment", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1918,7 +1985,7 @@ export class Checker {
      * Get the type arguments of a type reference (e.g. the `string` in `Array<string>`).
      */
     async getTypeArguments(type: TypeReference): Promise<readonly Type[]> {
-        const data = await this.client.apiRequest<TypeResponse[] | null>("getTypeArguments", {
+        const data = await this.client.apiRequest("getTypeArguments", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1943,9 +2010,11 @@ export class Emitter {
     async printNode(node: Node, options: PrintNodeOptions = {}): Promise<string> {
         const encoded = encodeNode(node);
         const base64 = uint8ArrayToBase64(encoded);
-        return this.client.apiRequest<string>("printNode", {
+        return this.client.apiRequest("printNode", {
             data: base64,
-            ...options,
+            ...(options.preserveSourceNewlines !== undefined ? { preserveSourceNewlines: options.preserveSourceNewlines } : {}),
+            ...(options.neverAsciiEscape !== undefined ? { neverAsciiEscape: options.neverAsciiEscape } : {}),
+            ...(options.terminateUnterminatedLiterals !== undefined ? { terminateUnterminatedLiterals: options.terminateUnterminatedLiterals } : {}),
         });
     }
 }
@@ -1969,7 +2038,7 @@ export class SnapshotInternalAPI {
      * @returns The formatted text of the node, indented for the insertion position.
      */
     async formatNodeForInsertion(node: Node, file: DocumentIdentifier, position: number): Promise<string> {
-        const data = await this.client.apiRequest<ProjectResponse | null>("getDefaultProjectForFile", {
+        const data = await this.client.apiRequest("getDefaultProjectForFile", {
             snapshot: this.snapshotId,
             file,
         });
@@ -1979,7 +2048,7 @@ export class SnapshotInternalAPI {
 
         const encoded = encodeNode(node);
         const base64 = uint8ArrayToBase64(encoded);
-        return this.client.apiRequest<string>("formatNodeForInsertion", {
+        return this.client.apiRequest("formatNodeForInsertion", {
             snapshot: this.snapshotId,
             project: data.id,
             file,
@@ -2067,11 +2136,11 @@ export class Symbol {
         this.objectRegistry = objectRegistry;
 
         this.id = data.id;
-        this.escapedName = data.name;
-        this.name = unescapeLeadingUnderscores(data.name);
+        this.escapedName = data.name as __String;
+        this.name = unescapeLeadingUnderscores(data.name as __String);
         this.flags = data.flags;
         this.checkFlags = data.checkFlags;
-        const canonicalProject = objectRegistry.getProject(data.project);
+        const canonicalProject = objectRegistry.getProject(data.project as Path);
         if (!canonicalProject) {
             throw new Error(`Symbol ${data.id} references unknown canonical project '${data.project}'`);
         }
@@ -2103,7 +2172,7 @@ export class Symbol {
         return this.exportsCache ??= this.fetchSymbolTable("getExportsOfSymbol");
     }
 
-    private async fetchSymbolTable(method: string): Promise<ReadonlyMap<__String, Symbol>> {
+    private async fetchSymbolTable(method: SymbolsPropertyMethod): Promise<ReadonlyMap<__String, Symbol>> {
         const symbols = await this.objectRegistry.fetchSymbols(this, method, undefined, this.canonicalProject.id);
         const table = new Map<__String, Symbol>();
         for (const symbol of symbols) {
@@ -2187,7 +2256,8 @@ class TypeObject implements Type {
         if (data.value != null) {
             // BigInt literal values are serialized as decimal strings (e.g. "-123") because
             // JSON cannot represent bigint. Decode them back into a real bigint here.
-            this.value = (data.flags & TypeFlags.BigIntLiteral) ? BigInt(data.value) : data.value;
+            const value = data.value as string | number | boolean;
+            this.value = (data.flags & TypeFlags.BigIntLiteral) ? BigInt(value as string) : value;
         }
         if (data.intrinsicName !== undefined) this.intrinsicName = data.intrinsicName;
         if (data.isThisType !== undefined) this.isThisType = data.isThisType;
diff --git a/_packages/native-preview/src/api/async/client.ts b/_packages/native-preview/src/api/async/client.ts
index cdcc2343f8e..11eecc0b73b 100644
--- a/_packages/native-preview/src/api/async/client.ts
+++ b/_packages/native-preview/src/api/async/client.ts
@@ -21,6 +21,10 @@ import {
     isSpawnOptions,
     resolveExePath,
 } from "../options.ts";
+import type {
+    APIMethodInfo,
+    SourceFileResponseMethod,
+} from "../proto.ts";
 import {
     combineTimingInfo,
     disabledServerTimingInfo,
@@ -154,7 +158,7 @@ export class Client {
         }
     }
 
-    async apiRequest<T>(method: string, params?: unknown): Promise<T> {
+    async apiRequest<K extends keyof APIMethodInfo>(method: K, params: APIMethodInfo[K]["params"]): Promise<APIMethodInfo[K]["result"]> {
         if (!this.connected) {
             await this.connect();
         }
@@ -162,7 +166,7 @@ export class Client {
             throw new Error("Connection not established");
         }
 
-        const requestType = new RequestType<unknown, T, void>(method);
+        const requestType = new RequestType<unknown, APIMethodInfo[K]["result"], void>(method);
         if (!this.timing) {
             return this.connection.sendRequest(requestType, params);
         }
@@ -186,8 +190,8 @@ export class Client {
         return result;
     }
 
