feat(fastwire): B0 — per-attempt tier outcomes and per-attempt pricing (#1886)

src/adapters/base.ts

@@ -1,5 +1,6 @@
 import type { AdapterEvent, OcxParsedRequest } from "../types";
 import type { TranslatorBudget } from "../lib/translator-budget";
+import type { AdapterTierMetadata } from "../providers/fastwire";
 
 /** Metadata about the caller's incoming request, for auth-forwarding adapters. */
 export interface IncomingMeta {
@@ -39,6 +40,9 @@ export interface ProviderAdapter {
     incoming: IncomingMeta,
     emit: (event: AdapterEvent) => void,
   ): Promise<void>;
+
+  /** Exact no-field observation for runTurn adapters, which expose no AdapterRequest object. */
+  tierLogForRunTurn?(parsed: OcxParsedRequest): AdapterTierMetadata | undefined;
 }
 
 export interface AdapterRequest {
@@ -67,6 +71,12 @@ export interface AdapterRequest {
           wireField: "reasoning_effort" | "reasoning.effort" | "thinking.type";
           wireValue: string;
         };
+    /**
+     * Exact tier outcome seeded after this adapter serialized the outbound request.
+     * This is a live shared observer: response-phase methods mutate `outcome`, so retain
+     * the reference rather than cloning or snapshotting it.
+     */
+    tierLog?: AdapterTierMetadata;
     usageLog?: {
       inputTokens?: number;
       estimated?: boolean;

src/adapters/openai-chat.ts

@@ -13,6 +13,9 @@ import { peekReasoningForCall } from "../responses/reasoning-replay-cache";
 import { buildNonOpenAIToolCatalogNudgeForTools, shouldInjectNonOpenAIToolCatalogNudge } from "./tool