-    async apiRequestBinary(method: string, params?: unknown): Promise<Uint8Array | undefined> {
-        const response = await this.apiRequest<{ data: string; } | null>(method, params);
+    async apiRequestBinary<K extends SourceFileResponseMethod>(method: K, params: APIMethodInfo[K]["params"]): Promise<Uint8Array | undefined> {
+        const response = await this.apiRequest(method, params);
         if (!response) return undefined;
         const buffer = Buffer.from(response.data, "base64");
         return new Uint8Array(buffer.buffer, buffer.byteOffset, buffer.byteLength);
diff --git a/_packages/native-preview/src/api/compilerOptions.ts b/_packages/native-preview/src/api/compilerOptions.ts
deleted file mode 100644
index 8290b43b0d8..00000000000
--- a/_packages/native-preview/src/api/compilerOptions.ts
+++ /dev/null
@@ -1,112 +0,0 @@
-import type { JsxEmit } from "#enums/jsxEmit";
-import type { ModuleDetectionKind } from "#enums/moduleDetectionKind";
-import type { ModuleKind } from "#enums/moduleKind";
-import type { ModuleResolutionKind } from "#enums/moduleResolutionKind";
-import type { NewLineKind } from "#enums/newLineKind";
-import type { ScriptTarget } from "#enums/scriptTarget";
-
-// Keep in sync with compileroptions.go, obviously
-
-export interface CompilerOptions {
-    allowJs?: boolean;
-    allowArbitraryExtensions?: boolean;
-    allowImportingTsExtensions?: boolean;
-    allowNonTsExtensions?: boolean;
-    allowUmdGlobalAccess?: boolean;
-    allowUnreachableCode?: boolean;
-    allowUnusedLabels?: boolean;
-    assumeChangesOnlyAffectDirectDependencies?: boolean;
-    checkJs?: boolean;
-    customConditions?: string[];
-    composite?: boolean;
-    configFilePath?: string;
-    emitDeclarationOnly?: boolean;
-    emitBOM?: boolean;
-    emitDecoratorMetadata?: boolean;
-    declaration?: boolean;
-    declarationDir?: string;
-    declarationMap?: boolean;
-    deduplicatePackages?: boolean;
-    disableSizeLimit?: boolean;
-    disableSourceOfProjectReferenceRedirect?: boolean;
-    disableSolutionSearching?: boolean;
-    disableReferencedProjectLoad?: boolean;
-    erasableSyntaxOnly?: boolean;
-    exactOptionalPropertyTypes?: boolean;
-    experimentalDecorators?: boolean;
-    forceConsistentCasingInFileNames?: boolean;
-    isolatedModules?: boolean;
-    isolatedDeclarations?: boolean;
-    ignoreConfig?: boolean;
-    ignoreDeprecations?: string;
-    importHelpers?: boolean;
-    inlineSourceMap?: boolean;
-    inlineSources?: boolean;
-    init?: boolean;
-    incremental?: boolean;
-    jsx?: JsxEmit;
-    jsxFactory?: string;
-    jsxFragmentFactory?: string;
-    jsxImportSource?: string;
-    lib?: string[];
-    libReplacement?: boolean;
-    locale?: string;
-    mapRoot?: string;
-    module?: ModuleKind;
-    moduleResolution?: ModuleResolutionKind;
-    moduleSuffixes?: string[];
-    moduleDetection?: ModuleDetectionKind;
-    newLine?: NewLineKind;
-    noEmit?: boolean;
-    noCheck?: boolean;
-    noErrorTruncation?: boolean;
-    noFallthroughCasesInSwitch?: boolean;
-    noImplicitAny?: boolean;
-    noImplicitThis?: boolean;
-    noImplicitReturns?: boolean;
-    noEmitHelpers?: boolean;
-    noLib?: boolean;
-    noPropertyAccessFromIndexSignature?: boolean;
-    noUncheckedIndexedAccess?: boolean;
-    noEmitOnError?: boolean;
-    noUnusedLocals?: boolean;
-    noUnusedParameters?: boolean;
-    noResolve?: boolean;
-    noImplicitOverride?: boolean;
-    noUncheckedSideEffectImports?: boolean;
-    outDir?: string;
-    paths?: Record<string, string[]>;
-    preserveConstEnums?: boolean;
-    preserveSymlinks?: boolean;
-    project?: string;
-    resolveJsonModule?: boolean;
-    resolvePackageJsonExports?: boolean;
-    resolvePackageJsonImports?: boolean;
-    removeComments?: boolean;
-    rewriteRelativeImportExtensions?: boolean;
-    reactNamespace?: string;
-    rootDir?: string;
-    rootDirs?: string[];
-    skipLibCheck?: boolean;
-    stableTypeOrdering?: boolean;
-    strict?: boolean;
-    strictBindCallApply?: boolean;
-    strictBuiltinIteratorReturn?: boolean;
-    strictFunctionTypes?: boolean;
-    strictNullChecks?: boolean;
-    strictPropertyInitialization?: boolean;
-    stripInternal?: boolean;
-    skipDefaultLibCheck?: boolean;
-    sourceMap?: boolean;
-    sourceRoot?: string;
-    suppressOutputPathCheck?: boolean;
-    target?: ScriptTarget;
-    traceResolution?: boolean;
-    tsBuildInfoFile?: string;
-    typeRoots?: string[];
-    types?: string[];
-    useDefineForClassFields?: boolean;
-    useUnknownInCatchVariables?: boolean;
-    verbatimModuleSyntax?: boolean;
-    maxNodeModuleJsDepth?: number;
-}
diff --git a/_packages/native-preview/src/api/proto.generated.ts b/_packages/native-preview/src/api/proto.generated.ts
new file mode 100644
index 00000000000..5e30d12bae2
--- /dev/null
+++ b/_packages/native-preview/src/api/proto.generated.ts
@@ -0,0 +1,1054 @@
+// Code generated by gen-proto; DO NOT EDIT.
+
+import type { JsxEmit } from "#enums/jsxEmit";
+import type { ModuleDetectionKind } from "#enums/moduleDetectionKind";
+import type { ModuleKind } from "#enums/moduleKind";
+import type { ModuleResolutionKind } from "#enums/moduleResolutionKind";
+import type { NewLineKind } from "#enums/newLineKind";
+import type { ScriptTarget } from "#enums/scriptTarget";
+
+export type APIMethod<TParams, TResult> = { params: TParams; result: TResult; };
+
+export interface APIMethodInfo {
+    release: APIMethod<ReleaseParams, void>;
+    initialize: APIMethod<null, InitializeResponse>;
+    updateSnapshot: APIMethod<UpdateSnapshotParams, UpdateSnapshotResponse>;
+    updateTemporarySnapshot: APIMethod<UpdateTemporarySnapshotParams, UpdateSnapshotResponse>;
+    parseCommandLine: APIMethod<ParseCommandLineParams, ConfigFileResponse>;
+    readConfigFile: APIMethod<ReadConfigFileParams, ReadConfigFileResponse>;
+    parseJsonConfigFileContent: APIMethod<ParseJsonConfigFileContentParams, ConfigFileResponse>;
+    parseConfigFile: APIMethod<ParseConfigFileParams, ConfigFileResponse>;
+    transpileModule: APIMethod<TranspileParams, TranspileOutputResponse>;
+    transpileModuleFromFile: APIMethod<TranspileFromFileParams, TranspileOutputResponse>;
+    transpileDeclaration: APIMethod<TranspileParams, TranspileOutputResponse>;
+    transpileDeclarationFromFile: APIMethod<TranspileFromFileParams, TranspileOutputResponse>;
+    getDefaultProjectForFile: APIMethod<GetDefaultProjectForFileParams, ProjectResponse | null>;
+    getSymbolAtPosition: APIMethod<GetSymbolAtPositionParams, SymbolResponse | null>;
+    getSymbolsAtPositions: APIMethod<GetSymbolsAtPositionsParams, SymbolResponse[]>;
+    getSymbolAtLocation: APIMethod<GetSymbolAtLocationParams, SymbolResponse | null>;
+    getSymbolsAtLocations: APIMethod<GetSymbolsAtLocationsParams, SymbolResponse[]>;
+    getSymbolOfSourceFile: APIMethod<GetSymbolOfSourceFileParams, SymbolResponse | null>;
+    getSymbolsOfSourceFiles: APIMethod<GetSymbolsOfSourceFilesParams, SymbolResponse[]>;
+    getTypeOfSymbol: APIMethod<GetTypeOfSymbolParams, TypeResponse>;
+    getTypesOfSymbols: APIMethod<GetTypesOfSymbolsParams, TypeResponse[]>;
+    getDeclaredTypeOfSymbol: APIMethod<GetTypeOfSymbolParams, TypeResponse>;
+    getSourceFile: APIMethod<GetSourceFileParams, SourceFileResponse | null>;
+    getSourceFileNames: APIMethod<GetSourceFileNamesParams, string[]>;
+    getSourceFileMetadata: APIMethod<GetSourceFileParams, SourceFileMetadata | null>;
+    getConfigFileNames: APIMethod<GetProjectDiagnosticsParams, string[] | null>;
+    getConfigSourceFile: APIMethod<GetSourceFileParams, SourceFileResponse | null>;
+    resolveName: APIMethod<ResolveNameParams, SymbolResponse | null>;
+    getSymbolsInScope: APIMethod<GetSymbolsInScopeParams, SymbolResponse[]>;
+    getSignaturesOfType: APIMethod<GetSignaturesOfTypeParams, SignatureResponse[]>;
+    getResolvedSignature: APIMethod<GetResolvedSignatureParams, SignatureResponse>;
+    getTypeAtLocation: APIMethod<GetTypeAtLocationParams, TypeResponse>;
+    getTypeAtLocations: APIMethod<GetTypeAtLocationsParams, TypeResponse[]>;
+    getTypeAtPosition: APIMethod<GetTypeAtPositionParams, TypeResponse | null>;
+    getTypesAtPositions: APIMethod<GetTypesAtPositionsParams, TypeResponse[]>;
+    getParentOfSymbol: APIMethod<GetSymbolPropertyParams, SymbolResponse | null>;
+    getMembersOfSymbol: APIMethod<GetSymbolPropertyParams, SymbolResponse[] | null>;
+    getExportsOfSymbol: APIMethod<GetSymbolPropertyParams, SymbolResponse[] | null>;
+    getExportSymbolOfSymbol: APIMethod<GetSymbolPropertyParams, SymbolResponse | null>;
+    getSymbolOfType: APIMethod<GetTypePropertyParams, SymbolResponse | null>;
+    getTargetOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getFreshTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse | null>;
+    getRegularTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse | null>;
+    getTypesOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;
+    getTypeParametersOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;
+    getOuterTypeParametersOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;
+    getLocalTypeParametersOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;
+    getAliasTypeArgumentsOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;
+    getAliasSymbolOfType: APIMethod<GetTypePropertyParams, SymbolResponse | null>;
+    getObjectTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getIndexTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getCheckTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getExtendsTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getBaseTypeOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getConstraintOfType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getTypeParametersOfSignature: APIMethod<GetSignaturePropertyParams, TypeResponse[] | null>;
+    getParametersOfSignature: APIMethod<GetSignaturePropertyParams, SymbolResponse[] | null>;
+    getThisParameterOfSignature: APIMethod<GetSignaturePropertyParams, SymbolResponse | null>;
+    getTargetOfSignature: APIMethod<GetSignaturePropertyParams, SignatureResponse | null>;
+    getContextualType: APIMethod<GetContextualTypeParams, TypeResponse | null>;
+    getBaseTypeOfLiteralType: APIMethod<GetBaseTypeOfLiteralTypeParams, TypeResponse>;
+    getNonNullableType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getTypeFromTypeNode: APIMethod<GetTypeFromTypeNodeParams, TypeResponse>;
+    getWidenedType: APIMethod<GetWidenedTypeParams, TypeResponse>;
+    getParameterType: APIMethod<GetParameterTypeParams, TypeResponse>;
+    getTypeParameterAtPosition: APIMethod<GetParameterTypeParams, TypeResponse>;
+    isArrayLikeType: APIMethod<IsArrayLikeTypeParams, boolean>;
+    isTypeAssignableTo: APIMethod<IsTypeAssignableToParams, boolean>;
+    getShorthandAssignmentValueSymbol: APIMethod<GetTypeAtLocationParams, SymbolResponse | null>;
+    getTypeOfSymbolAtLocation: APIMethod<GetTypeOfSymbolAtLocationParams, TypeResponse>;
+    typeToTypeNode: APIMethod<TypeToTypeNodeParams, SourceFileResponse | null>;
+    signatureToSignatureDeclaration: APIMethod<SignatureToSignatureDeclarationParams, SourceFileResponse | null>;
+    typeToString: APIMethod<TypeToTypeNodeParams, unknown>;
+    isContextSensitive: APIMethod<GetContextualTypeParams, boolean>;
+    getReturnTypeOfSignature: APIMethod<GetSignaturePropertyParams, TypeResponse>;
+    getRestTypeOfSignature: APIMethod<CheckerSignatureParams, TypeResponse>;
+    getTypePredicateOfSignature: APIMethod<CheckerSignatureParams, TypePredicateResponse | null>;
+    getBaseTypes: APIMethod<CheckerTypeParams, TypeResponse[] | null>;
+    getPropertiesOfType: APIMethod<CheckerTypeParams, SymbolResponse[] | null>;
+    getApparentPropertiesOfType: APIMethod<GetTypePropertyParams, SymbolResponse[]>;
+    getApparentType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getPropertyOfType: APIMethod<GetPropertyOfTypeParams, SymbolResponse | null>;
+    getIndexInfosOfType: APIMethod<CheckerTypeParams, IndexInfoResponse[] | null>;
+    getConstraintOfTypeParameter: APIMethod<GetTypePropertyParams, TypeResponse | null>;
+    getDefaultFromTypeParameter: APIMethod<GetTypePropertyParams, TypeResponse | null>;
+    getBaseConstraintOfType: APIMethod<CheckerTypeParams, TypeResponse | null>;
+    getTypeArguments: APIMethod<CheckerTypeParams, TypeResponse[] | null>;
+    getImportAdderEdits: APIMethod<GetImportAdderEditsParams, TextEdit[]>;
+    getTrueTypeOfConditionalType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getFalseTypeOfConditionalType: APIMethod<GetTypePropertyParams, TypeResponse>;
+    getConstantValue: APIMethod<CheckerNodeParams, unknown | null>;
+    getSignatureFromDeclaration: APIMethod<CheckerNodeParams, SignatureResponse>;
+    getExportSpecifierLocalTargetSymbol: APIMethod<CheckerNodeParams, SymbolResponse | null>;
+    getAliasedSymbol: APIMethod<CheckerSymbolParams, SymbolResponse>;
+    getImmediateAliasedSymbol: APIMethod<CheckerSymbolParams, SymbolResponse | null>;
+    getFullyQualifiedName: APIMethod<CheckerSymbolParams, string>;
+    getExportsOfModule: APIMethod<CheckerSymbolParams, SymbolResponse[] | null>;
+    getMemberInModuleExports: APIMethod<GetMemberInModuleExportsParams, SymbolResponse | null>;
+    getJsDocTags: APIMethod<CheckerSymbolParams, JSDocTagInfo[] | null>;
+    getDocumentationComment: APIMethod<CheckerSymbolParams, string>;
+    isArrayType: APIMethod<CheckerTypeParams, boolean>;
+    isTupleType: APIMethod<CheckerTypeParams, boolean>;
+    getReferencesToSymbolInFile: APIMethod<GetReferencesToSymbolInFileParams, string[]>;
+    getReferencedSymbolsForNode: APIMethod<GetReferencedSymbolsForNodeParams, ReferencedSymbolEntry[] | null>;
+    getSignatureUsages: APIMethod<GetSignatureUsagesParams, SignatureUsageResponse[] | null>;
+    getCompletionsAtPosition: APIMethod<GetCompletionsAtPositionParams, CompletionInfoResponse | null>;
+    getSyntacticDiagnostics: APIMethod<GetDiagnosticsParams, DiagnosticResponse[] | null>;
+    getBindDiagnostics: APIMethod<GetDiagnosticsParams, DiagnosticResponse[] | null>;
+    getSemanticDiagnostics: APIMethod<GetDiagnosticsParams, DiagnosticResponse[] | null>;
+    getSuggestionDiagnostics: APIMethod<GetDiagnosticsParams, DiagnosticResponse[] | null>;
+    getDeclarationDiagnostics: APIMethod<GetDiagnosticsParams, DiagnosticResponse[] | null>;
+    getProgramDiagnostics: APIMethod<GetProjectDiagnosticsParams, DiagnosticResponse[] | null>;
+    getGlobalDiagnostics: APIMethod<GetProjectDiagnosticsParams, DiagnosticResponse[] | null>;
+    getConfigFileParsingDiagnostics: APIMethod<GetProjectDiagnosticsParams, DiagnosticResponse[] | null>;
+    printNode: APIMethod<PrintNodeParams, string>;
+    formatNodeForInsertion: APIMethod<FormatNodeForInsertionParams, string>;
+    emit: APIMethod<EmitParams, EmitResponse>;
+    emitToString: APIMethod<EmitParams, EmitOutputResponse>;
+    getJavaScriptEmit: APIMethod<SelectedFilesEmitParams, EmitOutputResponse>;
+    getDeclarationEmit: APIMethod<SelectedFilesEmitParams, EmitOutputResponse>;
+    getAnyType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getStringType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getNumberType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getBooleanType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getVoidType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getUndefinedType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getNullType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getNeverType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getUnknownType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getBigIntType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getESSymbolType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getNonPrimitiveType: APIMethod<GetIntrinsicTypeParams, TypeResponse>;
+    getWellKnownSymbols: APIMethod<GetIntrinsicTypeParams, WellKnownSymbolsResponse>;
+    getWellKnownSignatures: APIMethod<GetIntrinsicTypeParams, WellKnownSignaturesResponse>;
+    startCPUProfile: APIMethod<ProfileParams, void>;
+    stopCPUProfile: APIMethod<null, ProfileResult>;
+    saveHeapProfile: APIMethod<ProfileParams, ProfileResult>;
+}
+
+export type DocumentIdentifier = string | { uri: string; };
+
+/** ReleaseParams are the parameters for the release method. */
+export interface ReleaseParams {
+    snapshot: number;
+}
+
+/** InitializeResponse is returned by the initialize method. */
+export interface InitializeResponse {
+    /** UseCaseSensitiveFileNames indicates whether the host file system is case-sensitive. */
+    useCaseSensitiveFileNames: boolean;
+    /** CurrentDirectory is the server's current working directory. */
+    currentDirectory: string;
+}
+
+/**
+ * UpdateSnapshotParams are the parameters for creating a new snapshot.
+ * All fields are optional. With no fields set, the server adopts the latest LSP state.
+ */
+export interface UpdateSnapshotParams {
+    /**
+     * OpenProjects lists tsconfig.json files to open/load in the new snapshot.
+     * Opens are ref-counted and persist across snapshots until closed.
+     */
+    openProjects?: readonly DocumentIdentifier[];
+    /**
+     * CloseProjects lists tsconfig.json files to release in the new snapshot.
+     * A project is only unloaded once every API client that opened it closes it.
+     */
+    closeProjects?: readonly DocumentIdentifier[];
+    /** FileChanges describes file system changes since the last snapshot. */
+    fileChanges?: APIFileChanges;
+    /**
+     * OpenFiles lists files to keep open for the API client, mirroring LSP's
+     * textDocument/didOpen. For each file, ancestor directories are searched for a
+     * tsconfig that contains it; if found, that configured project is loaded and
+     * becomes the file's default project. Otherwise the file is loaded into the
+     * inferred project (e.g. a node_modules d.ts not in any project's import graph).
+     * Opens persist across snapshots until the file is closed.
+     */
+    openFiles?: readonly DocumentIdentifier[];
+    /**
+     * CloseFiles lists files to release in the new snapshot. A file is only fully
+     * closed once every API client that opened it closes it.
+     */
+    closeFiles?: readonly DocumentIdentifier[];
+}
+
+/** UpdateSnapshotResponse is returned by updateSnapshot. */
+export interface UpdateSnapshotResponse {
+    /** Snapshot is the handle for the newly created snapshot. */
+    snapshot: number;
+    /** Projects is the list of projects in the snapshot. */
+    projects: ProjectResponse[];
+    /**
+     * Changes describes source file differences from the previous snapshot.
+     * Nil for the first snapshot in a session.
+     */
+    changes?: SnapshotChanges;
+}
+
+/**
+ * UpdateTemporarySnapshotParams are the parameters for creating a temporary
+ * snapshot that overrides a single file's content.
+ */
+export interface UpdateTemporarySnapshotParams {
+    /** Snapshot is the current client snapshot on which to layer the temporary update. */
+    snapshot: number;
+    /** File identifies the file whose content is temporarily overridden. */
+    file: DocumentIdentifier;
+    /** NewText is the temporary content for the file. */
+    newText: string;
+}
+
+export interface ParseCommandLineParams {
+    commandLine: readonly string[] | null;
+}
+
+export interface ConfigFileResponse {
+    fileNames: string[];
+    options: CompilerOptions;
+    projectReferences?: ProjectReference[];
+    typeAcquisition?: TypeAcquisition;
+    compileOnSave?: boolean;
+    raw?: unknown;
+    errors: DiagnosticResponse[];
+}
+
+export interface ReadConfigFileParams {
+    file: DocumentIdentifier;
+}
+
+export interface ReadConfigFileResponse {
+    config: unknown;
+    error?: DiagnosticResponse;
+}
+
+export interface ParseJsonConfigFileContentParams {
+    json: unknown;
+    configDirectory?: string;
+    configFileName?: DocumentIdentifier;
+}
+
+export interface ParseConfigFileParams {
+    file: DocumentIdentifier;
+}
+
+export interface TranspileParams {
+    input: string;
+    options: TranspileOptions;
+}
+
+export interface TranspileOutputResponse {
+    outputText: string;
+    diagnostics?: DiagnosticResponse[];
+    sourceMapText?: string;
+}
+
+export interface TranspileFromFileParams {
+    fileName: string;
+    options: TranspileOptions;
+}
+
+export interface GetDefaultProjectForFileParams {
+    snapshot: number;
+    file: DocumentIdentifier;
+}
+
+export interface ProjectResponse {
+    id: string;
+    configFileName: string;
+    parsedCommandLine: ConfigFileResponse;
+    /** @deprecated Use parsedCommandLine.fileNames. */
+    rootFiles: string[];
+    /** @deprecated Use parsedCommandLine.options. */
+    compilerOptions: CompilerOptions;
+}
+
+export interface GetSymbolAtPositionParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    position: number;
+}
+
+export interface SymbolResponse {
+    id: number;
+    /**
+     * Project is the project in which the symbol was first observed. It is the
+     * default project for follow-up lookups whose results can vary by project.
+     */
+    project: string;
+    name: string;
+    flags: number;
+    checkFlags: number;
+    declarations?: string[];
+    valueDeclaration?: string;
+    parent?: number;
+    exportSymbol?: number;
+}
+
+export interface GetSymbolsAtPositionsParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    positions: readonly number[] | null;
+}
+
+export interface GetSymbolAtLocationParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+export interface GetSymbolsAtLocationsParams {
+    snapshot: number;
+    project: string;
+    locations: readonly string[] | null;
+}
+
+export interface GetSymbolOfSourceFileParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+}
+
+export interface GetSymbolsOfSourceFilesParams {
+    snapshot: number;
+    project: string;
+    files: readonly DocumentIdentifier[] | null;
+}
+
+export interface GetTypeOfSymbolParams {
+    snapshot: number;
+    project: string;
+    symbol: number;
+}
+
+export interface TypeResponse {
+    id: number;
+    flags: number;
+    objectFlags?: number;
+    /**
+     * Value is literal type data. BigInt literals are encoded as signed decimal
+     * strings because JSON cannot represent bigint; absent values are null.
+     */
+    value: unknown;
+    /** ObjectType / TypeReference / StringMappingType / IndexType target */
+    target?: number;
+    /** InterfaceType type parameters */
+    typeParameters?: number[];
+    outerTypeParameters?: number[];
+    localTypeParameters?: number[];
+    /** TupleType data */
+    elementFlags?: number[];
+    fixedLength?: number;
+    readonly?: boolean;
+    /** IndexedAccessType data */
+    objectType?: number;
+    indexType?: number;
+    /** ConditionalType data */
+    checkType?: number;
+    extendsType?: number;
+    /** SubstitutionType data */
+    baseType?: number;
+    substConstraint?: number;
+    /** TemplateLiteralType text segments */
+    texts?: string[];
+    /** FreshableType data (LiteralType and computed enum types) */
+    freshType?: number;
+    regularType?: number;
+    /** TypeParameter data */
+    isThisType?: boolean;
+    /** IntrinsicType data */
+    intrinsicName?: string;
+    /** TypeAlias data */
+    aliasTypeArguments?: number[];
+    aliasSymbol?: number;
+    /** Symbol associated with structured types */
+    symbol?: number;
+}
+
+export interface GetTypesOfSymbolsParams {
+    snapshot: number;
+    project: string;
+    symbols: readonly number[] | null;
+}
+
+export interface GetSourceFileParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+}
+
+/**
+ * SourceFileResponse contains the binary-encoded AST data for a source file.
+ * The Data field is base64-encoded binary data in the encoder's format.
+ */
+export interface SourceFileResponse {
+    /** Data is the base64-encoded binary AST data in the encoder's format. */
+    data: string;
+}
+
+export interface GetSourceFileNamesParams {
+    snapshot: number;
+    project: string;
+}
+
+/** SourceFileMetadata carries program-stored metadata about a single source file. */
+export interface SourceFileMetadata {
+    isDefaultLibrary: boolean;
+    isFromExternalLibrary: boolean;
+    packageJsonType: string;
+    packageJsonDirectory: string;
+    impliedNodeFormat: ModuleKind;
+}
+
+/** GetProjectDiagnosticsParams are parameters for project-wide diagnostic methods. */
+export interface GetProjectDiagnosticsParams {
+    snapshot: number;
+    project: string;
+}
+
+export interface ResolveNameParams {
+    snapshot: number;
+    project: string;
+    name: string;
+    /** Optional: node handle for location context */
+    location?: string;
+    /** Optional: file for location context (alternative to Location) */
+    file?: DocumentIdentifier;
+    /** Optional: position in file for location context (with File) */
+    position?: number;
+    /** SymbolFlags for what kind of symbol to find */
+    meaning: number;
+    /** Whether to exclude global symbols */
+    excludeGlobals?: boolean;
+}
+
+/**
+ * GetSymbolsInScopeParams are parameters for getSymbolsInScope, which returns
+ * all symbols visible at a given location.
+ */
+export interface GetSymbolsInScopeParams {
+    snapshot: number;
+    project: string;
+    /** Optional: node handle for location context */
+    location?: string;
+    /** Optional: file for location context (alternative to Location) */
+    file?: DocumentIdentifier;
+    /** Optional: position in file for location context (with File) */
+    position?: number;
+    /** SymbolFlags for what kind of symbols to find */
+    meaning: number;
+}
+
+export interface GetSignaturesOfTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+    kind: number;
+}
+
+export interface SignatureResponse {
+    id: number;
+    flags: number;
+    declaration?: string;
+    typeParameters?: number[];
+    parameters?: number[];
+    thisParameter?: number;
+    target?: number;
+}
+
+export interface GetResolvedSignatureParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+export interface GetTypeAtLocationParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+export interface GetTypeAtLocationsParams {
+    snapshot: number;
+    project: string;
+    locations: readonly string[] | null;
+}
+
+export interface GetTypeAtPositionParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    position: number;
+}
+
+export interface GetTypesAtPositionsParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    positions: readonly number[] | null;
+}
+
+/** GetSymbolPropertyParams is used for all symbol sub-property endpoints. */
+export interface GetSymbolPropertyParams {
+    snapshot: number;
+    project: string;
+    objectId: number;
+}
+
+/** GetTypePropertyParams is used for all type sub-property endpoints. */
+export interface GetTypePropertyParams {
+    snapshot: number;
+    project: string;
+    objectId: number;
+}
+
+/** GetSignaturePropertyParams is used for all signature sub-property endpoints. */
+export interface GetSignaturePropertyParams {
+    snapshot: number;
+    project: string;
+    objectId: number;
+}
+
+/** GetContextualTypeParams returns the contextual type for a node. */
+export interface GetContextualTypeParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+/** GetBaseTypeOfLiteralTypeParams returns the base type of a literal type. */
+export interface GetBaseTypeOfLiteralTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+}
+
+/** GetTypeFromTypeNodeParams are the parameters for the getTypeFromTypeNode method. */
+export interface GetTypeFromTypeNodeParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+/** GetWidenedTypeParams are the parameters for the getWidenedType method. */
+export interface GetWidenedTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+}
+
+/** GetParameterTypeParams are the parameters for the getParameterType method. */
+export interface GetParameterTypeParams {
+    snapshot: number;
+    project: string;
+    signature: number;
+    index: number;
+}
+
+/** IsArrayLikeTypeParams checks whether a type is array-like. */
+export interface IsArrayLikeTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+}
+
+/** IsTypeAssignableToParams checks assignability between two types. */
+export interface IsTypeAssignableToParams {
+    snapshot: number;
+    project: string;
+    source: number;
+    target: number;
+}
+
+/** GetTypeOfSymbolAtLocationParams returns the narrowed type of a symbol at a specific location. */
+export interface GetTypeOfSymbolAtLocationParams {
+    snapshot: number;
+    project: string;
+    symbol: number;
+    location: string;
+}
+
+/** TypeToTypeNodeParams are the parameters for the typeToTypeNode method. */
+export interface TypeToTypeNodeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+    location?: string;
+    flags?: number;
+}
+
+/** SignatureToSignatureDeclarationParams are the parameters for the signatureToSignatureDeclaration method. */
+export interface SignatureToSignatureDeclarationParams {
+    snapshot: number;
+    project: string;
+    signature: number;
+    kind: number;
+    location?: string;
+    flags?: number;
+}
+
+/** CheckerSignatureParams are parameters for checker methods that operate on a signature. */
+export interface CheckerSignatureParams {
+    snapshot: number;
+    project: string;
+    signature: number;
+}
+
+/** TypePredicateResponse is the response for getTypePredicateOfSignature. */
+export interface TypePredicateResponse {
+    kind: number;
+    parameterIndex: number;
+    parameterName?: string;
+    type?: TypeResponse;
+}
+
+/** CheckerTypeParams are parameters for checker methods that operate on a type. */
+export interface CheckerTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+}
+
+/** GetPropertyOfTypeParams are parameters for getPropertyOfType (a named property of a type). */
+export interface GetPropertyOfTypeParams {
+    snapshot: number;
+    project: string;
+    type: number;
+    name: string;
+}
+
+/** IndexInfoResponse represents a single index signature. */
+export interface IndexInfoResponse {
+    keyType: TypeResponse;
+    valueType: TypeResponse;
+    isReadonly?: boolean;
+    declaration?: string;
+}
+
+export interface GetImportAdderEditsParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    actions: readonly ImportAdderAction[] | null;
+}
+
+export interface TextEdit {
+    pos: number;
+    end: number;
+    newText: string;
+}
+
+/** CheckerNodeParams are parameters for checker methods that operate on a node location. */
+export interface CheckerNodeParams {
+    snapshot: number;
+    project: string;
+    location: string;
+}
+
+/** CheckerSymbolParams are parameters for checker methods that operate on a symbol. */
+export interface CheckerSymbolParams {
+    snapshot: number;
+    project: string;
+    symbol: number;
+}
+
+/** GetMemberInModuleExportsParams are parameters for getMemberInModuleExports. */
+export interface GetMemberInModuleExportsParams {
+    snapshot: number;
+    project: string;
+    symbol: number;
+    name: string;
+}
+
+/**
+ * JSDocTagInfo is a single JSDoc tag, mirroring Strada's JSDocTagInfo but with the tag text
+ * rendered as a plain string rather than SymbolDisplayPart[].
+ */
+export interface JSDocTagInfo {
+    name: string;
+    text?: string;
+}
+
+/** GetReferencesToSymbolInFileParams are the parameters for the getReferencesToSymbolInFile method. */
+export interface GetReferencesToSymbolInFileParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    symbol: number;
+}
+
+/** GetReferencedSymbolsForNodeParams are the parameters for the getReferencedSymbolsForNode method. */
+export interface GetReferencedSymbolsForNodeParams {
+    snapshot: number;
+    project: string;
+    node: string;
+    position: number;
+}
+
+/** ReferencedSymbolEntry represents a symbol definition and its references. */
+export interface ReferencedSymbolEntry {
+    definition: string;
+    symbol?: SymbolResponse;
+    references: string[];
+}
+
+/** GetSignatureUsagesParams are the parameters for the getSignatureUsages method. */
+export interface GetSignatureUsagesParams {
+    snapshot: number;
+    project: string;
+    signatureDecl: string;
+}
+
+/** SignatureUsageResponse represents a single usage of a signature as a name-call pair. */
+export interface SignatureUsageResponse {
+    name: string;
+    call?: string;
+}
+
+/** GetCompletionsAtPositionParams are the parameters for the getCompletionsAtPosition method. */
+export interface GetCompletionsAtPositionParams {
+    snapshot: number;
+    project: string;
+    file: DocumentIdentifier;
+    position: number;
+    triggerCharacter?: string;
+    includeSymbol?: boolean;
+}
+
+/** CompletionInfoResponse wraps a list of completion entries. */
+export interface CompletionInfoResponse {
+    isIncomplete: boolean;
+    entries: CompletionEntryResponse[];
+}
+
+/** GetDiagnosticsParams are parameters for per-file diagnostic methods. */
+export interface GetDiagnosticsParams {
+    snapshot: number;
+    project: string;
+    files?: readonly DocumentIdentifier[];
+}
+
+/** DiagnosticResponse is the API response for a single diagnostic. */
+export interface DiagnosticResponse {
+    /** FileName is the path of the file this diagnostic belongs to, if any. */
+    fileName?: string;
+    /** Pos is the start position of the diagnostic in the source file. */
+    pos: number;
+    /** End is the end position of the diagnostic in the source file. */
+    end: number;
+    /** Code is the diagnostic error code. */
+    code: number;
+    /** Category is the diagnostic category (error, warning, suggestion, message). */
+    category: number;
+    /** Text is the localized diagnostic message text. */
+    text: string;
+    /** ReportsUnnecessary indicates this diagnostic highlights unnecessary code. */
+    reportsUnnecessary?: boolean;
+    /** ReportsDeprecated indicates this diagnostic highlights deprecated code. */
+    reportsDeprecated?: boolean;
+    /** MessageChain contains chained diagnostic messages, if any. */
+    messageChain?: DiagnosticResponse[];
+    /** RelatedInformation contains related diagnostic information, if any. */
+    relatedInformation?: DiagnosticResponse[];
+}
+
+/** PrintNodeParams are the parameters for the printNode method. */
+export interface PrintNodeParams {
+    /** base64-encoded binary AST data */
+    data: string;
+    preserveSourceNewlines?: boolean;
+    neverAsciiEscape?: boolean;
+    terminateUnterminatedLiterals?: boolean;
+}
+
+/** FormatNodeForInsertionParams are the parameters for the formatNodeForInsertion method. */
+export interface FormatNodeForInsertionParams {
+    snapshot: number;
+    project: string;
+    /** target file where the node will be inserted */
+    file: DocumentIdentifier;
+    /** UTF-16 code-unit offset of the insertion position in the target file */
+    position: number;
+    /** base64-encoded binary AST data for the synthesized node */
+    data: string;
+}
+
+export interface EmitParams {
+    snapshot: number;
+    project: string;
+    emitOnly?: number;
+}
+
+export interface EmitResponse {
+    emitSkipped: boolean;
+    diagnostics: DiagnosticResponse[];
+    emittedFiles: string[];
+}
+
+export interface EmitOutputResponse {
+    emitSkipped: boolean;
+    diagnostics: DiagnosticResponse[];
+    outputFiles: EmitOutputFile[];
+}
+
+export interface SelectedFilesEmitParams {
+    snapshot: number;
+    project: string;
+    files: readonly DocumentIdentifier[] | null;
+}
+
+/** GetIntrinsicTypeParams is used for intrinsic type getters (anyType, stringType, etc.). */
+export interface GetIntrinsicTypeParams {
+    snapshot: number;
+    project: string;
+}
+
+/**
+ * WellKnownSymbolsResponse carries the handle ids of the per-checker singleton
+ * symbols (unknown, undefined, arguments) so the client can identify them by id
+ * without a round-trip on every check.
+ */
+export interface WellKnownSymbolsResponse {
+    unknown: number;
+    undefined: number;
+    arguments: number;
+}
+
+/**
+ * WellKnownSignaturesResponse carries the handle id of the per-checker singleton
+ * unknown signature (the signature the checker yields when a call cannot be
+ * resolved) so the client can identify it by id without a round-trip on every check.
+ */
+export interface WellKnownSignaturesResponse {
+    unknown: number;
+}
+
+export interface ProfileParams {
+    dir: string;
+}
+
+export interface ProfileResult {
+    file: string;
+}
+
+/**
+ * APIFileChanges describes file changes to apply when updating a snapshot.
+ * Either InvalidateAll is true (discard all caches) or Changed/Created/Deleted
+ * list individual documents.
+ */
+export interface APIFileChanges {
+    invalidateAll?: boolean;
+    changed?: DocumentIdentifier[];
+    created?: DocumentIdentifier[];
+    deleted?: DocumentIdentifier[];
+}
+
+/**
+ * SnapshotChanges describes what changed between the previous latest snapshot
+ * and the newly created snapshot. Changes are reported per-project so clients
+ * can track cache refs at the (snapshot, project) level.
+ */
+export interface SnapshotChanges {
+    /**
+     * ChangedProjects maps project handles to the file changes within that project.
+     * Projects not listed here (and not in RemovedProjects) are unchanged.
+     */
+    changedProjects?: Record<string, ProjectFileChanges | null>;
+    /**
+     * RemovedProjects lists project handles that were present in the previous
+     * snapshot but absent from the new one.
+     */
+    removedProjects?: string[];
+}
+
+/** CompilerOptions contains the compiler options exposed by the API. */
+export interface CompilerOptions {
+    allowJs?: boolean;
+    allowArbitraryExtensions?: boolean;
+    allowImportingTsExtensions?: boolean;
+    allowNonTsExtensions?: boolean;
+    allowUmdGlobalAccess?: boolean;
+    allowUnreachableCode?: boolean;
+    allowUnusedLabels?: boolean;
+    assumeChangesOnlyAffectDirectDependencies?: boolean;
+    checkJs?: boolean;
+    customConditions?: string[];
+    composite?: boolean;
+    emitDeclarationOnly?: boolean;
+    emitBOM?: boolean;
+    emitDecoratorMetadata?: boolean;
+    declaration?: boolean;
+    declarationDir?: string;
+    declarationMap?: boolean;
+    deduplicatePackages?: boolean;
+    disableSizeLimit?: boolean;
+    disableSourceOfProjectReferenceRedirect?: boolean;
+    disableSolutionSearching?: boolean;
+    disableReferencedProjectLoad?: boolean;
+    erasableSyntaxOnly?: boolean;
+    exactOptionalPropertyTypes?: boolean;
+    experimentalDecorators?: boolean;
+    forceConsistentCasingInFileNames?: boolean;
+    isolatedModules?: boolean;
+    isolatedDeclarations?: boolean;
+    ignoreConfig?: boolean;
+    ignoreDeprecations?: string;
+    importHelpers?: boolean;
+    inlineSourceMap?: boolean;
+    inlineSources?: boolean;
+    init?: boolean;
+    incremental?: boolean;
+    jsx?: JsxEmit;
+    jsxFactory?: string;
+    jsxFragmentFactory?: string;
+    jsxImportSource?: string;
+    lib?: string[];
+    libReplacement?: boolean;
+    locale?: string;
+    mapRoot?: string;
+    module?: ModuleKind;
+    moduleResolution?: ModuleResolutionKind;
+    moduleSuffixes?: string[];
+    moduleDetection?: ModuleDetectionKind;
+    newLine?: NewLineKind;
+    noEmit?: boolean;
+    noCheck?: boolean;
+    noErrorTruncation?: boolean;
+    noFallthroughCasesInSwitch?: boolean;
+    noImplicitAny?: boolean;
+    noImplicitThis?: boolean;
+    noImplicitReturns?: boolean;
+    noEmitHelpers?: boolean;
+    noLib?: boolean;
+    noPropertyAccessFromIndexSignature?: boolean;
+    noUncheckedIndexedAccess?: boolean;
+    noEmitOnError?: boolean;
+    noUnusedLocals?: boolean;
+    noUnusedParameters?: boolean;
+    noResolve?: boolean;
+    noImplicitOverride?: boolean;
+    noUncheckedSideEffectImports?: boolean;
+    outDir?: string;
+    paths?: Record<string, string[]>;
+    preserveConstEnums?: boolean;
+    preserveSymlinks?: boolean;
+    project?: string;
+    resolveJsonModule?: boolean;
+    resolvePackageJsonExports?: boolean;
+    resolvePackageJsonImports?: boolean;
+    removeComments?: boolean;
+    rewriteRelativeImportExtensions?: boolean;
+    reactNamespace?: string;
+    rootDir?: string;
+    rootDirs?: string[];
+    skipLibCheck?: boolean;
+    stableTypeOrdering?: boolean;
+    strict?: boolean;
+    strictBindCallApply?: boolean;
+    strictBuiltinIteratorReturn?: boolean;
+    strictFunctionTypes?: boolean;
+    strictNullChecks?: boolean;
+    strictPropertyInitialization?: boolean;
+    stripInternal?: boolean;
+    skipDefaultLibCheck?: boolean;
+    sourceMap?: boolean;
+    sourceRoot?: string;
+    suppressOutputPathCheck?: boolean;
+    target?: ScriptTarget;
+    traceResolution?: boolean;
+    tsBuildInfoFile?: string;
+    typeRoots?: string[];
+    types?: string[];
+    useDefineForClassFields?: boolean;
+    useUnknownInCatchVariables?: boolean;
+    verbatimModuleSyntax?: boolean;
+    maxNodeModuleJsDepth?: number;
+    /** Internal fields */
+    configFilePath?: string;
+}
+
+export interface ProjectReference {
+    /** Path is a normalized path on disk. */
+    path: string;
+    /** OriginalPath is the path as it was originally written. */
+    originalPath: string;
+    /** Circular indicates that this reference is intended to form a circularity. */
+    circular: boolean;
+}
+
+export interface TypeAcquisition {
+    enable?: boolean;
+    include?: string[];
+    exclude?: string[];
+    disableFilenameBasedTypeAcquisition?: boolean;
+}
+
+export interface TranspileOptions {
+    compilerOptions?: CompilerOptions;
+    fileName?: string;
+    reportDiagnostics?: boolean;
+}
+
+export interface ImportAdderAction {
+    kind: "importSymbol";
+    symbol?: number;
+    isValidTypeOnlyUseSite?: boolean;
+}
+
+/** CompletionEntryResponse represents a single completion item. */
+export interface CompletionEntryResponse {
+    name: string;
+    kind?: number;
+    sortText?: string;
+    insertText?: string;
+    filterText?: string;
+    detail?: string;
+    labelDetails?: CompletionEntryLabelDetailsResponse;
+    symbol?: SymbolResponse;
+}
+
+export interface EmitOutputFile {
+    fileName: string;
+    text: string;
+    sourceFileName?: string;
+}
+
+/** ProjectFileChanges describes what source files changed within a single project. */
+export interface ProjectFileChanges {
+    /** ChangedFiles lists source file paths whose content differs. */
+    changedFiles?: string[];
+    /** DeletedFiles lists source file paths removed from the project's program. */
+    deletedFiles?: string[];
+}
+
+/** CompletionEntryLabelDetailsResponse holds additional label display text for a completion entry. */
+export interface CompletionEntryLabelDetailsResponse {
+    detail?: string;
+    description?: string;
+}
diff --git a/_packages/native-preview/src/api/proto.ts b/_packages/native-preview/src/api/proto.ts
index 1624f0e14d9..4f9b56b55b6 100644
--- a/_packages/native-preview/src/api/proto.ts
+++ b/_packages/native-preview/src/api/proto.ts
@@ -1,30 +1,29 @@
-import type { CheckFlags } from "#enums/checkFlags";
-import type { CompletionItemKind } from "#enums/completionItemKind";
-import type { DiagnosticCategory } from "#enums/diagnosticCategory";
-import type { ModuleKind } from "#enums/moduleKind";
-import type {
-    __String,
-    Path,
-} from "../ast/index.ts";
-import type { CompilerOptions } from "./compilerOptions.ts";
 import {
     documentURIToFileName,
     fileNameToDocumentURI,
 } from "./path.ts";
-
-export type { CompilerOptions } from "./compilerOptions.ts";
-
-/**
- * A document identifier that can be either a file name (path string) or a document URI object.
- *
- * @example
- * // Using a file name
- * project.program.getSourceFile("/path/to/file.ts");
- *
- * // Using a URI
- * project.program.getSourceFile({ uri: "file:///path/to/file.ts" });
- */
-export type DocumentIdentifier = string | { uri: string; };
+import type {
+    APIMethodInfo,
+    DocumentIdentifier,
+    SignatureResponse,
+    SourceFileResponse,
+    SymbolResponse,
+    TypeResponse,
+    UpdateSnapshotParams as CoreUpdateSnapshotParams,
+} from "./proto.generated.ts";
+export type { ConfigFileResponse as ParsedCommandLine, DiagnosticResponse as Diagnostic } from "./proto.generated.ts";
+
+export * from "./proto.generated.ts";
+
+export type APIMethodsReturning<T> = { [K in keyof APIMethodInfo]: [T] extends [NonNullable<APIMethodInfo[K]["result"]>] ? [NonNullable<APIMethodInfo[K]["result"]>] extends [T] ? K : never : never; }[keyof APIMethodInfo];
+
+export type SourceFileResponseMethod = APIMethodsReturning<SourceFileResponse>;
+export type SymbolPropertyMethod = APIMethodsReturning<SymbolResponse>;
+export type SymbolsPropertyMethod = APIMethodsReturning<SymbolResponse[]>;
+export type SignaturePropertyMethod = APIMethodsReturning<SignatureResponse>;
+export type TypePropertyMethod = Exclude<APIMethodsReturning<TypeResponse>, IntrinsicTypeMethod>;
+export type TypesPropertyMethod = APIMethodsReturning<TypeResponse[]>;
+export type IntrinsicTypeMethod = "getAnyType" | "getBigIntType" | "getBooleanType" | "getESSymbolType" | "getNeverType" | "getNonPrimitiveType" | "getNullType" | "getNumberType" | "getStringType" | "getUndefinedType" | "getUnknownType" | "getVoidType";
 
 /**
  * A position within a document, combining a document identifier with an offset.
@@ -36,20 +35,6 @@ export interface DocumentPosition {
     position: number;
 }
 
-export interface TextEdit {
-    pos: number;
-    end: number;
-    newText: string;
-}
-
-export interface ImportSymbolActionRequest {
-    kind: "importSymbol";
-    symbol: number;
-    isValidTypeOnlyUseSite?: boolean;
-}
-
-export type ImportAdderActionRequest = ImportSymbolActionRequest;
-
 /**
  * Resolves a DocumentIdentifier to a file name.
  * If the identifier contains a URI, it is converted to a file name.
@@ -72,135 +57,26 @@ export function resolveDocumentURI(identifier: DocumentIdentifier): string {
     return identifier.uri;
 }
 
-/**
- * Response from the initialize method.
- */
-export interface InitializeResponse {
-    /** Whether the host file system is case-sensitive */
-    useCaseSensitiveFileNames: boolean;
-    /** The server's current working directory */
-    currentDirectory: string;
-}
-
-export interface TypeAcquisition {
-    enable?: boolean;
-    include?: string[];
-    exclude?: string[];
-    disableFilenameBasedTypeAcquisition?: boolean;
-}
-
-export interface ProjectReference {
-    /** A normalized path on disk */
-    path: string;
-    /** The path as the user originally wrote it */
-    originalPath?: string;
-    /** True if it is intended that this reference form a circularity */
-    circular?: boolean;
-}
-
-/**
- * A diagnostic message from the TypeScript compiler.
- */
-export interface Diagnostic {
-    /** File name of the source file this diagnostic belongs to, if any */
-    readonly fileName?: string | undefined;
-    /** Start position of the diagnostic */
-    readonly pos: number;
-    /** End position of the diagnostic */
-    readonly end: number;
-    /** Diagnostic error code */
-    readonly code: number;
-    /** Diagnostic category (error, warning, suggestion, message) */
-    readonly category: DiagnosticCategory;
-    /** Localized diagnostic message text */
-    readonly text: string;
-    /** Whether this diagnostic highlights unnecessary code */
-    readonly reportsUnnecessary?: boolean | undefined;
-    /** Whether this diagnostic highlights deprecated code */
-    readonly reportsDeprecated?: boolean | undefined;
-    /** Chained diagnostic messages */
-    readonly messageChain?: readonly Diagnostic[] | undefined;
-    /** Related diagnostic information */
-    readonly relatedInformation?: readonly Diagnostic[] | undefined;
-}
-
-export interface ParsedCommandLine {
-    options: CompilerOptions;
-    fileNames: string[];
-    projectReferences?: ProjectReference[];
-    typeAcquisition?: TypeAcquisition;
-    compileOnSave?: boolean;
-    raw?: any;
-    errors: readonly Diagnostic[];
-}
-
-export interface ReadConfigFileResult {
-    config: any;
-    error?: Diagnostic;
-}
-
-export interface LSPUpdateSnapshotParams {
+export interface LSPUpdateSnapshotParams extends CoreUpdateSnapshotParams {
     /**
      * @deprecated Use {@link openProjects} instead.
      * Path to a tsconfig.json file to open in the new snapshot.
      */
     openProject?: string;
-    /**
-     * tsconfig.json files to open/load in the new snapshot. Opens are ref-counted
-     * and persist across snapshots until closed via {@link closeProjects}.
-     */
-    openProjects?: DocumentIdentifier[];
-    /**
-     * tsconfig.json files to release in the new snapshot. A project is only unloaded
-     * once every API client that opened it closes it.
-     */
-    closeProjects?: DocumentIdentifier[];
-    /**
-     * Files to keep open for the API client, mirroring LSP's `textDocument/didOpen`.
-     * For each file, ancestor directories are searched for a tsconfig that contains it;
-     * if one is found, that configured project is loaded and becomes the file's default
-     * project. Otherwise the file is loaded into the inferred project (e.g. a d.ts in
-     * node_modules that is not part of any project's import graph). Opens persist across
-     * subsequent snapshots until the file is closed via {@link closeFiles}.
-     * After calling updateSnapshot with openFiles, getDefaultProjectForFile returns the
-     * resolved configured or inferred project.
-     */
-    openFiles?: DocumentIdentifier[];
-    /**
-     * Files to release in the new snapshot. A file is only fully closed once every
-     * API client that opened it closes it.
-     */
-    closeFiles?: DocumentIdentifier[];
-}
-
-export interface FileChangeSummary {
-    changed?: DocumentIdentifier[];
-    created?: DocumentIdentifier[];
-    deleted?: DocumentIdentifier[];
-}
 
-export type FileChanges = FileChangeSummary | { invalidateAll: true; };
-
-/**
- * Parameters for updateSnapshot.
- */
-export interface UpdateSnapshotParams extends LSPUpdateSnapshotParams {
-    fileChanges?: FileChanges;
+    /** FileChanges are not supplied by the LSP */
+    fileChanges?: never;
 }
 
 /**
- * Parameters for updateTemporarySnapshot. Unlike {@link UpdateSnapshotParams}, this
- * only overrides a single file's content: it does not open or close projects/files
- * and does not advance the session's latest snapshot. The resulting snapshot is only
- * for the caller's own queries and must be released when done.
+ * Parameters for updateSnapshot, including deprecated members handled by `toUpdateSnapshotRequest`
  */
-export interface UpdateTemporarySnapshotParams {
-    /** The current client snapshot on which to layer the temporary update. */
-    snapshot: number;
-    /** The file whose content is temporarily overridden. */
-    file: DocumentIdentifier;
-    /** The temporary content for the file. */
-    newText: string;
+export interface UpdateSnapshotParams extends CoreUpdateSnapshotParams {
+    /**
+     * @deprecated Use {@link openProjects} instead.
+     * Path to a tsconfig.json file to open in the new snapshot.
+     */
+    openProject?: string;
 }
 
 /**
@@ -218,157 +94,3 @@ export function toUpdateSnapshotRequest(params?: UpdateSnapshotParams): UpdateSn
         ...(mergedOpenProjects !== undefined ? { openProjects: mergedOpenProjects } : {}),
     };
 }
-
-/**
- * Changes to source files within a single project.
- */
-export interface ProjectFileChanges {
-    /** Source file paths whose content changed */
-    changedFiles?: string[];
-    /** Source file paths removed from the project's program */
-    deletedFiles?: string[];
-}
-
-/**
- * Changes between two consecutive snapshots, reported per-project.
- */
-export interface SnapshotChanges {
-    /** Project handles mapped to their file changes. Projects not listed are unchanged. */
-    changedProjects?: Record<string, ProjectFileChanges>;
-    /** Project handles that were removed from the snapshot */
-    removedProjects?: string[];
-}
-
-/**
- * Response from updateSnapshot.
- */
-export interface UpdateSnapshotResponse {
-    /** Handle for the newly created snapshot */
-    snapshot: number;
-    /** List of projects in the snapshot */
-    projects: ProjectResponse[];
-    /** Changes from the previous snapshot (absent for the first snapshot) */
-    changes?: SnapshotChanges;
-}
-
-export interface ProjectResponse {
-    id: Path;
-    configFileName: string;
-    parsedCommandLine: ParsedCommandLine;
-    /** @deprecated Use `parsedCommandLine.options`. */
-    compilerOptions: CompilerOptions;
-    /** @deprecated Use `parsedCommandLine.fileNames`. */
-    rootFiles: string[];
-}
-
-export interface SourceFileResponse {
-    /** Base64-encoded binary AST data */
-    data: string;
-}
-
-export interface SourceFileMetadata {
-    isDefaultLibrary: boolean;
-    isFromExternalLibrary: boolean;
-    packageJsonType: string;
-    packageJsonDirectory: string;
-    impliedNodeFormat: ModuleKind;
-}
-
-export interface SymbolResponse {
-    id: number;
-    /**
-     * The project the symbol was first observed in. Used as the default project for
-     * follow-up lookups that need a project context (e.g. members/exports), since symbols
-     * are shared snapshot-wide and such lookups can vary by project.
-     */
-    project: Path;
-    name: __String;
-    flags: number;
-    checkFlags: CheckFlags;
-    declarations?: string[];
-    valueDeclaration?: string;
-    parent?: number;
-    exportSymbol?: number;
-}
-
-export interface TypeResponse {
-    id: number;
-    flags: number;
-    objectFlags?: number;
-    /** Literal value. BigInt literals are encoded as a decimal string (e.g. "-123") since JSON cannot represent bigint. Absent values are serialized as null. */
-    value?: string | number | boolean | null;
-    freshType?: number;
-    regularType?: number;
-    target?: number;
-    typeParameters?: number[];
-    outerTypeParameters?: number[];
-    localTypeParameters?: number[];
-    elementFlags?: number[];
-    fixedLength?: number;
-    readonly?: boolean;
-    objectType?: number;
-    indexType?: number;
-    checkType?: number;
-    extendsType?: number;
-    baseType?: number;
-    substConstraint?: number;
-    texts?: string[];
-    intrinsicName?: string;
-    isThisType?: boolean;
-    aliasTypeArguments?: number[];
-    aliasSymbol?: number;
-    symbol?: number;
-}
-
-export interface SignatureResponse {
-    id: number;
-    flags: number;
-    declaration?: string;
-    typeParameters?: number[];
-    parameters?: number[];
-    thisParameter?: number;
-    target?: number;
-}
-
-export interface TypePredicateResponse {
-    kind: number;
-    parameterIndex: number;
-    parameterName?: string;
-    type?: TypeResponse;
-}
-
-export interface IndexInfoResponse {
-    keyType: TypeResponse;
-    valueType: TypeResponse;
-    isReadonly?: boolean;
-    declaration?: string;
-}
-
-export interface ProfileParams {
-    dir: string;
-}
-
-export interface ProfileResult {
-    file: string;
-}
-
-export interface CompletionEntryLabelDetailsResponse {
-    detail?: string;
-    description?: string;
-}
-
-export interface CompletionEntryResponse {
-    name: string;
-    kind?: CompletionItemKind;
-    sortText?: string;
-    insertText?: string;
-    filterText?: string;
-    detail?: string;
-    labelDetails?: CompletionEntryLabelDetailsResponse;
-    symbol?: SymbolResponse;
-}
-
-export interface CompletionInfoResponse {
-    isIncomplete: boolean;
-    entries: CompletionEntryResponse[];
-}
diff --git a/_packages/native-preview/src/api/sync/api.ts b/_packages/native-preview/src/api/sync/api.ts
index caaec748b1d..253ed1d1f93 100644
--- a/_packages/native-preview/src/api/sync/api.ts
+++ b/_packages/native-preview/src/api/sync/api.ts
@@ -57,26 +57,28 @@ import {
 } from "../path.ts";
 import type {
     CompilerOptions,
-    CompletionInfoResponse,
+    Diagnostic,
     DocumentIdentifier,
     DocumentPosition,
-    ImportAdderActionRequest,
-    ImportSymbolActionRequest,
-    IndexInfoResponse,
-    InitializeResponse,
+    EmitOutputResponse as ProtocolEmitOutputResponse,
+    ImportAdderAction,
+    IntrinsicTypeMethod,
     LSPUpdateSnapshotParams,
     ParsedCommandLine,
-    ProfileResult,
     ProjectReference,
     ProjectResponse,
-    ReadConfigFileResult,
+    ReadConfigFileResponse,
+    SignaturePropertyMethod,
     SignatureResponse,
     SourceFileMetadata,
+    SymbolPropertyMethod,
     SymbolResponse,
+    SymbolsPropertyMethod,
     TextEdit,
     TypeAcquisition,
-    TypePredicateResponse,
+    TypePropertyMethod,
     TypeResponse,
+    TypesPropertyMethod,
     UpdateSnapshotParams,
     UpdateSnapshotResponse,
 } from "../proto.ts";
@@ -104,14 +106,13 @@ import type {
     CompletionInfo,
     CompletionOptions,
     ConditionalType,
-    Diagnostic,
     EmitOutput,
     EmitOutputFile,
     EmitResult,
     FreshableType,
     GetImportEditsForSymbolsOptions,
     IdentifierTypePredicate,
-    ImportAdderAction,
+    ImportAdderAction as APIImportAdderAction,
     IndexedAccessType,
     IndexInfo,
     IndexType,
@@ -140,13 +141,64 @@ import type {
 
 export { documentURIToFileName, fileNameToDocumentURI } from "../path.ts";
 export { CheckFlags, CompletionItemKind, DiagnosticCategory, ElementFlags, EmitOnly, ModifierFlags, ModuleKind, NodeBuilderFlags, ObjectFlags, SignatureFlags, SignatureKind, SymbolFlags, TypeFlags, TypePredicateKind };
-export type { APIOptions, AssertsIdentifierTypePredicate, AssertsThisTypePredicate, BigIntLiteralType, BooleanLiteralType, ClientSocketOptions, ClientSpawnOptions, CompilerOptions, CompletionEntry, CompletionInfo, CompletionOptions, ConditionalType, Diagnostic, DocumentIdentifier, DocumentPosition, EmitOutput, EmitOutputFile, EmitResult, FreshableType, GetImportEditsForSymbolsOptions, IdentifierTypePredicate, ImportAdderAction, IndexedAccessType, IndexInfo, IndexType, InterfaceType, IntersectionType, IntrinsicType, JSDocTagInfo, LiteralType, LSPConnectionOptions, NumberLiteralType, ObjectType, ParsedCommandLine, ProjectReference, ReadConfigFileResult, RequestTiming, SourceFileMetadata, StringLiteralType, StringMappingType, StructuredType, SubstitutionType, TemplateLiteralType, TextEdit, ThisTypePredicate, TimingAccumulators, TimingInfo, TupleType, Type, TypeAcquisition, TypeParameter, TypePredicate, TypePredicateBase, TypeReference, UnionOrIntersectionType, UnionType };
-
-interface EmitOutputResponse {
-    readonly emitSkipped: boolean;
-    readonly diagnostics: readonly Diagnostic[];
-    readonly outputFiles: readonly (EmitOutputFile & { readonly fileName: string; })[];
-}
+export type {
+    APIImportAdderAction as ImportAdderAction,
+    APIOptions,
+    AssertsIdentifierTypePredicate,
+    AssertsThisTypePredicate,
+    BigIntLiteralType,
+    BooleanLiteralType,
+    ClientSocketOptions,
+    ClientSpawnOptions,
+    CompilerOptions,
+    CompletionEntry,
+    CompletionInfo,
+    CompletionOptions,
+    ConditionalType,
+    Diagnostic,
+    DocumentIdentifier,
+    DocumentPosition,
+    EmitOutput,
+    EmitOutputFile,
+    EmitResult,
+    FreshableType,
+    GetImportEditsForSymbolsOptions,
+    IdentifierTypePredicate,
+    IndexedAccessType,
+    IndexInfo,
+    IndexType,
+    InterfaceType,
+    IntersectionType,
+    IntrinsicType,
+    JSDocTagInfo,
+    LiteralType,
+    LSPConnectionOptions,
+    NumberLiteralType,
+    ObjectType,
+    ParsedCommandLine,
+    ProjectReference,
+    ReadConfigFileResponse,
+    RequestTiming,
+    SourceFileMetadata,
+    StringLiteralType,
+    StringMappingType,
+    StructuredType,
+    SubstitutionType,
+    TemplateLiteralType,
+    TextEdit,
+    ThisTypePredicate,
+    TimingAccumulators,
+    TimingInfo,
+    TupleType,
+    Type,
+    TypeAcquisition,
+    TypeParameter,
+    TypePredicate,
+    TypePredicateBase,
+    TypeReference,
+    UnionOrIntersectionType,
+    UnionType,
+};
 
 export interface TranspileOptions {
     compilerOptions?: CompilerOptions;
@@ -180,14 +232,14 @@ export class API<FromLSP extends boolean = false> {
      * Use this when connecting to an API pipe provided by an LSP server via custom/initializeAPISession.
      */
     static fromLSPConnection(options: LSPConnectionOptions): API<true> {
-        const api = new API(options);
+        const api = new API<true>(options);
         api.ensureInitialized();
         return api;
     }
 
     private ensureInitialized(): void {
         if (!this.initialized) {
-            const response = this.client.apiRequest<InitializeResponse>("initialize", null);
+            const response = this.client.apiRequest("initialize", null);
             const getCanonicalFileName = createGetCanonicalFileName(response.useCaseSensitiveFileNames);
             const currentDirectory = response.currentDirectory;
             this.toPath = (fileName: string) => toPath(fileName, currentDirectory, getCanonicalFileName) as Path;
@@ -197,17 +249,17 @@ export class API<FromLSP extends boolean = false> {
 
     parseConfigFile(file: DocumentIdentifier): ParsedCommandLine {
         this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseConfigFile", { file });
+        return this.client.apiRequest("parseConfigFile", { file });
     }
 
     parseCommandLine(commandLine: readonly string[]): ParsedCommandLine {
         this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseCommandLine", { commandLine });
+        return this.client.apiRequest("parseCommandLine", { commandLine });
     }
 
-    readConfigFile(file: DocumentIdentifier): ReadConfigFileResult {
+    readConfigFile(file: DocumentIdentifier): ReadConfigFileResponse {
         this.ensureInitialized();
-        return this.client.apiRequest<ReadConfigFileResult>("readConfigFile", { file });
+        return this.client.apiRequest("readConfigFile", { file });
     }
 
     parseJsonConfigFileContent(
@@ -217,34 +269,34 @@ export class API<FromLSP extends boolean = false> {
             | { configFileName: DocumentIdentifier; configDirectory?: never; },
     ): ParsedCommandLine {
         this.ensureInitialized();
-        return this.client.apiRequest<ParsedCommandLine>("parseJsonConfigFileContent", { json, ...options });
+        return this.client.apiRequest("parseJsonConfigFileContent", { json, ...options });
     }
 
     transpileModule(input: string, options: TranspileOptions = {}): TranspileOutput {
         this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileModule", { input, options });
+        return this.client.apiRequest("transpileModule", { input, options });
     }
 
     transpileModuleFromFile(fileName: string, options: TranspileOptions = {}): TranspileOutput {
         this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileModuleFromFile", { fileName, options });
+        return this.client.apiRequest("transpileModuleFromFile", { fileName, options });
     }
 
     transpileDeclaration(input: string, options: TranspileOptions = {}): TranspileOutput {
         this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileDeclaration", { input, options });
+        return this.client.apiRequest("transpileDeclaration", { input, options });
     }
 
     transpileDeclarationFromFile(fileName: string, options: TranspileOptions = {}): TranspileOutput {
         this.ensureInitialized();
-        return this.client.apiRequest<TranspileOutput>("transpileDeclarationFromFile", { fileName, options });
+        return this.client.apiRequest("transpileDeclarationFromFile", { fileName, options });
     }
 
     updateSnapshot(params?: FromLSP extends true ? LSPUpdateSnapshotParams : UpdateSnapshotParams): Snapshot {
         this.ensureInitialized();
 
         const requestParams = toUpdateSnapshotRequest(params);
-        const data = this.client.apiRequest<UpdateSnapshotResponse>("updateSnapshot", requestParams);
+        const data = this.client.apiRequest("updateSnapshot", requestParams);
 
         // Retain cached source files from previous snapshot for unchanged files
         if (this.latestSnapshot) {
@@ -296,7 +348,7 @@ export class API<FromLSP extends boolean = false> {
         if (!this.activeSnapshots.has(baseSnapshot) || baseSnapshot.isDisposed()) {
             throw new Error("Cannot run a temporary file update on an inactive snapshot");
         }
-        const data = this.client.apiRequest<UpdateSnapshotResponse>("updateTemporarySnapshot", { snapshot: baseSnapshot.id, file, newText });
+        const data = this.client.apiRequest("updateTemporarySnapshot", { snapshot: baseSnapshot.id, file, newText });
 
         // Retain cached source files from the base snapshot for files unchanged by
         // the temporary update. The temporary snapshot is not the latest snapshot, so
@@ -361,13 +413,13 @@ export class InternalAPI {
 
     stopCPUProfile(): string {
         this.ensureInitialized();
-        const result = this.client.apiRequest<ProfileResult>("stopCPUProfile", null);
+        const result = this.client.apiRequest("stopCPUProfile", null);
         return result.file;
     }
 
     saveHeapProfile(dir: string): string {
         this.ensureInitialized();
-        const result = this.client.apiRequest<ProfileResult>("saveHeapProfile", { dir });
+        const result = this.client.apiRequest("saveHeapProfile", { dir });
         return result.file;
     }
 }
@@ -416,7 +468,7 @@ export class Snapshot {
 
     getDefaultProjectForFile(file: DocumentIdentifier): Project | undefined {
         this.ensureNotDisposed();
-        const data = this.client.apiRequest<ProjectResponse | null>("getDefaultProjectForFile", {
+        const data = this.client.apiRequest("getDefaultProjectForFile", {
             snapshot: this.id,
             file,
         });
@@ -485,12 +537,12 @@ class SnapshotObjectRegistry {
         this.symbols.clear();
     }
 
-    fetchSymbol(source: Symbol | Signature | Type, method: string, handle: number | undefined, projectId?: Path): Symbol {
+    fetchSymbol(source: Symbol | Signature | Type, method: SymbolPropertyMethod, handle: number | undefined, projectId: Path): Symbol {
         if (!handle) return undefined as unknown as Symbol;
         const cached = this.getSymbol(handle);
         if (cached) return cached;
 
-        const data = this.client.apiRequest<SymbolResponse | null>(method, {
+        const data = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: projectId,
             objectId: source.id,
@@ -499,7 +551,7 @@ class SnapshotObjectRegistry {
         return this.getOrCreateSymbol(data);
     }
 
-    fetchSymbols(source: Symbol | Signature | Type, method: string, handles?: readonly number[], projectId?: Path): readonly Symbol[] {
+    fetchSymbols(source: Symbol | Signature | Type, method: SymbolsPropertyMethod, handles: readonly number[] | undefined, projectId: Path): readonly Symbol[] {
         if (handles) {
             const result = new Array<Symbol>(handles.length);
             let allCached = true;
@@ -513,7 +565,7 @@ class SnapshotObjectRegistry {
             }
             if (allCached) return result;
         }
-        const symbolData = this.client.apiRequest<SymbolResponse[] | null>(method, {
+        const symbolData = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: projectId,
             objectId: source.id,
@@ -582,14 +634,14 @@ class ProjectObjectRegistry {
         this.signatures.clear();
     }
 
-    fetchOptionalType<T extends Type>(source: Symbol | Signature | Type, method: string, handle: number | false | undefined): T | undefined {
+    fetchOptionalType<T extends Type>(source: Symbol | Signature | Type, method: TypePropertyMethod, handle: number | false | undefined): T | undefined {
         if (handle !== false) {
             if (!handle) return undefined;
             const cached = this.getType(handle);
             if (cached) return cached as unknown as T;
         }
 
-        const data = this.client.apiRequest<TypeResponse | null>(method, {
+        const data = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -598,22 +650,22 @@ class ProjectObjectRegistry {
         return this.getOrCreateType(data) as unknown as T;
     }
 
-    fetchType<T extends Type>(source: Symbol | Signature | Type, method: string, handle: number | false | undefined): T {
+    fetchType<T extends Type>(source: Symbol | Signature | Type, method: TypePropertyMethod, handle: number | false | undefined): T {
         const result = this.fetchOptionalType<T>(source, method, handle);
         if (result === undefined) throw new Error(`${method} returned no type for ${source.constructor.name} ${source.id}`);
         return result;
     }
 
-    fetchSymbol(source: Symbol | Signature | Type, method: string, handle: number | undefined): Symbol {
+    fetchSymbol(source: Symbol | Signature | Type, method: SymbolPropertyMethod, handle: number | undefined): Symbol {
         return this.snapshotRegistry.fetchSymbol(source, method, handle, this.project.id);
     }
 
-    fetchSignature(source: Symbol | Signature | Type, method: string, handle: number | undefined): Signature {
+    fetchSignature(source: Symbol | Signature | Type, method: SignaturePropertyMethod, handle: number | undefined): Signature {
         if (!handle) return undefined as unknown as Signature;
         const cached = this.getSignature(handle);
         if (cached) return cached;
 
-        const data = this.client.apiRequest<SignatureResponse | null>(method, {
+        const data = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -622,7 +674,7 @@ class ProjectObjectRegistry {
         return this.getOrCreateSignature(data);
     }
 
-    fetchTypes(source: Symbol | Signature | Type, method: string, handles?: readonly number[]): readonly Type[] {
+    fetchTypes(source: Symbol | Signature | Type, method: TypesPropertyMethod, handles?: readonly number[]): readonly Type[] {
         if (handles) {
             const result = new Array<Type>(handles.length);
             let allCached = true;
@@ -636,7 +688,7 @@ class ProjectObjectRegistry {
             }
             if (allCached) return result;
         }
-        const typesData = this.client.apiRequest<TypeResponse[] | null>(method, {
+        const typesData = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -645,14 +697,14 @@ class ProjectObjectRegistry {
         else return typesData.map(data => this.getOrCreateType(data));
     }
 
-    fetchSymbols(source: Symbol | Signature | Type, method: string, handles?: readonly number[]): readonly Symbol[] {
+    fetchSymbols(source: Symbol | Signature | Type, method: SymbolsPropertyMethod, handles?: readonly number[]): readonly Symbol[] {
         return this.snapshotRegistry.fetchSymbols(source, method, handles, this.project.id);
     }
 
     // getBaseTypes is a checker-level endpoint keyed by `type` (not `objectId`),
     // so it cannot go through fetchTypes. This helper reuses that server method.
     fetchBaseTypes(source: Type): readonly Type[] {
-        const typesData = this.client.apiRequest<TypeResponse[] | null>("getBaseTypes", {
+        const typesData = this.client.apiRequest("getBaseTypes", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -662,7 +714,7 @@ class ProjectObjectRegistry {
     }
 
     fetchPropertiesOfType(source: Type): readonly Symbol[] {
-        const data = this.client.apiRequest<SymbolResponse[] | null>("getPropertiesOfType", {
+        const data = this.client.apiRequest("getPropertiesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -671,7 +723,7 @@ class ProjectObjectRegistry {
     }
 
     fetchApparentPropertiesOfType(source: Type): readonly Symbol[] {
-        const data = this.client.apiRequest<SymbolResponse[] | null>("getApparentPropertiesOfType", {
+        const data = this.client.apiRequest("getApparentPropertiesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             objectId: source.id,
@@ -680,7 +732,7 @@ class ProjectObjectRegistry {
     }
 
     fetchPropertyOfType(source: Type, name: string): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getPropertyOfType", {
+        const data = this.client.apiRequest("getPropertyOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -690,7 +742,7 @@ class ProjectObjectRegistry {
     }
 
     fetchSignaturesOfType(source: Type, kind: SignatureKind): readonly Signature[] {
-        const data = this.client.apiRequest<SignatureResponse[]>("getSignaturesOfType", {
+        const data = this.client.apiRequest("getSignaturesOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -700,7 +752,7 @@ class ProjectObjectRegistry {
     }
 
     fetchIndexInfosOfType(source: Type): readonly IndexInfo[] {
-        const data = this.client.apiRequest<IndexInfoResponse[] | null>("getIndexInfosOfType", {
+        const data = this.client.apiRequest("getIndexInfosOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: source.id,
@@ -715,7 +767,7 @@ class ProjectObjectRegistry {
     }
 
     fetchTypeParameterAtPosition(source: Signature, pos: number): Type {
-        const data = this.client.apiRequest<TypeResponse>("getTypeParameterAtPosition", {
+        const data = this.client.apiRequest("getTypeParameterAtPosition", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: source.id,
@@ -749,8 +801,11 @@ export class Project {
         toPath: (fileName: string) => Path,
         snapshotRegistry: SnapshotObjectRegistry,
     ) {
-        this.id = data.id;
+        this.id = data.id as Path;
         this.configFileName = data.configFileName;
+        if (!data.parsedCommandLine?.options) {
+            throw new Error(`Project '${data.configFileName}' has no parsed command line`);
+        }
         this.parsedCommandLine = data.parsedCommandLine;
         this.compilerOptions = this.parsedCommandLine.options;
         this.rootFiles = this.parsedCommandLine.fileNames;
@@ -775,7 +830,7 @@ export class Project {
     }
 
     /** @deprecated Use `languageService.getImportAdderEdits`. */
-    getImportAdderEdits(file: DocumentIdentifier, actions: readonly ImportAdderAction[]): readonly TextEdit[] {
+    getImportAdderEdits(file: DocumentIdentifier, actions: readonly APIImportAdderAction[]): readonly TextEdit[] {
         return this.languageService.getImportAdderEdits(file, actions);
     }
 
@@ -807,11 +862,11 @@ export class LanguageService {
         this.objectRegistry = objectRegistry;
     }
 
-    getImportAdderEdits(file: DocumentIdentifier, actions: readonly ImportAdderAction[]): readonly TextEdit[] {
-        const requestActions: ImportAdderActionRequest[] = actions.map(action => {
+    getImportAdderEdits(file: DocumentIdentifier, actions: readonly APIImportAdderAction[]): readonly TextEdit[] {
+        const requestActions: ImportAdderAction[] = actions.map(action => {
             switch (action.kind) {
                 case "importSymbol":
-                    const importSymbolAction: ImportSymbolActionRequest = {
+                    const importSymbolAction: ImportAdderAction = {
                         kind: "importSymbol",
                         symbol: action.symbol.id,
                     };
@@ -824,7 +879,7 @@ export class LanguageService {
             }
         });
 
-        const data = this.client.apiRequest<TextEdit[]>("getImportAdderEdits", {
+        const data = this.client.apiRequest("getImportAdderEdits", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -836,7 +891,7 @@ export class LanguageService {
     getImportEditsForSymbols(file: DocumentIdentifier, symbols: readonly Symbol[], options: GetImportEditsForSymbolsOptions = {}): readonly TextEdit[] {
         return this.getImportAdderEdits(
             file,
-            symbols.map((symbol): ImportAdderAction => {
+            symbols.map((symbol): APIImportAdderAction => {
                 if (options.isValidTypeOnlyUseSite !== undefined) {
                     return {
                         kind: "importSymbol",
@@ -853,7 +908,7 @@ export class LanguageService {
     }
 
     getReferencedSymbolsForNode(node: Node, position: number): ReferencedSymbolEntry[] {
-        const data = this.client.apiRequest<{ definition: string; symbol?: SymbolResponse; references: string[]; }[] | null>("getReferencedSymbolsForNode", {
+        const data = this.client.apiRequest("getReferencedSymbolsForNode", {
             snapshot: this.snapshotId,
             project: this.project.id,
             node: getNodeId(node),
@@ -867,7 +922,7 @@ export class LanguageService {
     }
 
     getSignatureUsage(signatureDecl: Node): SignatureUsage[] {
-        const data = this.client.apiRequest<{ name: string; call?: string; }[] | null>("getSignatureUsages", {
+        const data = this.client.apiRequest("getSignatureUsages", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signatureDecl: getNodeId(signatureDecl),
@@ -879,13 +934,13 @@ export class LanguageService {
     }
 
     getCompletionsAtPosition(document: string, position: number, options?: CompletionOptions): CompletionInfo | undefined {
-        const data = this.client.apiRequest<CompletionInfoResponse | null>("getCompletionsAtPosition", {
+        const data = this.client.apiRequest("getCompletionsAtPosition", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: document,
             position,
-            triggerCharacter: options?.triggerCharacter,
-            includeSymbol: options?.includeSymbol,
+            ...(options?.triggerCharacter !== undefined ? { triggerCharacter: options.triggerCharacter } : {}),
+            ...(options?.includeSymbol !== undefined ? { includeSymbol: options.includeSymbol } : {}),
         });
         if (!data) return undefined;
         return {
@@ -955,7 +1010,7 @@ export class Program {
     }
 
     getSourceFileNames(): readonly string[] {
-        const data = this.client.apiRequest<string[] | null>("getSourceFileNames", {
+        const data = this.client.apiRequest("getSourceFileNames", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -987,7 +1042,7 @@ export class Program {
     }
 
     private fetchSourceFileMetadata(path: Path): SourceFileMetadata | undefined {
-        const data = this.client.apiRequest<SourceFileMetadata | null>("getSourceFileMetadata", {
+        const data = this.client.apiRequest("getSourceFileMetadata", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: path,
@@ -1020,7 +1075,7 @@ export class Program {
      * Includes the root config file and any extended config files.
      */
     getConfigFileNames(): readonly string[] {
-        const data = this.client.apiRequest<string[]>("getConfigFileNames", {
+        const data = this.client.apiRequest("getConfigFileNames", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1045,8 +1100,6 @@ export class Program {
     }
 
     /**
-     * Get syntactic (parse) diagnostics for a specific file or all files.
-     * @param file - Optional file to get diagnostics for. If omitted, returns diagnostics for all files.
      * Get syntactic (parse) diagnostics for specific files or all files.
      * @param file - Optional file(s) to get diagnostics for. If omitted, returns diagnostics for all files.
      */
@@ -1054,10 +1107,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = this.client.apiRequest<Diagnostic[]>("getSyntacticDiagnostics", {
+        const data = this.client.apiRequest("getSyntacticDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1070,10 +1123,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = this.client.apiRequest<Diagnostic[]>("getBindDiagnostics", {
+        const data = this.client.apiRequest("getBindDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1086,10 +1139,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = this.client.apiRequest<Diagnostic[]>("getSemanticDiagnostics", {
+        const data = this.client.apiRequest("getSemanticDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1102,10 +1155,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = this.client.apiRequest<Diagnostic[]>("getSuggestionDiagnostics", {
+        const data = this.client.apiRequest("getSuggestionDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1118,10 +1171,10 @@ export class Program {
         const files = file === undefined ? undefined
             : Array.isArray(file) ? file
             : [file];
-        const data = this.client.apiRequest<Diagnostic[]>("getDeclarationDiagnostics", {
+        const data = this.client.apiRequest("getDeclarationDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            files,
+            ...(files !== undefined ? { files } : {}),
         });
         return data ?? [];
     }
@@ -1130,7 +1183,7 @@ export class Program {
      * Get program-wide diagnostics for the project, including compiler options diagnostics.
      */
     getProgramDiagnostics(): readonly Diagnostic[] {
-        const data = this.client.apiRequest<Diagnostic[]>("getProgramDiagnostics", {
+        const data = this.client.apiRequest("getProgramDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1141,7 +1194,7 @@ export class Program {
      * Get global (non-file-specific) semantic diagnostics for the project.
      */
     getGlobalDiagnostics(): readonly Diagnostic[] {
-        const data = this.client.apiRequest<Diagnostic[]>("getGlobalDiagnostics", {
+        const data = this.client.apiRequest("getGlobalDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1152,7 +1205,7 @@ export class Program {
      * Get config file parsing diagnostics for the project.
      */
     getConfigFileParsingDiagnostics(): readonly Diagnostic[] {
-        const data = this.client.apiRequest<Diagnostic[]>("getConfigFileParsingDiagnostics", {
+        const data = this.client.apiRequest("getConfigFileParsingDiagnostics", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1166,21 +1219,26 @@ export class Program {
      * is written there. Otherwise, the server writes directly to the host filesystem.
      */
     emit(emitOnly?: EmitOnly): EmitResult {
-        return this.client.apiRequest<EmitResult>("emit", {
+        const response = this.client.apiRequest("emit", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            emitOnly,
+            ...(emitOnly !== undefined ? { emitOnly } : {}),
         });
+        return {
+            emitSkipped: response.emitSkipped,
+            diagnostics: response.diagnostics,
+            emittedFiles: response.emittedFiles,
+        };
     }
 
     /**
      * Emits files and returns their contents without writing to the filesystem.
      */
     emitToString(emitOnly?: EmitOnly): EmitOutput {
-        const response = this.client.apiRequest<EmitOutputResponse>("emitToString", {
+        const response = this.client.apiRequest("emitToString", {
             snapshot: this.snapshotId,
             project: this.project.id,
-            emitOnly,
+            ...(emitOnly !== undefined ? { emitOnly } : {}),
         });
         return toEmitOutput(response);
     }
@@ -1189,7 +1247,7 @@ export class Program {
      * Gets JavaScript output for selected files regardless of project `noEmit`, `emitDeclarationOnly`, and `noEmitOnError` settings.
      */
     getJavaScriptEmit(files: readonly DocumentIdentifier[]): EmitOutput {
-        const response = this.client.apiRequest<EmitOutputResponse>("getJavaScriptEmit", {
+        const response = this.client.apiRequest("getJavaScriptEmit", {
             snapshot: this.snapshotId,
             project: this.project.id,
             files,
@@ -1201,7 +1259,7 @@ export class Program {
      * Gets declaration output for selected files regardless of project `noEmit`, `declaration`, `emitDeclarationOnly`, and `noEmitOnError` settings.
      */
     getDeclarationEmit(files: readonly DocumentIdentifier[]): EmitOutput {
-        const response = this.client.apiRequest<EmitOutputResponse>("getDeclarationEmit", {
+        const response = this.client.apiRequest("getDeclarationEmit", {
             snapshot: this.snapshotId,
             project: this.project.id,
             files,
@@ -1210,7 +1268,7 @@ export class Program {
     }
 }
 
-function toEmitOutput(response: EmitOutputResponse): EmitOutput {
+function toEmitOutput(response: ProtocolEmitOutputResponse): EmitOutput {
     const outputFiles = new Map<string, EmitOutputFile>();
     for (const { fileName, ...outputFile } of response.outputFiles) {
         outputFiles.set(fileName, outputFile);
@@ -1250,14 +1308,14 @@ export class Checker {
     getSymbolAtLocation(nodes: readonly Node[]): (Symbol | undefined)[];
     getSymbolAtLocation(nodeOrNodes: Node | readonly Node[]): Symbol | (Symbol | undefined)[] | undefined {
         if (Array.isArray(nodeOrNodes)) {
-            const data = this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsAtLocations", {
+            const data = this.client.apiRequest("getSymbolsAtLocations", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 locations: nodeOrNodes.map(node => getNodeId(node)),
             });
             return data.map(d => d ? this.objectRegistry.getOrCreateSymbol(d) : undefined);
         }
-        const data = this.client.apiRequest<SymbolResponse | null>("getSymbolAtLocation", {
+        const data = this.client.apiRequest("getSymbolAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(nodeOrNodes as Node),
@@ -1269,7 +1327,7 @@ export class Checker {
     getSymbolAtPosition(file: DocumentIdentifier, positions: readonly number[]): (Symbol | undefined)[];
     getSymbolAtPosition(file: DocumentIdentifier, positionOrPositions: number | readonly number[]): Symbol | (Symbol | undefined)[] | undefined {
         if (typeof positionOrPositions === "number") {
-            const data = this.client.apiRequest<SymbolResponse | null>("getSymbolAtPosition", {
+            const data = this.client.apiRequest("getSymbolAtPosition", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 file,
@@ -1277,7 +1335,7 @@ export class Checker {
             });
             return data ? this.objectRegistry.getOrCreateSymbol(data) : undefined;
         }
-        const data = this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsAtPositions", {
+        const data = this.client.apiRequest("getSymbolsAtPositions", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1290,14 +1348,14 @@ export class Checker {
     getSymbolOfSourceFile(files: readonly DocumentIdentifier[]): (Symbol | undefined)[];
     getSymbolOfSourceFile(fileOrFiles: DocumentIdentifier | readonly DocumentIdentifier[]): Symbol | (Symbol | undefined)[] | undefined {
         if (Array.isArray(fileOrFiles)) {
-            const data = this.client.apiRequest<(SymbolResponse | null)[]>("getSymbolsOfSourceFiles", {
+            const data = this.client.apiRequest("getSymbolsOfSourceFiles", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 files: fileOrFiles,
             });
             return data.map(d => d ? this.objectRegistry.getOrCreateSymbol(d) : undefined);
         }
-        const data = this.client.apiRequest<SymbolResponse | null>("getSymbolOfSourceFile", {
+        const data = this.client.apiRequest("getSymbolOfSourceFile", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file: fileOrFiles as DocumentIdentifier,
@@ -1314,14 +1372,14 @@ export class Checker {
     getTypeOfSymbol(symbols: readonly Symbol[]): Type[];
     getTypeOfSymbol(symbolOrSymbols: Symbol | readonly Symbol[]): Type | Type[] {
         if (Array.isArray(symbolOrSymbols)) {
-            const data = this.client.apiRequest<TypeResponse[]>("getTypesOfSymbols", {
+            const data = this.client.apiRequest("getTypesOfSymbols", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 symbols: symbolOrSymbols.map(s => s.id),
             });
             return data.map(d => this.objectRegistry.getOrCreateType(d));
         }
-        const data = this.client.apiRequest<TypeResponse>("getTypeOfSymbol", {
+        const data = this.client.apiRequest("getTypeOfSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: (symbolOrSymbols as Symbol).id,
@@ -1335,7 +1393,7 @@ export class Checker {
      * {@link Type.isErrorType} to detect it).
      */
     getDeclaredTypeOfSymbol(symbol: Symbol): Type {
-        const data = this.client.apiRequest<TypeResponse>("getDeclaredTypeOfSymbol", {
+        const data = this.client.apiRequest("getDeclaredTypeOfSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1344,7 +1402,7 @@ export class Checker {
     }
 
     getReferencesToSymbolInFile(file: DocumentIdentifier, symbol: Symbol): NodeHandle[] {
-        const data = this.client.apiRequest<string[] | null>("getReferencesToSymbolInFile", {
+        const data = this.client.apiRequest("getReferencesToSymbolInFile", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1377,14 +1435,14 @@ export class Checker {
     getTypeAtLocation(nodes: readonly Node[]): Type[];
     getTypeAtLocation(nodeOrNodes: Node | readonly Node[]): Type | Type[] {
         if (Array.isArray(nodeOrNodes)) {
-            const data = this.client.apiRequest<TypeResponse[]>("getTypeAtLocations", {
+            const data = this.client.apiRequest("getTypeAtLocations", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 locations: nodeOrNodes.map(node => getNodeId(node)),
             });
             return data.map(d => this.objectRegistry.getOrCreateType(d));
         }
-        const data = this.client.apiRequest<TypeResponse>("getTypeAtLocation", {
+        const data = this.client.apiRequest("getTypeAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(nodeOrNodes as Node),
@@ -1402,7 +1460,7 @@ export class Checker {
      * signature (use {@link Checker.isUnknownSignature} to detect it).
      */
     getResolvedSignature(node: Node): Signature {
-        const data = this.client.apiRequest<SignatureResponse>("getResolvedSignature", {
+        const data = this.client.apiRequest("getResolvedSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1414,7 +1472,7 @@ export class Checker {
     getTypeAtPosition(file: DocumentIdentifier, positions: readonly number[]): (Type | undefined)[];
     getTypeAtPosition(file: DocumentIdentifier, positionOrPositions: number | readonly number[]): Type | (Type | undefined)[] | undefined {
         if (typeof positionOrPositions === "number") {
-            const data = this.client.apiRequest<TypeResponse | null>("getTypeAtPosition", {
+            const data = this.client.apiRequest("getTypeAtPosition", {
                 snapshot: this.snapshotId,
                 project: this.project.id,
                 file,
@@ -1422,7 +1480,7 @@ export class Checker {
             });
             return data ? this.objectRegistry.getOrCreateType(data) : undefined;
         }
-        const data = this.client.apiRequest<(TypeResponse | null)[]>("getTypesAtPositions", {
+        const data = this.client.apiRequest("getTypesAtPositions", {
             snapshot: this.snapshotId,
             project: this.project.id,
             file,
@@ -1439,15 +1497,19 @@ export class Checker {
     ): Symbol | undefined {
         // Distinguish Node (has `kind`) from DocumentPosition (has `document` and `position`)
         const isNode = location && "kind" in location;
-        const data = this.client.apiRequest<SymbolResponse | null>("resolveName", {
+        const data = this.client.apiRequest("resolveName", {
             snapshot: this.snapshotId,
             project: this.project.id,
             name,
             meaning,
-            location: isNode ? getNodeId(location as Node) : undefined,
-            file: !isNode && location ? (location as DocumentPosition).document : undefined,
-            position: !isNode && location ? (location as DocumentPosition).position : undefined,
-            excludeGlobals,
+            ...(isNode ? { location: getNodeId(location as Node) } : {}),
+            ...(!isNode && location
+                ? {
+                    file: (location as DocumentPosition).document,
+                    position: (location as DocumentPosition).position,
+                }
+                : {}),
+            ...(excludeGlobals !== undefined ? { excludeGlobals } : {}),
         });
         return data ? this.objectRegistry.getOrCreateSymbol(data) : undefined;
     }
@@ -1458,13 +1520,16 @@ export class Checker {
     getSymbolsInScope(location: Node | DocumentPosition, meaning: SymbolFlags): readonly Symbol[] {
         // Distinguish Node (has `kind`) from DocumentPosition (has `document` and `position`)
         const isNode = "kind" in location;
-        const data = this.client.apiRequest<SymbolResponse[] | null>("getSymbolsInScope", {
+        const data = this.client.apiRequest("getSymbolsInScope", {
             snapshot: this.snapshotId,
             project: this.project.id,
             meaning,
-            location: isNode ? getNodeId(location as Node) : undefined,
-            file: isNode ? undefined : (location as DocumentPosition).document,
-            position: isNode ? undefined : (location as DocumentPosition).position,
+            ...(isNode
+                ? { location: getNodeId(location as Node) }
+                : {
+                    file: (location as DocumentPosition).document,
+                    position: (location as DocumentPosition).position,
+                }),
         });
         return data ? data.map(d => this.objectRegistry.getOrCreateSymbol(d)) : [];
     }
@@ -1476,7 +1541,7 @@ export class Checker {
     }
 
     getContextualType(node: Expression): Type | undefined {
-        const data = this.client.apiRequest<TypeResponse | null>("getContextualType", {
+        const data = this.client.apiRequest("getContextualType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1486,7 +1551,7 @@ export class Checker {
 
     /** Get the base type of a literal type (e.g. `number` for `42`). Always returns a type. */
     getBaseTypeOfLiteralType(type: Type): Type {
-        const data = this.client.apiRequest<TypeResponse>("getBaseTypeOfLiteralType", {
+        const data = this.client.apiRequest("getBaseTypeOfLiteralType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1505,7 +1570,7 @@ export class Checker {
      * {@link Type.isErrorType} to detect it).
      */
     getTypeFromTypeNode(node: TypeNode): Type {
-        const data = this.client.apiRequest<TypeResponse>("getTypeFromTypeNode", {
+        const data = this.client.apiRequest("getTypeFromTypeNode", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1515,7 +1580,7 @@ export class Checker {
 
     /** Get the widened type. Always returns a type. */
     getWidenedType(type: Type): Type {
-        const data = this.client.apiRequest<TypeResponse>("getWidenedType", {
+        const data = this.client.apiRequest("getWidenedType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1528,7 +1593,7 @@ export class Checker {
      * returns a type; an out-of-range index yields the `any` type.
      */
     getParameterType(signature: Signature, index: number): Type {
-        const data = this.client.apiRequest<TypeResponse>("getParameterType", {
+        const data = this.client.apiRequest("getParameterType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1538,7 +1603,7 @@ export class Checker {
     }
 
     isArrayLikeType(type: Type): boolean {
-        return this.client.apiRequest<boolean>("isArrayLikeType", {
+        return this.client.apiRequest("isArrayLikeType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1546,7 +1611,7 @@ export class Checker {
     }
 
     isTypeAssignableTo(source: Type, target: Type): boolean {
-        return this.client.apiRequest<boolean>("isTypeAssignableTo", {
+        return this.client.apiRequest("isTypeAssignableTo", {
             snapshot: this.snapshotId,
             project: this.project.id,
             source: source.id,
@@ -1555,7 +1620,7 @@ export class Checker {
     }
 
     getShorthandAssignmentValueSymbol(node: Node): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getShorthandAssignmentValueSymbol", {
+        const data = this.client.apiRequest("getShorthandAssignmentValueSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1569,7 +1634,7 @@ export class Checker {
      * error type (use {@link Type.isErrorType} to detect it).
      */
     getTypeOfSymbolAtLocation(symbol: Symbol, location: Node): Type {
-        const data = this.client.apiRequest<TypeResponse>("getTypeOfSymbolAtLocation", {
+        const data = this.client.apiRequest("getTypeOfSymbolAtLocation", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1578,8 +1643,8 @@ export class Checker {
         return this.objectRegistry.getOrCreateType(data);
     }
 
-    private getIntrinsicType(method: string): Type {
-        const data = this.client.apiRequest<TypeResponse>(method, {
+    private getIntrinsicType(method: IntrinsicTypeMethod): Type {
+        const data = this.client.apiRequest(method, {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1628,8 +1693,8 @@ export class Checker {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
         if (!binaryData) return undefined;
         return decodeNode(binaryData) as TypeNode;
@@ -1641,25 +1706,27 @@ export class Checker {
             project: this.project.id,
             signature: signature.id,
             kind,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
         if (!binaryData) return undefined;
         return decodeNode(binaryData) as Node;
     }
 
     typeToString(type: Type, enclosingDeclaration?: Node, flags?: number): string {
-        return this.client.apiRequest<string>("typeToString", {
+        const result = this.client.apiRequest("typeToString", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
-            location: enclosingDeclaration ? getNodeId(enclosingDeclaration) : undefined,
-            flags,
+            ...(enclosingDeclaration ? { location: getNodeId(enclosingDeclaration) } : {}),
+            ...(flags !== undefined ? { flags } : {}),
         });
+        if (typeof result !== "string") throw new TypeError("typeToString returned a non-string result");
+        return result;
     }
 
     isContextSensitive(node: Node): boolean {
-        return this.client.apiRequest<boolean>("isContextSensitive", {
+        return this.client.apiRequest("isContextSensitive", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1667,7 +1734,7 @@ export class Checker {
     }
 
     isArrayType(type: Type): boolean {
-        return this.client.apiRequest<boolean>("isArrayType", {
+        return this.client.apiRequest("isArrayType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1675,7 +1742,7 @@ export class Checker {
     }
 
     isTupleType(type: Type): boolean {
-        return this.client.apiRequest<boolean>("isTupleType", {
+        return this.client.apiRequest("isTupleType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1692,7 +1759,7 @@ export class Checker {
      * no rest parameter yields the `any` type.
      */
     getRestTypeOfSignature(signature: Signature): Type {
-        const data = this.client.apiRequest<TypeResponse>("getRestTypeOfSignature", {
+        const data = this.client.apiRequest("getRestTypeOfSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1701,7 +1768,7 @@ export class Checker {
     }
 
     getTypePredicateOfSignature(signature: Signature): TypePredicate | undefined {
-        const data = this.client.apiRequest<TypePredicateResponse | null>("getTypePredicateOfSignature", {
+        const data = this.client.apiRequest("getTypePredicateOfSignature", {
             snapshot: this.snapshotId,
             project: this.project.id,
             signature: signature.id,
@@ -1749,7 +1816,7 @@ export class Checker {
     }
 
     getBaseConstraintOfType(type: Type): Type | undefined {
-        const data = this.client.apiRequest<TypeResponse | null>("getBaseConstraintOfType", {
+        const data = this.client.apiRequest("getBaseConstraintOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1758,7 +1825,7 @@ export class Checker {
     }
 
     getPropertyOfType(type: Type, name: string): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getPropertyOfType", {
+        const data = this.client.apiRequest("getPropertyOfType", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1768,17 +1835,17 @@ export class Checker {
     }
 
     getConstantValue(node: Node): string | number | undefined {
-        const data = this.client.apiRequest<string | number | null>("getConstantValue", {
+        const data = this.client.apiRequest("getConstantValue", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
         });
-        return data ?? undefined;
+        return typeof data === "string" || typeof data === "number" ? data : undefined;
     }
 
     /** Get the signature of a function-like declaration. Always returns a signature. */
     getSignatureFromDeclaration(node: Node): Signature {
-        const data = this.client.apiRequest<SignatureResponse>("getSignatureFromDeclaration", {
+        const data = this.client.apiRequest("getSignatureFromDeclaration", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1787,7 +1854,7 @@ export class Checker {
     }
 
     getExportSpecifierLocalTargetSymbol(node: Node): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getExportSpecifierLocalTargetSymbol", {
+        const data = this.client.apiRequest("getExportSpecifierLocalTargetSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             location: getNodeId(node),
@@ -1801,7 +1868,7 @@ export class Checker {
      * {@link Checker.isUnknownSymbol} to detect it).
      */
     getAliasedSymbol(symbol: Symbol): Symbol {
-        const data = this.client.apiRequest<SymbolResponse>("getAliasedSymbol", {
+        const data = this.client.apiRequest("getAliasedSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1814,7 +1881,7 @@ export class Checker {
      * (e.g. `"/path/to/module".Namespace.Name`).
      */
     getFullyQualifiedName(symbol: Symbol): string {
-        return this.client.apiRequest<string>("getFullyQualifiedName", {
+        return this.client.apiRequest("getFullyQualifiedName", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1822,7 +1889,7 @@ export class Checker {
     }
 
     getImmediateAliasedSymbol(symbol: Symbol): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getImmediateAliasedSymbol", {
+        const data = this.client.apiRequest("getImmediateAliasedSymbol", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1837,7 +1904,7 @@ export class Checker {
      * the first call.
      */
     private getWellKnownSymbols(): { unknown: number; undefined: number; arguments: number; } {
-        return this.wellKnownSymbols ??= this.client.apiRequest<{ unknown: number; undefined: number; arguments: number; }>("getWellKnownSymbols", {
+        return this.wellKnownSymbols ??= this.client.apiRequest("getWellKnownSymbols", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1871,7 +1938,7 @@ export class Checker {
      * identity checks against it are local after the first call.
      */
     private getWellKnownSignatures(): { unknown: number; } {
-        return this.wellKnownSignatures ??= this.client.apiRequest<{ unknown: number; }>("getWellKnownSignatures", {
+        return this.wellKnownSignatures ??= this.client.apiRequest("getWellKnownSignatures", {
             snapshot: this.snapshotId,
             project: this.project.id,
         });
@@ -1887,7 +1954,7 @@ export class Checker {
     }
 
     getExportsOfModule(symbol: Symbol): readonly Symbol[] {
-        const data = this.client.apiRequest<SymbolResponse[] | null>("getExportsOfModule", {
+        const data = this.client.apiRequest("getExportsOfModule", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1896,7 +1963,7 @@ export class Checker {
     }
 
     getMemberInModuleExports(symbol: Symbol, name: string): Symbol | undefined {
-        const data = this.client.apiRequest<SymbolResponse | null>("getMemberInModuleExports", {
+        const data = this.client.apiRequest("getMemberInModuleExports", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1906,7 +1973,7 @@ export class Checker {
     }
 
     getJsDocTagsOfSymbol(symbol: Symbol): readonly JSDocTagInfo[] {
-        const data = this.client.apiRequest<JSDocTagInfo[] | null>("getJsDocTags", {
+        const data = this.client.apiRequest("getJsDocTags", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1915,7 +1982,7 @@ export class Checker {
     }
 
     getDocumentationCommentOfSymbol(symbol: Symbol): string {
-        return this.client.apiRequest<string>("getDocumentationComment", {
+        return this.client.apiRequest("getDocumentationComment", {
             snapshot: this.snapshotId,
             project: this.project.id,
             symbol: symbol.id,
@@ -1926,7 +1993,7 @@ export class Checker {
      * Get the type arguments of a type reference (e.g. the `string` in `Array<string>`).
      */
     getTypeArguments(type: TypeReference): readonly Type[] {
-        const data = this.client.apiRequest<TypeResponse[] | null>("getTypeArguments", {
+        const data = this.client.apiRequest("getTypeArguments", {
             snapshot: this.snapshotId,
             project: this.project.id,
             type: type.id,
@@ -1951,9 +2018,11 @@ export class Emitter {
     printNode(node: Node, options: PrintNodeOptions = {}): string {
         const encoded = encodeNode(node);
         const base64 = uint8ArrayToBase64(encoded);
-        return this.client.apiRequest<string>("printNode", {
+        return this.client.apiRequest("printNode", {
             data: base64,
-            ...options,
+            ...(options.preserveSourceNewlines !== undefined ? { preserveSourceNewlines: options.preserveSourceNewlines } : {}),
+            ...(options.neverAsciiEscape !== undefined ? { neverAsciiEscape: options.neverAsciiEscape } : {}),
+            ...(options.terminateUnterminatedLiterals !== undefined ? { terminateUnterminatedLiterals: options.terminateUnterminatedLiterals } : {}),
         });
     }
 }
@@ -1977,7 +2046,7 @@ export class SnapshotInternalAPI {
      * @returns The formatted text of the node, indented for the insertion position.
      */
     formatNodeForInsertion(node: Node, file: DocumentIdentifier, position: number): string {
-        const data = this.client.apiRequest<ProjectResponse | null>("getDefaultProjectForFile", {
+        const data = this.client.apiRequest("getDefaultProjectForFile", {
             snapshot: this.snapshotId,
             file,
         });
@@ -1987,7 +2056,7 @@ export class SnapshotInternalAPI {
 
         const encoded = encodeNode(node);
         const base64 = uint8ArrayToBase64(encoded);
-        return this.client.apiRequest<string>("formatNodeForInsertion", {
+        return this.client.apiRequest("formatNodeForInsertion", {
             snapshot: this.snapshotId,
             project: data.id,
             file,
@@ -2075,11 +2144,11 @@ export class Symbol {
         this.objectRegistry = objectRegistry;
 
         this.id = data.id;
-        this.escapedName = data.name;
-        this.name = unescapeLeadingUnderscores(data.name);
+        this.escapedName = data.name as __String;
+        this.name = unescapeLeadingUnderscores(data.name as __String);
         this.flags = data.flags;
         this.checkFlags = data.checkFlags;
-        const canonicalProject = objectRegistry.getProject(data.project);
+        const canonicalProject = objectRegistry.getProject(data.project as Path);
         if (!canonicalProject) {
             throw new Error(`Symbol ${data.id} references unknown canonical project '${data.project}'`);
         }
@@ -2111,7 +2180,7 @@ export class Symbol {
         return this.exportsCache ??= this.fetchSymbolTable("getExportsOfSymbol");
     }
 
-    private fetchSymbolTable(method: string): ReadonlyMap<__String, Symbol> {
+    private fetchSymbolTable(method: SymbolsPropertyMethod): ReadonlyMap<__String, Symbol> {
         const symbols = this.objectRegistry.fetchSymbols(this, method, undefined, this.canonicalProject.id);
         const table = new Map<__String, Symbol>();
         for (const symbol of symbols) {
@@ -2195,7 +2264,8 @@ class TypeObject implements Type {
         if (data.value != null) {
             // BigInt literal values are serialized as decimal strings (e.g. "-123") because
             // JSON cannot represent bigint. Decode them back into a real bigint here.
-            this.value = (data.flags & TypeFlags.BigIntLiteral) ? BigInt(data.value) : data.value;
+            const value = data.value as string | number | boolean;
+            this.value = (data.flags & TypeFlags.BigIntLiteral) ? BigInt(value as string) : value;
         }
         if (data.intrinsicName !== undefined) this.intrinsicName = data.intrinsicName;
         if (data.isThisType !== undefined) this.isThisType = data.isThisType;
diff --git a/_packages/native-preview/src/api/sync/client.ts b/_packages/native-preview/src/api/sync/client.ts
index 615fc299fa7..d1f25008acf 100644
--- a/_packages/native-preview/src/api/sync/client.ts
+++ b/_packages/native-preview/src/api/sync/client.ts
@@ -7,6 +7,10 @@ import {
     isSpawnOptions,
     resolveExePath,
 } from "../options.ts";
+import type {
+    APIMethodInfo,
+    SourceFileResponseMethod,
+} from "../proto.ts";
 import { SyncRpcChannel } from "../syncChannel.ts";
 import {
     combineTimingInfo,
@@ -81,18 +85,18 @@ export class Client {
         }
     }
 
-    apiRequest<T>(method: string, params?: unknown): T {
+    apiRequest<K extends keyof APIMethodInfo>(method: K, params?: APIMethodInfo[K]["params"]): APIMethodInfo[K]["result"] {
         const encodedPayload = JSON.stringify(params);
         const start = performance.now();
         const result = this.channel.requestSync(method, encodedPayload);
         this.recordTiming(method, start);
         if (result.length) {
-            return JSON.parse(result) as T;
+            return JSON.parse(result) as APIMethodInfo[K]["result"];
         }
-        return undefined as unknown as T;
+        return undefined as APIMethodInfo[K]["result"];
     }
 
-    apiRequestBinary(method: string, params?: unknown): Uint8Array | undefined {
+    apiRequestBinary<K extends SourceFileResponseMethod>(method: K, params?: APIMethodInfo[K]["params"]): Uint8Array | undefined {
         const start = performance.now();
         const result = this.channel.requestBinarySync(method, this.encoder.encode(JSON.stringify(params)));
         this.recordTiming(method, start);
diff --git a/_packages/native-preview/test/compilerOptions.test.ts b/_packages/native-preview/test/compilerOptions.test.ts
deleted file mode 100644
index a5ddeda3f9f..00000000000
--- a/_packages/native-preview/test/compilerOptions.test.ts
+++ /dev/null
@@ -1,108 +0,0 @@
-import assert from "node:assert";
-import { readFileSync } from "node:fs";
-import {
-    dirname,
-    join,
-} from "node:path";
-import {
-    describe,
-    test,
-} from "node:test";
-import { fileURLToPath } from "node:url";
-
-const testDir = dirname(fileURLToPath(import.meta.url));
-const repoRoot = join(testDir, "..", "..", "..");
-const goOptionsPath = join(repoRoot, "internal", "core", "compileroptions.go");
-const tsOptionsPath = join(testDir, "..", "src", "api", "compilerOptions.ts");
-const exposedInternalOptions = new Set(["configFilePath"]);
-
-/**
- * Extracts the JSON tag names of the fields exposed in the TypeScript API.
- * These are the public, non-deprecated Go fields plus explicitly selected
- * internal fields.
- */
-function getGoApiOptionNames(): Set<string> {
-    const source = readFileSync(goOptionsPath, "utf-8");
-    const structMatch = source.match(/type CompilerOptions struct \{([\s\S]*?)\n\}/);
-    assert.ok(structMatch, "Could not find `type CompilerOptions struct` in compileroptions.go");
-
-    let body = structMatch[1];
-    const internalMarker = body.indexOf("// Internal fields");
-    assert.notStrictEqual(internalMarker, -1, "Could not find `// Internal fields` marker in compileroptions.go");
-    const internalBody = body.slice(internalMarker);
-    body = body.slice(0, internalMarker);
-
-    const names = new Set<string>();
-    let prevDeprecated = false;
-    for (const rawLine of body.split("\n")) {
-        const line = rawLine.trim();
-        if (line === "") continue;
-
-        const tagMatch = line.match(/`json:"([^",]+)/);
-        if (tagMatch) {
-            // A field's `// Deprecated:` doc comment sits on the line directly above it.
-            if (!prevDeprecated) {
-                names.add(tagMatch[1]);
-            }
-            prevDeprecated = false;
-        }
-        else {
-            prevDeprecated = line.startsWith("// Deprecated:");
-        }
-    }
-    for (const match of internalBody.matchAll(/`json:"([^",]+)/g)) {
-        if (exposedInternalOptions.has(match[1])) {
-            names.add(match[1]);
-        }
-    }
-    return names;
-}
-
-/**
- * Extracts the property names of the TS `CompilerOptions` interface.
- */
-function getTsOptionNames(): Set<string> {
-    const source = readFileSync(tsOptionsPath, "utf-8");
-    const interfaceMatch = source.match(/export interface CompilerOptions \{([\s\S]*?)\n\}/);
-    assert.ok(interfaceMatch, "Could not find `export interface CompilerOptions` in compilerOptions.ts");
-
-    const names = new Set<string>();
-    for (const line of interfaceMatch[1].split("\n")) {
-        const propMatch = line.match(/^\s*([A-Za-z_]\w*)\??:/);
-        if (propMatch) {
-            names.add(propMatch[1]);
-        }
-    }
-    return names;
-}
-
-describe("CompilerOptions type stays in sync with Go", () => {
-    const goNames = getGoApiOptionNames();
-    const tsNames = getTsOptionNames();
-
-    test("sanity: both sides parsed a plausible number of options", () => {
-        assert.ok(goNames.size > 50, `Parsed too few Go options (${goNames.size}); parser likely broke`);
-        assert.ok(tsNames.size > 50, `Parsed too few TS options (${tsNames.size}); parser likely broke`);
-    });
-
-    test("no public Go option is missing from the TS interface", () => {
-        const missing = [...goNames].filter(n => !tsNames.has(n)).sort();
-        assert.deepStrictEqual(
-            missing,
-            [],
-            `The following public compiler options exist in internal/core/compileroptions.go but are missing from `
-                + `src/api/compilerOptions.ts. Add them, or, if they are internal, move them after the `
-                + `"// Internal fields" marker (or annotate them with a "// Deprecated:" comment) in the Go struct:\n  ${missing.join("\n  ")}`,
-        );
-    });
-
-    test("no TS option is absent from the public Go struct", () => {
-        const extra = [...tsNames].filter(n => !goNames.has(n)).sort();
-        assert.deepStrictEqual(
-            extra,
-            [],
-            `The following options exist in src/api/compilerOptions.ts but are not public fields of `
-                + `internal/core/compileroptions.go (they may have been removed, renamed, or marked internal):\n  ${extra.join("\n  ")}`,
-        );
-    });
-});
diff --git a/_tools/gen-proto/main.go b/_tools/gen-proto/main.go
new file mode 100644
index 00000000000..4750c788f0f
--- /dev/null
+++ b/_tools/gen-proto/main.go
@@ -0,0 +1,735 @@
+package main
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/types"
+	"os"
+	"path/filepath"
+	"reflect"
+	"slices"
+	"sort"
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/go/packages"
+)
+
+func main() {
+	os.Exit(run())
+}
+
+func run() int {
+	if len(os.Args) != 3 {
+		fmt.Fprintln(os.Stderr, "Usage: gen-proto <input path>.go <output path>.ts")
+		return 1
+	}
+	if err := generate(os.Args[1], os.Args[2]); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return 1
+	}
+	return 0
+}
+
+type methodInfo struct {
+	name           string
+	params         types.Type
+	result         types.Type
+	paramsText     string
+	resultText     string
+	resultNullable bool
+}
+
+func generate(inputPath string, outputPath string) error {
+	absInput, err := filepath.Abs(inputPath)
+	if err != nil {
+		return err
+	}
+
+	cfg := &packages.Config{
+		Mode: packages.NeedName | packages.NeedFiles | packages.NeedCompiledGoFiles |
+			packages.NeedSyntax | packages.NeedTypes | packages.NeedTypesInfo |
+			packages.NeedImports | packages.NeedDeps,
+		Dir: filepath.Dir(absInput),
+	}
+	pkgs, err := packages.Load(cfg, ".")
+	if err != nil {
+		return fmt.Errorf("load API package: %w", err)
+	}
+	if len(pkgs) != 1 {
+		return fmt.Errorf("load API package: expected one package, got %d", len(pkgs))
+	}
+	if packages.PrintErrors(pkgs) != 0 {
+		return errors.New("load API package: package contains errors")
+	}
+	pkg := pkgs[0]
+
+	inputFile := findSyntaxFile(pkg, absInput)
+	if inputFile == nil {
+		return fmt.Errorf("input file %q was not part of package %q", absInput, pkg.PkgPath)
+	}
+
+	methods, methodObjects, err := declaredMethods(pkg, inputFile)
+	if err != nil {
+		return err
+	}
+	resultTypeOverrides, nullableResults, err := discoverResultMetadata(pkg)
+	if err != nil {
+		return err
+	}
+	discoverSessionMethods(pkg, methodObjects, methods, resultTypeOverrides, nullableResults)
+	discoverConnectionMethods(pkg, methodObjects, methods)
+
+	for _, method := range methods {
+		if method.paramsText == "" && method.params == nil {
+			return fmt.Errorf("method %q has no request dispatch", method.name)
+		}
+		if method.resultText == "" && method.result == nil {
+			return fmt.Errorf("method %q has no result type", method.name)
+		}
+	}
+	// release is an ownership notification from the client's perspective. The
+	// server's internal bool acknowledgement is deliberately not part of the API.
+	for _, method := range methods {
+		if method.name == "release" || method.name == "startCPUProfile" {
+			method.result = nil
+			method.resultText = "void"
+		}
+	}
+
+	renderer := newTypeRenderer(pkg)
+	var methodsOut bytes.Buffer
+	methodsOut.WriteString("export type APIMethod<TParams, TResult> = { params: TParams; result: TResult; };\n\n")
+	methodsOut.WriteString("export interface APIMethodInfo {\n")
+	for _, method := range methods {
+		params := method.paramsText
+		if params == "" {
+			params = renderer.requestType(method.params)
+		}
+		result := method.resultText
+		if result == "" {
+			result = renderer.resultType(method.result, method.resultNullable)
+		}
+		fmt.Fprintf(&methodsOut, "    %s: APIMethod<%s, %s>;\n", propertyName(method.name), params, result)
+	}
+	methodsOut.WriteString("}\n")
+
+	declarations, err := renderer.declarations()
+	if err != nil {
+		return err
+	}
+	var out bytes.Buffer
+	out.WriteString("// Code generated by gen-proto; DO NOT EDIT.\n\n")
+	if imports := renderer.importDeclarations(); imports != "" {
+		out.WriteString(imports)
+		out.WriteString("\n")
+	}
+	out.Write(methodsOut.Bytes())
+	if declarations != "" {
+		out.WriteString("\n")
+		out.WriteString(declarations)
+	}
+
+	absOutput, err := filepath.Abs(outputPath)
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(absOutput), 0o755); err != nil {
+		return err
+	}
+	data := bytes.ReplaceAll(out.Bytes(), []byte{'\n'}, []byte{'\r', '\n'})
+	if err := os.WriteFile(absOutput, data, 0o644); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	return nil
+}
+
+func findSyntaxFile(pkg *packages.Package, path string) *ast.File {
+	cleanPath := filepath.Clean(path)
+	for i, filePath := range pkg.CompiledGoFiles {
+		if filepath.Clean(filePath) == cleanPath {
+			return pkg.Syntax[i]
+		}
+	}
+	return nil
+}
+
+func declaredMethods(pkg *packages.Package, file *ast.File) ([]*methodInfo, map[types.Object]*methodInfo, error) {
+	var methods []*methodInfo
+	methodObjects := make(map[types.Object]*methodInfo)
+	for _, decl := range file.Decls {
+		genDecl, ok := decl.(*ast.GenDecl)
+		if !ok || genDecl.Tok.String() != "const" {
+			continue
+		}
+		for _, spec := range genDecl.Specs {
+			valueSpec := spec.(*ast.ValueSpec)
+			for _, name := range valueSpec.Names {
+				if !strings.HasPrefix(name.Name, "Method") {
+					continue
+				}
+				obj := pkg.TypesInfo.Defs[name]
+				constantObject, ok := obj.(*types.Const)
+				if !ok || constantObject.Val().Kind() != constant.String {
+					return nil, nil, fmt.Errorf("%s is not a string method constant", name.Name)
+				}
+				method := &methodInfo{name: constant.StringVal(constantObject.Val())}
+				methods = append(methods, method)
+				methodObjects[obj] = method
+			}
+		}
+	}
+	return methods, methodObjects, nil
+}
+
+func discoverResultMetadata(pkg *packages.Package) (map[types.Object]types.Type, map[types.Object]bool, error) {
+	const resultDirective = "@gen-proto-result:"
+	const nullableDirective = "@gen-proto-nullable"
+	overrides := make(map[types.Object]types.Type)
+	nullableResults := make(map[types.Object]bool)
+	for _, file := range pkg.Syntax {
+		for _, decl := range file.Decls {
+			fn, ok := decl.(*ast.FuncDecl)
+			if !ok || fn.Doc == nil {
+				continue
+			}
+			fnObject := pkg.TypesInfo.Defs[fn.Name]
+			for _, comment := range fn.Doc.List {
+				text := strings.TrimSpace(strings.TrimPrefix(comment.Text, "//"))
+				if text == nullableDirective {
+					nullableResults[fnObject] = true
+					continue
+				}
+				typeName, ok := strings.CutPrefix(text, resultDirective)
+				if !ok {
+					continue
+				}
+				typeName = strings.TrimSpace(typeName)
+				typeObject, ok := pkg.Types.Scope().Lookup(typeName).(*types.TypeName)
+				if !ok {
+					return nil, nil, fmt.Errorf("result type override on %s refers to unknown type %q", fn.Name.Name, typeName)
+				}
+				overrides[fnObject] = typeObject.Type()
+			}
+		}
+	}
+	return overrides, nullableResults, nil
+}
+
+func discoverSessionMethods(pkg *packages.Package, methodObjects map[types.Object]*methodInfo, methods []*methodInfo, resultTypeOverrides map[types.Object]types.Type, nullableResults map[types.Object]bool) {
+	for _, file := range pkg.Syntax {
+		for _, decl := range file.Decls {
+			fn, isFuncDecl := decl.(*ast.FuncDecl)
+			if !isFuncDecl || fn.Name.Name != "HandleRequest" || fn.Recv == nil || fn.Body == nil {
+				continue
+			}
+			ast.Inspect(fn.Body, func(node ast.Node) bool {
+				clause, isCaseClause := node.(*ast.CaseClause)
+				if !isCaseClause || len(clause.List) != 1 {
+					return true
+				}
+				method := methodForExpression(pkg, methodObjects, clause.List[0])
+				if method == nil {
+					return true
+				}
+
+				method.paramsText = "null"
+				ast.Inspect(clause, func(child ast.Node) bool {
+					assertion, isTypeAssertion := child.(*ast.TypeAssertExpr)
+					if !isTypeAssertion || assertion.Type == nil {
+						return true
+					}
+					if ident, isIdent := assertion.X.(*ast.Ident); isIdent && ident.Name == "parsed" {
+						method.params = pkg.TypesInfo.TypeOf(assertion.Type)
+						method.paramsText = ""
+					}
+					return true
+				})
+
+				for _, stmt := range clause.Body {
+					returnStmt, isReturnStmt := stmt.(*ast.ReturnStmt)
+					if !isReturnStmt || len(returnStmt.Results) == 0 {
+						continue
+					}
+					call, isCall := returnStmt.Results[0].(*ast.CallExpr)
+					if !isCall {
+						continue
+					}
+					sig, isSignature := types.Unalias(pkg.TypesInfo.TypeOf(call.Fun)).(*types.Signature)
+					if isSignature && sig.Results().Len() > 0 {
+						method.result = sig.Results().At(0).Type()
+					}
+					called := calledObject(pkg, call.Fun)
+					if override := resultTypeOverrides[called]; override != nil {
+						method.result = override
+					}
+					method.resultNullable = nullableResults[called]
+				}
+				return false
+			})
+		}
+	}
+
+	for _, method := range methods {
+		if method.params != nil && method.paramsText == "null" {
+			method.paramsText = ""
+		}
+	}
+}
+
+func calledObject(pkg *packages.Package, expr ast.Expr) types.Object {
+	switch expr := expr.(type) {
+	case *ast.Ident:
+		return pkg.TypesInfo.Uses[expr]
+	case *ast.SelectorExpr:
+		if selection := pkg.TypesInfo.Selections[expr]; selection != nil {
+			return selection.Obj()
+		}
+		return pkg.TypesInfo.Uses[expr.Sel]
+	default:
+		return nil
+	}
+}
+
+func discoverConnectionMethods(pkg *packages.Package, methodObjects map[types.Object]*methodInfo, methods []*methodInfo) {
+	missing := make(map[*methodInfo]bool)
+	for _, method := range methods {
+		missing[method] = method.params == nil && method.paramsText == ""
+	}
+	for _, file := range pkg.Syntax {
+		ast.Inspect(file, func(node ast.Node) bool {
+			clause, isCaseClause := node.(*ast.CaseClause)
+			if !isCaseClause || len(clause.List) != 1 {
+				return true
+			}
+			method := methodForExpression(pkg, methodObjects, clause.List[0])
+			if method == nil || !missing[method] {
+				return true
+			}
+			ast.Inspect(clause, func(child ast.Node) bool {
+				call, isCall := child.(*ast.CallExpr)
+				if !isCall || len(call.Args) < 2 {
+					return true
+				}
+				selector, isSelector := call.Fun.(*ast.SelectorExpr)
+				if !isSelector || selector.Sel.Name != "WriteResponse" {
+					return true
+				}
+				method.paramsText = "void"
+				if ident, isIdent := call.Args[1].(*ast.Ident); isIdent && ident.Name == "nil" {
+					method.resultText = "void"
+				} else {
+					method.result = pkg.TypesInfo.TypeOf(call.Args[1])
+				}
+				missing[method] = false
+				return false
+			})
+			return false
+		})
+	}
+}
+
+func methodForExpression(pkg *packages.Package, methodObjects map[types.Object]*methodInfo, expr ast.Expr) *methodInfo {
+	call, ok := expr.(*ast.CallExpr)
+	if ok && len(call.Args) == 1 {
+		expr = call.Args[0]
+	}
+	ident, ok := expr.(*ast.Ident)
+	if !ok {
+		return nil
+	}
+	return methodObjects[pkg.TypesInfo.Uses[ident]]
+}
+
+type typeRenderer struct {
+	apiPackagePath     string
+	queued             []*types.Named
+	seen               map[*types.TypeName]bool
+	names              map[string]*types.TypeName
+	imports            map[string][]string
+	docs               map[types.Object]string
+	packages           map[string]*packages.Package
+	documentIdentifier *types.TypeName
+}
+
+func newTypeRenderer(apiPackage *packages.Package) *typeRenderer {
+	r := &typeRenderer{
+		apiPackagePath: apiPackage.PkgPath,
+		seen:           make(map[*types.TypeName]bool),
+		names:          make(map[string]*types.TypeName),
+		imports:        make(map[string][]string),
+		docs:           make(map[types.Object]string),
+		packages:       make(map[string]*packages.Package),
+	}
+	r.indexPackage(apiPackage)
+	return r
+}
+
+func (r *typeRenderer) indexPackage(pkg *packages.Package) {
+	if r.packages[pkg.PkgPath] != nil {
+		return
+	}
+	r.packages[pkg.PkgPath] = pkg
+	for _, imported := range pkg.Imports {
+		r.indexPackage(imported)
+	}
+	for _, file := range pkg.Syntax {
+		for _, decl := range file.Decls {
+			genDecl, ok := decl.(*ast.GenDecl)
+			if !ok || genDecl.Tok.String() != "type" {
+				continue
+			}
+			for _, spec := range genDecl.Specs {
+				typeSpec := spec.(*ast.TypeSpec)
+				r.recordDoc(pkg.TypesInfo.Defs[typeSpec.Name], firstDoc(typeSpec.Doc, genDecl.Doc))
+				structType, ok := typeSpec.Type.(*ast.StructType)
+				if !ok {
+					continue
+				}
+				for _, field := range structType.Fields.List {
+					for _, name := range field.Names {
+						r.recordDoc(pkg.TypesInfo.Defs[name], firstDoc(field.Doc, field.Comment))
+					}
+				}
+			}
+		}
+	}
+}
+
+func (r *typeRenderer) recordDoc(obj types.Object, doc *ast.CommentGroup) {
+	if obj != nil && doc != nil {
+		r.docs[obj] = strings.TrimSpace(doc.Text())
+	}
+}
+
+func firstDoc(docs ...*ast.CommentGroup) *ast.CommentGroup {
+	for _, doc := range docs {
+		if doc != nil {
+			return doc
+		}
+	}
+	return nil
+}
+
+func (r *typeRenderer) requestType(t types.Type) string {
+	if pointer, ok := types.Unalias(t).(*types.Pointer); ok {
+		t = pointer.Elem()
+	}
+	return r.typeString(t, false)
+}
+
+func (r *typeRenderer) resultType(t types.Type, nullable bool) string {
+	if pointer, ok := types.Unalias(t).(*types.Pointer); ok {
+		t = pointer.Elem()
+	}
+	result := r.typeString(t, false)
+	if nullable {
+		result += " | null"
+	}
+	return result
+}
+
+func (r *typeRenderer) typeString(t types.Type, allowNull bool) string {
+	if t == nil {
+		return "void"
+	}
+	t = types.Unalias(t)
+	var result string
+	switch t := t.(type) {
+	case *types.Basic:
+		result = basicType(t)
+	case *types.Pointer:
+		result = r.typeString(t.Elem(), false)
+	case *types.Slice:
+		result = arrayElement(r.typeString(t.Elem(), false)) + "[]"
+	case *types.Array:
+		result = arrayElement(r.typeString(t.Elem(), false)) + "[]"
+	case *types.Map:
+		result = fmt.Sprintf("Record<string, %s>", r.typeString(t.Elem(), true))
+	case *types.Interface:
+		result = "unknown"
+	case *types.Struct:
+		result = r.inlineStruct(t)
+	case *types.Named:
+		result = r.namedType(t)
+	default:
+		result = "unknown"
+	}
+	if allowNull && result != "unknown" {
+		switch t.(type) {
+		case *types.Pointer, *types.Slice, *types.Map:
+			return result + " | null"
+		}
+	}
+	return result
+}
+
+func basicType(t *types.Basic) string {
+	switch {
+	case t.Info()&types.IsBoolean != 0:
+		return "boolean"
+	case t.Info()&(types.IsInteger|types.IsFloat|types.IsComplex) != 0:
+		return "number"
+	case t.Info()&types.IsString != 0:
+		return "string"
+	case t.Kind() == types.UntypedNil:
+		return "null"
+	default:
+		return "unknown"
+	}
+}
+
+func (r *typeRenderer) namedType(named *types.Named) string {
+	obj := named.Obj()
+	qualifiedName := obj.Pkg().Path() + "." + obj.Name()
+	switch qualifiedName {
+	case r.apiPackagePath + ".DocumentIdentifier":
+		r.documentIdentifier = obj
+		return "DocumentIdentifier"
+	case "github.com/microsoft/typescript-go/internal/packagejson.JSONValue":
+		return "unknown"
+	case "github.com/microsoft/typescript-go/internal/core.Tristate":
+		return "boolean"
+	case "github.com/microsoft/typescript-go/internal/core.JsxEmit":
+		return r.importType("JsxEmit", "#enums/jsxEmit")
+	case "github.com/microsoft/typescript-go/internal/core.ModuleDetectionKind":
+		return r.importType("ModuleDetectionKind", "#enums/moduleDetectionKind")
+	case "github.com/microsoft/typescript-go/internal/core.ModuleKind":
+		return r.importType("ModuleKind", "#enums/moduleKind")
+	case "github.com/microsoft/typescript-go/internal/core.ModuleResolutionKind":
+		return r.importType("ModuleResolutionKind", "#enums/moduleResolutionKind")
+	case "github.com/microsoft/typescript-go/internal/core.NewLineKind":
+		return r.importType("NewLineKind", "#enums/newLineKind")
+	case "github.com/microsoft/typescript-go/internal/core.ScriptTarget":
+		return r.importType("ScriptTarget", "#enums/scriptTarget")
+	case "github.com/microsoft/typescript-go/internal/collections.OrderedMap":
+		if named.TypeArgs().Len() != 2 {
+			return "Record<string, unknown>"
+		}
+		return fmt.Sprintf("Record<string, %s>", r.typeString(named.TypeArgs().At(1), false))
+	}
+	if _, ok := named.Underlying().(*types.Struct); !ok {
+		if literals := r.stringLiterals(named); len(literals) > 0 {
+			return strings.Join(literals, " | ")
+		}
+		return r.typeString(named.Underlying(), false)
+	}
+	tsName := exportedName(obj.Name())
+	if previous := r.names[tsName]; previous != nil && previous != obj {
+		panic(fmt.Sprintf("TypeScript name collision between %s and %s", previous, obj))
+	}
+	r.names[tsName] = obj
+	if !r.seen[obj] {
+		r.seen[obj] = true
+		r.queued = append(r.queued, named)
+	}
+	return tsName
+}
+
+func (r *typeRenderer) stringLiterals(named *types.Named) []string {
+	if basic, ok := named.Underlying().(*types.Basic); !ok || basic.Info()&types.IsString == 0 {
+		return nil
+	}
+	pkg := r.packages[named.Obj().Pkg().Path()]
+	if pkg == nil {
+		return nil
+	}
+	var literals []string
+	for _, name := range pkg.Types.Scope().Names() {
+		constantObject, ok := pkg.Types.Scope().Lookup(name).(*types.Const)
+		if !ok || constantObject.Val().Kind() != constant.String || !types.Identical(constantObject.Type(), named) {
+			continue
+		}
+		literal := strconv.Quote(constant.StringVal(constantObject.Val()))
+		if !slices.Contains(literals, literal) {
+			literals = append(literals, literal)
+		}
+	}
+	sort.Strings(literals)
+	return literals
+}
+
+func (r *typeRenderer) inlineStruct(structType *types.Struct) string {
+	var fields []string
+	multiline := false
+	for i := range structType.NumFields() {
+		field, include, optional, nonnil, deprecated, internal := jsonField(structType, i)
+		if !include || deprecated || internal {
+			continue
+		}
+		fieldType := r.typeString(structType.Field(i).Type(), !optional && !nonnil)
+		doc := r.docs[structType.Field(i)]
+		multiline = multiline || doc != ""
+		fields = append(fields, fmt.Sprintf("%s%s%s: %s", inlineDoc(doc), propertyName(field), optionalMarker(optional), fieldType))
+	}
+	if len(fields) == 0 {
+		return "Record<string, never>"
+	}
+	if multiline {
+		return "{\n" + strings.Join(fields, ";\n") + ";\n}"
+	}
+	return "{ " + strings.Join(fields, "; ") + "; }"
+}
+
+func inlineDoc(doc string) string {
+	if doc == "" {
+		return ""
+	}
+	doc = strings.ReplaceAll(doc, "*/", "*\\/")
+	return "/** " + jsDocLine(strings.Join(strings.Fields(doc), " ")) + " */\n"
+}
+
+func (r *typeRenderer) declarations() (string, error) {
+	var out bytes.Buffer
+	if strings.Contains(strings.Join(r.referencedNames(), ","), "DocumentIdentifier") {
+		writeDoc(&out, "", r.docs[r.documentIdentifier])
+		out.WriteString("export type DocumentIdentifier = string | { uri: string; };\n\n")
+	}
+	for len(r.queued) > 0 {
+		named := r.queued[0]
+		r.queued = r.queued[1:]
+		structType := named.Underlying().(*types.Struct)
+		isParams := strings.HasSuffix(named.Obj().Name(), "Params")
+		writeDoc(&out, "", r.docs[named.Obj()])
+		fmt.Fprintf(&out, "export interface %s {\n", exportedName(named.Obj().Name()))
+		for i := range structType.NumFields() {
+			field, include, optional, nonnil, deprecated, internal := jsonField(structType, i)
+			if !include || deprecated || internal {
+				continue
+			}
+			fieldType := r.typeString(structType.Field(i).Type(), !optional && !nonnil)
+			if isParams && isArrayType(structType.Field(i).Type()) {
+				fieldType = "readonly " + fieldType
+			}
+			writeDoc(&out, "    ", r.docs[structType.Field(i)])
+			fmt.Fprintf(&out, "    %s%s: %s;\n", propertyName(field), optionalMarker(optional), fieldType)
+		}
+		out.WriteString("}\n\n")
+	}
+	return strings.TrimRight(out.String(), "\n") + "\n", nil
+}
+
+func writeDoc(out *bytes.Buffer, indent string, doc string) {
+	if doc == "" {
+		return
+	}
+	doc = strings.ReplaceAll(doc, "*/", "*\\/")
+	lines := strings.Split(doc, "\n")
+	if len(lines) == 1 {
+		fmt.Fprintf(out, "%s/** %s */\n", indent, jsDocLine(lines[0]))
+		return
+	}
+	fmt.Fprintf(out, "%s/**\n", indent)
+	for _, line := range lines {
+		fmt.Fprintf(out, "%s * %s\n", indent, jsDocLine(line))
+	}
+	fmt.Fprintf(out, "%s */\n", indent)
+}
+
+func jsDocLine(line string) string {
+	if after, ok := strings.CutPrefix(line, "Deprecated:"); ok {
+		return "@deprecated" + after
+	}
+	return line
+}
+
+func (r *typeRenderer) importDeclarations() string {
+	var out bytes.Buffer
+	paths := make([]string, 0, len(r.imports))
+	for path := range r.imports {
+		paths = append(paths, path)
+	}
+	sort.Strings(paths)
+	for _, path := range paths {
+		names := r.imports[path]
+		sort.Strings(names)
+		fmt.Fprintf(&out, "import type { %s } from %q;\n", strings.Join(names, ", "), path)
+	}
+	return out.String()
+}
+
+func (r *typeRenderer) importType(name string, path string) string {
+	if !slices.Contains(r.imports[path], name) {
+		r.imports[path] = append(r.imports[path], name)
+	}
+	return name
+}
+
+func (r *typeRenderer) referencedNames() []string {
+	names := make([]string, 0, len(r.names)+1)
+	for name := range r.names {
+		names = append(names, name)
+	}
+	// DocumentIdentifier is represented specially and is not in names.
+	names = append(names, "DocumentIdentifier")
+	sort.Strings(names)
+	return names
+}
+
+func jsonField(structType *types.Struct, index int) (name string, include bool, optional bool, nonnil bool, deprecated bool, internal bool) {
+	field := structType.Field(index)
+	if !field.Exported() {
+		return "", false, false, false, false, false
+	}
+	tag := reflect.StructTag(structType.Tag(index)).Get("json")
+	noniltag := reflect.StructTag(structType.Tag(index)).Get("nonnil")
+	deprecatedtag := reflect.StructTag(structType.Tag(index)).Get("deprecated")
+	internaltag := reflect.StructTag(structType.Tag(index)).Get("internal")
+	parts := strings.Split(tag, ",")
+	name = parts[0]
+	if name == "-" {
+		return "", false, false, noniltag == "true", deprecatedtag == "true", internaltag == "true"
+	}
+	if name == "" {
+		name = field.Name()
+	}
+	for _, option := range parts[1:] {
+		if option == "omitempty" || option == "omitzero" {
+			optional = true
+		}
+	}
+	return name, true, optional, noniltag == "true", deprecatedtag == "true", internaltag == "true"
+}
+
+func exportedName(value string) string {
+	if value == "" {
+		return value
+	}
+	return strings.ToUpper(value[:1]) + value[1:]
+}
+
+func optionalMarker(optional bool) string {
+	if optional {
+		return "?"
+	}
+	return ""
+}
+
+func propertyName(name string) string {
+	for i, char := range name {
+		if (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || char == '_' || char == '$' || (i > 0 && char >= '0' && char <= '9') {
+			continue
+		}
+		return strconv.Quote(name)
+	}
+	return name
+}
+
+func arrayElement(element string) string {
+	if strings.Contains(element, " | ") {
+		return "(" + element + ")"
+	}
+	return element
+}
+
+func isArrayType(t types.Type) bool {
+	switch types.Unalias(t).(type) {
+	case *types.Array, *types.Slice:
+		return true
+	default:
+		return false
+	}
+}
diff --git a/_tools/gen-proto/main_test.go b/_tools/gen-proto/main_test.go
new file mode 100644
index 00000000000..3ad1017ef5a
--- /dev/null
+++ b/_tools/gen-proto/main_test.go
@@ -0,0 +1,105 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestGenerate(t *testing.T) {
+	t.Parallel()
+
+	repoRoot := filepath.Clean(filepath.Join("..", ".."))
+	input := filepath.Join(repoRoot, "internal", "api", "proto.go")
+	output := filepath.Join(t.TempDir(), "proto.generated.ts")
+
+	err := generate(input, output)
+	if err != nil {
+		t.Fatal(err)
+	}
+	first, err := os.ReadFile(output)
+	if err != nil {
+		t.Fatal(err)
+	}
+	generated := strings.ReplaceAll(string(first), "\r\n", "\n")
+
+	for _, expected := range []string{
+		`release: APIMethod<ReleaseParams, void>;`,
+		`updateSnapshot: APIMethod<UpdateSnapshotParams, UpdateSnapshotResponse>;`,
+		`initialize: APIMethod<null, InitializeResponse>;`,
+		`export type DocumentIdentifier = string | { uri: string; };`,
+		`export interface ReleaseParams`,
+		`export interface UpdateSnapshotParams`,
+		`openProjects?: readonly DocumentIdentifier[];`,
+		`snapshot: number;`,
+		`file: DocumentIdentifier;`,
+		`import type { JsxEmit } from "#enums/jsxEmit";`,
+		`import type { ModuleDetectionKind } from "#enums/moduleDetectionKind";`,
+		`import type { ModuleKind } from "#enums/moduleKind";`,
+		`import type { ModuleResolutionKind } from "#enums/moduleResolutionKind";`,
+		`import type { NewLineKind } from "#enums/newLineKind";`,
+		`import type { ScriptTarget } from "#enums/scriptTarget";`,
+		`jsx?: JsxEmit;`,
+		`module?: ModuleKind;`,
+		`moduleResolution?: ModuleResolutionKind;`,
+		`moduleDetection?: ModuleDetectionKind;`,
+		`newLine?: NewLineKind;`,
+		`paths?: Record<string, string[]>;`,
+		`target?: ScriptTarget;`,
+		`/** InitializeResponse is returned by the initialize method. */
+export interface InitializeResponse`,
+		`/** UseCaseSensitiveFileNames indicates whether the host file system is case-sensitive. */
+    useCaseSensitiveFileNames: boolean;`,
+		`/** CompilerOptions contains the compiler options exposed by the API. */
+export interface CompilerOptions`,
+		`projectReferences?: ProjectReference[];`,
+		`errors: DiagnosticResponse[];`,
+		`getSymbolsAtPositions: APIMethod<GetSymbolsAtPositionsParams, SymbolResponse[]>;`,
+		`getContextualType: APIMethod<GetContextualTypeParams, TypeResponse | null>;`,
+		`getTypePredicateOfSignature: APIMethod<CheckerSignatureParams, TypePredicateResponse | null>;`,
+		`getTypeParametersOfType: APIMethod<GetTypePropertyParams, TypeResponse[] | null>;`,
+		`getTypeOfSymbol: APIMethod<GetTypeOfSymbolParams, TypeResponse>;`,
+		`getSourceFile: APIMethod<GetSourceFileParams, SourceFileResponse | null>;`,
+		`getConfigSourceFile: APIMethod<GetSourceFileParams, SourceFileResponse | null>;`,
+		`typeToTypeNode: APIMethod<TypeToTypeNodeParams, SourceFileResponse | null>;`,
+		`signatureToSignatureDeclaration: APIMethod<SignatureToSignatureDeclarationParams, SourceFileResponse | null>;`,
+		`export interface SourceFileResponse {
+    /** Data is the base64-encoded binary AST data in the encoder's format. */
+    data: string;
+}`,
+		`projects: ProjectResponse[];`,
+		`entries: CompletionEntryResponse[];`,
+		`outputFiles: EmitOutputFile[];`,
+		`/** Path is a normalized path on disk. */
+    path: string;`,
+		`/** Snapshot is the current client snapshot on which to layer the temporary update. */
+    snapshot: number;`,
+		`kind: "importSymbol";`,
+	} {
+		if !strings.Contains(generated, expected) {
+			t.Errorf("generated output does not contain %q", expected)
+		}
+	}
+	if strings.Contains(generated, "snapshot: number | null;") {
+		t.Error("required numeric fields must not be nullable")
+	}
+	if strings.Contains(generated, " | null)[]") {
+		t.Error("list elements must not be nullable")
+	}
+	if strings.Contains(generated, "projects: readonly ProjectResponse[];") {
+		t.Error("response array fields must remain mutable")
+	}
+
+	err = generate(input, output)
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := os.ReadFile(output)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(first) != string(second) {
+		t.Error("generation is not deterministic")
+	}
+}
diff --git a/internal/api/proto.go b/internal/api/proto.go
index c7a45330b7a..b0578d1b591 100644
--- a/internal/api/proto.go
+++ b/internal/api/proto.go
@@ -1,5 +1,7 @@
 package api
 
+//go:generate npx hereby generate:api
+
 import (
 	"errors"
 	"fmt"
@@ -59,17 +61,6 @@ func parseProjectHandle(handle ProjectID) tspath.Path {
 const (
 	MethodRelease Method = "release"
 
-	// MethodGetServerTiming retrieves the server's collected per-request
-	// processing-time totals and recent-request ring buffer. It is handled by
-	// the connection itself (not the session) and is not recorded in the timing
-	// it reports.
-	MethodGetServerTiming Method = "getServerTiming"
-
-	// MethodResetServerTiming clears the server's collected timing totals and
-	// recent-request ring buffer. Like MethodGetServerTiming, it is handled by
-	// the connection itself and is not recorded.
-	MethodResetServerTiming Method = "resetServerTiming"
-
 	MethodInitialize                   Method = "initialize"
 	MethodUpdateSnapshot               Method = "updateSnapshot"
 	MethodUpdateTemporarySnapshot      Method = "updateTemporarySnapshot"
@@ -242,6 +233,16 @@ type InitializeResponse struct {
 
 // DocumentIdentifier identifies a document by either a file name (plain string) or a URI object.
 // On the wire it is string | { uri: string }.
+//
+// @example
+//
+// Using a file name:
+//
+//	project.program.getSourceFile("/path/to/file.ts");
+//
+// Using a URI:
+//
+//	project.program.getSourceFile({ uri: "file:///path/to/file.ts" });
 type DocumentIdentifier struct {
 	FileName string              `json:"fileName,omitempty"`
 	URI      lsproto.DocumentUri `json:"uri,omitempty"`
@@ -392,7 +393,7 @@ type UpdateSnapshotResponse struct {
 	// Snapshot is the handle for the newly created snapshot.
 	Snapshot SnapshotID `json:"snapshot"`
 	// Projects is the list of projects in the snapshot.
-	Projects []*ProjectResponse `json:"projects"`
+	Projects []*ProjectResponse `json:"projects" nonnil:"true"`
 	// Changes describes source file differences from the previous snapshot.
 	// Nil for the first snapshot in a session.
 	Changes *SnapshotChanges `json:"changes,omitempty"`
@@ -621,13 +622,13 @@ type ProfileResult struct {
 }
 
 type ConfigFileResponse struct {
-	FileNames         []string                 `json:"fileNames"`
-	Options           *core.CompilerOptions    `json:"options"`
+	FileNames         []string                 `json:"fileNames" nonnil:"true"`
+	Options           *core.CompilerOptions    `json:"options" nonnil:"true"`
 	ProjectReferences []*core.ProjectReference `json:"projectReferences,omitempty"`
 	TypeAcquisition   *core.TypeAcquisition    `json:"typeAcquisition,omitempty"`
 	CompileOnSave     *bool                    `json:"compileOnSave,omitempty"`
 	Raw               any                      `json:"raw,omitempty"`
-	Errors            []*DiagnosticResponse    `json:"errors"`
+	Errors            []*DiagnosticResponse    `json:"errors" nonnil:"true"`
 }
 
 type ReadConfigFileResponse struct {
@@ -641,11 +642,13 @@ type GetDefaultProjectForFileParams struct {
 }
 
 type ProjectResponse struct {
-	Id                ProjectID             `json:"id"`
-	ConfigFileName    string                `json:"configFileName"`
-	ParsedCommandLine *ConfigFileResponse   `json:"parsedCommandLine"`
-	RootFiles         []string              `json:"rootFiles"`
-	CompilerOptions   *core.CompilerOptions `json:"compilerOptions"`
+	Id                ProjectID           `json:"id"`
+	ConfigFileName    string              `json:"configFileName"`
+	ParsedCommandLine *ConfigFileResponse `json:"parsedCommandLine" nonnil:"true"`
+	// Deprecated: Use parsedCommandLine.fileNames.
+	RootFiles []string `json:"rootFiles" nonnil:"true"`
+	// Deprecated: Use parsedCommandLine.options.
+	CompilerOptions *core.CompilerOptions `json:"compilerOptions" nonnil:"true"`
 }
 
 func NewConfigFileResponse(parsedCommandLine *tsoptions.ParsedCommandLine) *ConfigFileResponse {
@@ -753,7 +756,9 @@ type GetSymbolsAtLocationsParams struct {
 }
 
 type SymbolResponse struct {
-	Id               SymbolID     `json:"id"`
+	Id SymbolID `json:"id"`
+	// Project is the project in which the symbol was first observed. It is the
+	// default project for follow-up lookups whose results can vary by project.
 	Project          ProjectID    `json:"project"`
 	Name             string       `json:"name"`
 	Flags            uint32       `json:"flags"`
@@ -792,7 +797,8 @@ type TypeResponse struct {
 	Flags       uint32 `json:"flags"`
 	ObjectFlags uint32 `json:"objectFlags,omitempty"`
 
-	// LiteralType data
+	// Value is literal type data. BigInt literals are encoded as signed decimal
+	// strings because JSON cannot represent bigint; absent values are null.
 	Value any `json:"value"`
 
 	// ObjectType / TypeReference / StringMappingType / IndexType target
@@ -1063,7 +1069,7 @@ type GetReferencedSymbolsForNodeParams struct {
 type ReferencedSymbolEntry struct {
 	Definition NodeHandle      `json:"definition"`
 	Symbol     *SymbolResponse `json:"symbol,omitempty"`
-	References []NodeHandle    `json:"references"`
+	References []NodeHandle    `json:"references" nonnil:"true"`
 }
 
 // GetSignatureUsagesParams are the parameters for the getSignatureUsages method.
@@ -1110,7 +1116,7 @@ type CompletionEntryResponse struct {
 // CompletionInfoResponse wraps a list of completion entries.
 type CompletionInfoResponse struct {
 	IsIncomplete bool                       `json:"isIncomplete"`
-	Entries      []*CompletionEntryResponse `json:"entries"`
+	Entries      []*CompletionEntryResponse `json:"entries" nonnil:"true"`
 }
 
 // GetIntrinsicTypeParams is used for intrinsic type getters (anyType, stringType, etc.).
@@ -1291,8 +1297,8 @@ type SelectedFilesEmitParams struct {
 
 type EmitResponse struct {
 	EmitSkipped  bool                  `json:"emitSkipped"`
-	Diagnostics  []*DiagnosticResponse `json:"diagnostics"`
-	EmittedFiles []string              `json:"emittedFiles"`
+	Diagnostics  []*DiagnosticResponse `json:"diagnostics" nonnil:"true"`
+	EmittedFiles []string              `json:"emittedFiles" nonnil:"true"`
 }
 
 type EmitOutputFile struct {
@@ -1303,8 +1309,8 @@ type EmitOutputFile struct {
 
 type EmitOutputResponse struct {
 	EmitSkipped bool                  `json:"emitSkipped"`
-	Diagnostics []*DiagnosticResponse `json:"diagnostics"`
-	OutputFiles []*EmitOutputFile     `json:"outputFiles"`
+	Diagnostics []*DiagnosticResponse `json:"diagnostics" nonnil:"true"`
+	OutputFiles []*EmitOutputFile     `json:"outputFiles" nonnil:"true"`
 }
 
 // FormatNodeForInsertionParams are the parameters for the formatNodeForInsertion method.
@@ -1386,6 +1392,7 @@ type IndexInfoResponse struct {
 // SourceFileResponse contains the binary-encoded AST data for a source file.
 // The Data field is base64-encoded binary data in the encoder's format.
 type SourceFileResponse struct {
+	// Data is the base64-encoded binary AST data in the encoder's format.
 	Data string `json:"data"`
 }
 
diff --git a/internal/api/session.go b/internal/api/session.go
index 3bb0670ebee..70a602012fb 100644
--- a/internal/api/session.go
+++ b/internal/api/session.go
@@ -1141,6 +1141,7 @@ func (s *Session) handleRelease(ctx context.Context, params *ReleaseParams) (any
 
 // handleGetDefaultProjectForFile returns the default project for a given file,
 // or nil if no project currently contains the file.
+// @gen-proto-nullable
 func (s *Session) handleGetDefaultProjectForFile(ctx context.Context, params *GetDefaultProjectForFileParams) (*ProjectResponse, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -1279,6 +1280,8 @@ func transpileOutput(ctx context.Context, input string, options TranspileOptions
 }
 
 // handleGetSourceFile returns a source file from a project within a snapshot.
+// @gen-proto-result: SourceFileResponse
+// @gen-proto-nullable
 func (s *Session) handleGetSourceFile(ctx context.Context, params *GetSourceFileParams) (any, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -1294,6 +1297,7 @@ func (s *Session) handleGetSourceFile(ctx context.Context, params *GetSourceFile
 }
 
 // handleGetConfigFileNames returns tsconfig file names associated with the project's command line.
+// @gen-proto-nullable
 func (s *Session) handleGetConfigFileNames(ctx context.Context, params *GetProjectDiagnosticsParams) ([]string, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -1318,6 +1322,8 @@ func (s *Session) handleGetConfigFileNames(ctx context.Context, params *GetProje
 }
 
 // handleGetConfigSourceFile returns a tsconfig source file associated with the project's command line.
+// @gen-proto-result: SourceFileResponse
+// @gen-proto-nullable
 func (s *Session) handleGetConfigSourceFile(ctx context.Context, params *GetSourceFileParams) (any, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -1401,6 +1407,7 @@ func (s *Session) handleGetSourceFileNames(ctx context.Context, params *GetSourc
 
 // handleGetSourceFileMetadata returns program-stored metadata for a single source file.
 // The client fetches this lazily per file and caches it.
+// @gen-proto-nullable
 func (s *Session) handleGetSourceFileMetadata(ctx context.Context, params *GetSourceFileParams) (*SourceFileMetadata, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -1428,6 +1435,7 @@ func (s *Session) handleGetSourceFileMetadata(ctx context.Context, params *GetSo
 }
 
 // handleGetSymbolAtPosition returns the symbol at a position in a file.
+// @gen-proto-nullable
 func (s *Session) handleGetSymbolAtPosition(ctx context.Context, params *GetSymbolAtPositionParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -1456,6 +1464,7 @@ func (s *Session) handleGetSymbolAtPosition(ctx context.Context, params *GetSymb
 
 // handleGetSymbolOfSourceFile returns the module symbol for a source file, if any.
 // For non-module (script) files, returns nil.
+// @gen-proto-nullable
 func (s *Session) handleGetSymbolOfSourceFile(ctx context.Context, params *GetSymbolOfSourceFileParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -1527,6 +1536,7 @@ func (s *Session) handleGetSymbolsAtPositions(ctx context.Context, params *GetSy
 }
 
 // handleGetSymbolAtLocation returns the symbol at a node location.
+// @gen-proto-nullable
 func (s *Session) handleGetSymbolAtLocation(ctx context.Context, params *GetSymbolAtLocationParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -1631,6 +1641,7 @@ func (s *Session) handleGetDeclaredTypeOfSymbol(ctx context.Context, params *Get
 }
 
 // handleResolveName resolves a name to a symbol at a given location.
+// @gen-proto-nullable
 func (s *Session) handleResolveName(ctx context.Context, params *ResolveNameParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -1754,6 +1765,7 @@ func (s *Session) handleGetTypeAtLocations(ctx context.Context, params *GetTypeA
 }
 
 // handleGetTypeAtPosition returns the type at a position in a file.
+// @gen-proto-nullable
 func (s *Session) handleGetTypeAtPosition(ctx context.Context, params *GetTypeAtPositionParams) (*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -1809,26 +1821,31 @@ func (s *Session) handleGetTypesAtPositions(ctx context.Context, params *GetType
 	return results, nil
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetParentOfSymbol(_ context.Context, params *GetSymbolPropertyParams) (*SymbolResponse, error) {
 	return s.resolveSymbolPropertyOfSymbol(params, func(sym *ast.Symbol) *ast.Symbol { return sym.Parent })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetMembersOfSymbol(ctx context.Context, params *GetSymbolPropertyParams) ([]*SymbolResponse, error) {
 	return s.resolveSymbolTablePropertyOfSymbol(ctx, params, func(symbol *ast.Symbol) ast.SymbolTable {
 		return symbol.Members
 	})
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetExportsOfSymbol(ctx context.Context, params *GetSymbolPropertyParams) ([]*SymbolResponse, error) {
 	return s.resolveSymbolTablePropertyOfSymbol(ctx, params, func(symbol *ast.Symbol) ast.SymbolTable {
 		return symbol.Exports
 	})
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetExportSymbolOfSymbol(_ context.Context, params *GetSymbolPropertyParams) (*SymbolResponse, error) {
 	return s.resolveSymbolPropertyOfSymbol(params, func(sym *ast.Symbol) *ast.Symbol { return sym.ExportSymbol })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetSymbolOfType(_ context.Context, params *GetTypePropertyParams) (*SymbolResponse, error) {
 	return s.resolveSymbolPropertyOfType(params, (*checker.Type).Symbol)
 }
@@ -1837,30 +1854,37 @@ func (s *Session) handleGetTargetOfType(_ context.Context, params *GetTypeProper
 	return s.resolveTypePropertyOfType(params, (*checker.Type).Target)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetFreshTypeOfType(_ context.Context, params *GetTypePropertyParams) (*TypeResponse, error) {
 	return s.resolveTypePropertyOfType(params, func(t *checker.Type) *checker.Type { return t.AsLiteralType().FreshType() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetRegularTypeOfType(_ context.Context, params *GetTypePropertyParams) (*TypeResponse, error) {
 	return s.resolveTypePropertyOfType(params, func(t *checker.Type) *checker.Type { return t.AsLiteralType().RegularType() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetTypesOfType(_ context.Context, params *GetTypePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfType(params, (*checker.Type).Types)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetTypeParametersOfType(_ context.Context, params *GetTypePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfType(params, func(t *checker.Type) []*checker.Type { return t.AsInterfaceType().TypeParameters() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetOuterTypeParametersOfType(_ context.Context, params *GetTypePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfType(params, func(t *checker.Type) []*checker.Type { return t.AsInterfaceType().OuterTypeParameters() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetLocalTypeParametersOfType(_ context.Context, params *GetTypePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfType(params, func(t *checker.Type) []*checker.Type { return t.AsInterfaceType().LocalTypeParameters() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetAliasTypeArgumentsOfType(_ context.Context, params *GetTypePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfType(params, func(t *checker.Type) []*checker.Type {
 		if t.Alias() == nil {
@@ -1870,6 +1894,7 @@ func (s *Session) handleGetAliasTypeArgumentsOfType(_ context.Context, params *G
 	})
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetAliasSymbolOfType(_ context.Context, params *GetTypePropertyParams) (*SymbolResponse, error) {
 	return s.resolveSymbolPropertyOfType(params, func(t *checker.Type) *ast.Symbol {
 		if t.Alias() == nil {
@@ -1905,18 +1930,22 @@ func (s *Session) handleGetConstraintOfType(_ context.Context, params *GetTypePr
 	return s.resolveTypePropertyOfType(params, func(t *checker.Type) *checker.Type { return t.AsSubstitutionType().SubstConstraint() })
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetTypeParametersOfSignature(_ context.Context, params *GetSignaturePropertyParams) ([]*TypeResponse, error) {
 	return s.resolveTypeArrayPropertyOfSignature(params, (*checker.Signature).TypeParameters)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetParametersOfSignature(_ context.Context, params *GetSignaturePropertyParams) ([]*SymbolResponse, error) {
 	return s.resolveSymbolArrayPropertyOfSignature(params, (*checker.Signature).Parameters)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetThisParameterOfSignature(_ context.Context, params *GetSignaturePropertyParams) (*SymbolResponse, error) {
 	return s.resolveSymbolPropertyOfSignature(params, (*checker.Signature).ThisParameter)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetTargetOfSignature(_ context.Context, params *GetSignaturePropertyParams) (*SignatureResponse, error) {
 	return s.resolveSignaturePropertyOfSignature(params, (*checker.Signature).Target)
 }
@@ -2258,6 +2287,7 @@ func (s *Session) resolveSignaturePropertyOfSignature(params *GetSignatureProper
 }
 
 // handleGetContextualType returns the contextual type for a node.
+// @gen-proto-nullable
 func (s *Session) handleGetContextualType(ctx context.Context, params *GetContextualTypeParams) (*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2419,6 +2449,7 @@ func (s *Session) handleIsTypeAssignableTo(ctx context.Context, params *IsTypeAs
 }
 
 // handleGetShorthandAssignmentValueSymbol returns the value symbol of a shorthand property assignment.
+// @gen-proto-nullable
 func (s *Session) handleGetShorthandAssignmentValueSymbol(ctx context.Context, params *GetTypeAtLocationParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2464,6 +2495,8 @@ func (s *Session) handleGetTypeOfSymbolAtLocation(ctx context.Context, params *G
 }
 
 // handleTypeToTypeNode converts a Type to a TypeNode AST and returns it as binary-encoded data.
+// @gen-proto-result: SourceFileResponse
+// @gen-proto-nullable
 func (s *Session) handleTypeToTypeNode(ctx context.Context, params *TypeToTypeNodeParams) (any, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2502,6 +2535,8 @@ func (s *Session) handleTypeToTypeNode(ctx context.Context, params *TypeToTypeNo
 	}, nil
 }
 
+// @gen-proto-result: SourceFileResponse
+// @gen-proto-nullable
 func (s *Session) handleSignatureToSignatureDeclaration(ctx context.Context, params *SignatureToSignatureDeclarationParams) (any, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2873,6 +2908,7 @@ func (s *Session) handleGetRestTypeOfSignature(ctx context.Context, params *Chec
 }
 
 // handleGetTypePredicateOfSignature returns the type predicate of a signature.
+// @gen-proto-nullable
 func (s *Session) handleGetTypePredicateOfSignature(ctx context.Context, params *CheckerSignatureParams) (*TypePredicateResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2935,6 +2971,7 @@ func (s *Session) handleIsTupleType(ctx context.Context, params *CheckerTypePara
 }
 
 // handleGetBaseTypes returns the base types of an interface/class type.
+// @gen-proto-nullable
 func (s *Session) handleGetBaseTypes(ctx context.Context, params *CheckerTypeParams) ([]*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -2961,6 +2998,7 @@ func (s *Session) handleGetBaseTypes(ctx context.Context, params *CheckerTypePar
 }
 
 // handleGetPropertiesOfType returns the properties of a type.
+// @gen-proto-nullable
 func (s *Session) handleGetPropertiesOfType(ctx context.Context, params *CheckerTypeParams) ([]*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3025,6 +3063,7 @@ func (s *Session) handleGetApparentType(ctx context.Context, params *GetTypeProp
 }
 
 // handleGetIndexInfosOfType returns the index infos of a type.
+// @gen-proto-nullable
 func (s *Session) handleGetIndexInfosOfType(ctx context.Context, params *CheckerTypeParams) ([]*IndexInfoResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3058,6 +3097,7 @@ func (s *Session) handleGetIndexInfosOfType(ctx context.Context, params *Checker
 }
 
 // handleGetConstraintOfTypeParameter returns the constraint of a type parameter.
+// @gen-proto-nullable
 func (s *Session) handleGetConstraintOfTypeParameter(ctx context.Context, params *GetTypePropertyParams) (*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3079,6 +3119,7 @@ func (s *Session) handleGetConstraintOfTypeParameter(ctx context.Context, params
 }
 
 // handleGetDefaultFromTypeParameter returns the default type of a type parameter.
+// @gen-proto-nullable
 func (s *Session) handleGetDefaultFromTypeParameter(ctx context.Context, params *GetTypePropertyParams) (*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3095,6 +3136,7 @@ func (s *Session) handleGetDefaultFromTypeParameter(ctx context.Context, params
 }
 
 // handleGetBaseConstraintOfType returns the base constraint of an instantiable type.
+// @gen-proto-nullable
 func (s *Session) handleGetBaseConstraintOfType(ctx context.Context, params *CheckerTypeParams) (*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3116,6 +3158,7 @@ func (s *Session) handleGetBaseConstraintOfType(ctx context.Context, params *Che
 }
 
 // handleGetPropertyOfType returns a named property symbol of a type.
+// @gen-proto-nullable
 func (s *Session) handleGetPropertyOfType(ctx context.Context, params *GetPropertyOfTypeParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3137,6 +3180,7 @@ func (s *Session) handleGetPropertyOfType(ctx context.Context, params *GetProper
 }
 
 // handleGetConstantValue returns the constant value of an enum member or const enum access.
+// @gen-proto-nullable
 func (s *Session) handleGetConstantValue(ctx context.Context, params *CheckerNodeParams) (any, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3172,6 +3216,7 @@ func (s *Session) handleGetSignatureFromDeclaration(ctx context.Context, params
 }
 
 // handleGetExportSpecifierLocalTargetSymbol returns the local target symbol of an export specifier.
+// @gen-proto-nullable
 func (s *Session) handleGetExportSpecifierLocalTargetSymbol(ctx context.Context, params *CheckerNodeParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3232,6 +3277,7 @@ func (s *Session) handleGetFullyQualifiedName(ctx context.Context, params *Check
 }
 
 // handleGetImmediateAliasedSymbol resolves one level of alias indirection.
+// @gen-proto-nullable
 func (s *Session) handleGetImmediateAliasedSymbol(ctx context.Context, params *CheckerSymbolParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3257,6 +3303,7 @@ func (s *Session) handleGetImmediateAliasedSymbol(ctx context.Context, params *C
 
 // handleGetExportsOfModule returns the resolved exports of a module symbol,
 // including those introduced by `export *` and re-exports.
+// @gen-proto-nullable
 func (s *Session) handleGetExportsOfModule(ctx context.Context, params *CheckerSymbolParams) ([]*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3287,6 +3334,7 @@ func (s *Session) handleGetExportsOfModule(ctx context.Context, params *CheckerS
 }
 
 // handleGetMemberInModuleExports returns an export by name from a module symbol.
+// @gen-proto-nullable
 func (s *Session) handleGetMemberInModuleExports(ctx context.Context, params *GetMemberInModuleExportsParams) (*SymbolResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3311,6 +3359,7 @@ func (s *Session) handleGetMemberInModuleExports(ctx context.Context, params *Ge
 }
 
 // handleGetJSDocTags returns the JSDoc tags of a symbol as structured name/text pairs.
+// @gen-proto-nullable
 func (s *Session) handleGetJSDocTags(ctx context.Context, params *CheckerSymbolParams) ([]*JSDocTagInfo, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3357,6 +3406,7 @@ func (s *Session) handleGetDocumentationComment(ctx context.Context, params *Che
 }
 
 // handleGetTypeArguments returns the type arguments of a type reference.
+// @gen-proto-nullable
 func (s *Session) handleGetTypeArguments(ctx context.Context, params *CheckerTypeParams) ([]*TypeResponse, error) {
 	setup, err := s.setupChecker(ctx, params.Snapshot, params.Project)
 	if err != nil {
@@ -3607,32 +3657,38 @@ func (s *Session) getDiagnostics(ctx context.Context, params *GetDiagnosticsPara
 	return NewDiagnosticResponses(getter(program, ctx, nil)), nil
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetSyntacticDiagnostics(ctx context.Context, params *GetDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	return s.getDiagnostics(ctx, params, (*compiler.Program).GetSyntacticDiagnostics)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetBindDiagnostics(ctx context.Context, params *GetDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	return s.getDiagnostics(ctx, params, (*compiler.Program).GetBindDiagnostics)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetSemanticDiagnostics(ctx context.Context, params *GetDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	return s.getDiagnostics(ctx, params, (*compiler.Program).GetSemanticDiagnostics)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetSuggestionDiagnostics(ctx context.Context, params *GetDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	return s.getDiagnostics(ctx, params, (*compiler.Program).GetSuggestionDiagnostics)
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetDeclarationDiagnostics(ctx context.Context, params *GetDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	return s.getDiagnostics(ctx, params, (*compiler.Program).GetDeclarationDiagnostics)
 }
 
 // handleGetConfigFileParsingDiagnostics returns config file parsing diagnostics.
+// @gen-proto-nullable
 func (s *Session) handleGetConfigFileParsingDiagnostics(ctx context.Context, params *GetProjectDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -3649,6 +3705,7 @@ func (s *Session) handleGetConfigFileParsingDiagnostics(ctx context.Context, par
 }
 
 // handleGetProgramDiagnostics returns program-wide diagnostics, including options diagnostics.
+// @gen-proto-nullable
 func (s *Session) handleGetProgramDiagnostics(ctx context.Context, params *GetProjectDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -3665,6 +3722,7 @@ func (s *Session) handleGetProgramDiagnostics(ctx context.Context, params *GetPr
 }
 
 // handleGetGlobalDiagnostics returns global (non-file-specific) semantic diagnostics.
+// @gen-proto-nullable
 func (s *Session) handleGetGlobalDiagnostics(ctx context.Context, params *GetProjectDiagnosticsParams) ([]*DiagnosticResponse, error) {
 	ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeDiagnostics)
 	sd, err := s.getSnapshotData(params.Snapshot)
@@ -3737,6 +3795,7 @@ func (s *Session) handleGetReferencesToSymbolInFile(ctx context.Context, params
 	return result, nil
 }
 
+// @gen-proto-nullable
 func (s *Session) handleGetSignatureUsages(ctx context.Context, params *GetSignatureUsagesParams) ([]SignatureUsageResponse, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
@@ -3779,6 +3838,7 @@ func (s *Session) handleGetSignatureUsages(ctx context.Context, params *GetSigna
 }
 
 // handleGetCompletionsAtPosition returns completions at a position in a document.
+// @gen-proto-nullable
 func (s *Session) handleGetCompletionsAtPosition(ctx context.Context, params *GetCompletionsAtPositionParams) (*CompletionInfoResponse, error) {
 	if params.IncludeSymbol {
 		ctx = core.WithCheckerLifetime(ctx, core.CheckerLifetimeAPI)
@@ -3835,6 +3895,7 @@ func (s *Session) handleGetCompletionsAtPosition(ctx context.Context, params *Ge
 }
 
 // handleGetReferencedSymbolsForNode returns node handles for all references found at a node.
+// @gen-proto-nullable
 func (s *Session) handleGetReferencedSymbolsForNode(ctx context.Context, params *GetReferencedSymbolsForNodeParams) ([]ReferencedSymbolEntry, error) {
 	sd, err := s.getSnapshotData(params.Snapshot)
 	if err != nil {
diff --git a/internal/core/compileroptions.go b/internal/core/compileroptions.go
index 8f865e62490..051fe5d600f 100644
--- a/internal/core/compileroptions.go
+++ b/internal/core/compileroptions.go
@@ -13,8 +13,7 @@ import (
 //go:generate go tool golang.org/x/tools/cmd/stringer -type=ScriptTarget -trimprefix=ScriptTarget -output=scripttarget_stringer_generated.go
 //go:generate npx dprint fmt modulekind_stringer_generated.go scripttarget_stringer_generated.go
 
-// Keep in sync with the API's compilerOptions.ts
-
+// CompilerOptions contains the compiler options exposed by the API.
 type CompilerOptions struct {
 	_ noCopy
 
@@ -120,45 +119,45 @@ type CompilerOptions struct {
 	MaxNodeModuleJsDepth                      *int                                      `json:"maxNodeModuleJsDepth,omitzero"`
 
 	// Deprecated: Do not use outside of options parsing and validation.
-	AllowSyntheticDefaultImports Tristate `json:"allowSyntheticDefaultImports,omitzero"`
+	AllowSyntheticDefaultImports Tristate `json:"allowSyntheticDefaultImports,omitzero" deprecated:"true"`
 	// Deprecated: Do not use outside of options parsing and validation.
-	AlwaysStrict Tristate `json:"alwaysStrict,omitzero"`
+	AlwaysStrict Tristate `json:"alwaysStrict,omitzero" deprecated:"true"`
 	// Deprecated: Do not use outside of options parsing and validation.
-	BaseUrl string `json:"baseUrl,omitzero"`
+	BaseUrl string `json:"baseUrl,omitzero" deprecated:"true"`
 	// Deprecated: Do not use outside of options parsing and validation.
-	DownlevelIteration Tristate `json:"downlevelIteration,omitzero"`
+	DownlevelIteration Tristate `json:"downlevelIteration,omitzero" deprecated:"true"`
 	// Deprecated: Do not use outside of options parsing and validation.
-	ESModuleInterop Tristate `json:"esModuleInterop,omitzero"`
+	ESModuleInterop Tristate `json:"esModuleInterop,omitzero" deprecated:"true"`
 	// Deprecated: Do not use outside of options parsing and validation.
-	OutFile string `json:"outFile,omitzero"`
+	OutFile string `json:"outFile,omitzero" deprecated:"true"`
 
 	// Internal fields
-	ConfigFilePath      string   `json:"configFilePath,omitzero"`
-	NoDtsResolution     Tristate `json:"noDtsResolution,omitzero"`
-	PathsBasePath       string   `json:"pathsBasePath,omitzero"`
-	Diagnostics         Tristate `json:"diagnostics,omitzero"`
-	ExtendedDiagnostics Tristate `json:"extendedDiagnostics,omitzero"`
-	GenerateCpuProfile  string   `json:"generateCpuProfile,omitzero"`
-	GenerateTrace       string   `json:"generateTrace,omitzero"`
-	ListEmittedFiles    Tristate `json:"listEmittedFiles,omitzero"`
-	ListFiles           Tristate `json:"listFiles,omitzero"`
-	ExplainFiles        Tristate `json:"explainFiles,omitzero"`
-	ListFilesOnly       Tristate `json:"listFilesOnly,omitzero"`
-	NoEmitForJsFiles    Tristate `json:"noEmitForJsFiles,omitzero"`
-	PreserveWatchOutput Tristate `json:"preserveWatchOutput,omitzero"`
-	Pretty              Tristate `json:"pretty,omitzero"`
-	Version             Tristate `json:"version,omitzero"`
-	Watch               Tristate `json:"watch,omitzero"`
-	ShowConfig          Tristate `json:"showConfig,omitzero"`
-	Build               Tristate `json:"build,omitzero"`
-	Help                Tristate `json:"help,omitzero"`
-	All                 Tristate `json:"all,omitzero"`
-	RunExternalCode     Tristate `json:"runExternalCode,omitzero"`
-
-	PprofDir       string   `json:"pprofDir,omitzero"`
-	SingleThreaded Tristate `json:"singleThreaded,omitzero"`
-	Quiet          Tristate `json:"quiet,omitzero"`
-	Checkers       *int     `json:"checkers,omitzero"`
+	ConfigFilePath      string   `json:"configFilePath,omitzero"` // internal, but intentionally exposed via API
+	NoDtsResolution     Tristate `json:"noDtsResolution,omitzero" internal:"true"`
+	PathsBasePath       string   `json:"pathsBasePath,omitzero" internal:"true"`
+	Diagnostics         Tristate `json:"diagnostics,omitzero" internal:"true"`
+	ExtendedDiagnostics Tristate `json:"extendedDiagnostics,omitzero" internal:"true"`
+	GenerateCpuProfile  string   `json:"generateCpuProfile,omitzero" internal:"true"`
+	GenerateTrace       string   `json:"generateTrace,omitzero" internal:"true"`
+	ListEmittedFiles    Tristate `json:"listEmittedFiles,omitzero" internal:"true"`
+	ListFiles           Tristate `json:"listFiles,omitzero" internal:"true"`
+	ExplainFiles        Tristate `json:"explainFiles,omitzero" internal:"true"`
+	ListFilesOnly       Tristate `json:"listFilesOnly,omitzero" internal:"true"`
+	NoEmitForJsFiles    Tristate `json:"noEmitForJsFiles,omitzero" internal:"true"`
+	PreserveWatchOutput Tristate `json:"preserveWatchOutput,omitzero" internal:"true"`
+	Pretty              Tristate `json:"pretty,omitzero" internal:"true"`
+	Version             Tristate `json:"version,omitzero" internal:"true"`
+	Watch               Tristate `json:"watch,omitzero" internal:"true"`
+	ShowConfig          Tristate `json:"showConfig,omitzero" internal:"true"`
+	Build               Tristate `json:"build,omitzero" internal:"true"`
+	Help                Tristate `json:"help,omitzero" internal:"true"`
+	All                 Tristate `json:"all,omitzero" internal:"true"`
+	RunExternalCode     Tristate `json:"runExternalCode,omitzero" internal:"true"`
+
+	PprofDir       string   `json:"pprofDir,omitzero"  internal:"true"`
+	SingleThreaded Tristate `json:"singleThreaded,omitzero" internal:"true"`
+	Quiet          Tristate `json:"quiet,omitzero" internal:"true"`
+	Checkers       *int     `json:"checkers,omitzero" internal:"true"`
 }
 
 // noCopy may be embedded into structs which must not be copied
diff --git a/internal/core/projectreference.go b/internal/core/projectreference.go
index 85bfa82838b..bab89fdd391 100644
--- a/internal/core/projectreference.go
+++ b/internal/core/projectreference.go
@@ -3,9 +3,12 @@ package core
 import "github.com/microsoft/typescript-go/internal/tspath"
 
 type ProjectReference struct {
-	Path         string `json:"path"`
+	// Path is a normalized path on disk.
+	Path string `json:"path"`
+	// OriginalPath is the path as it was originally written.
 	OriginalPath string `json:"originalPath"`
-	Circular     bool   `json:"circular"`
+	// Circular indicates that this reference is intended to form a circularity.
+	Circular bool `json:"circular"`
 }
 
 func ResolveProjectReferencePath(ref *ProjectReference) string {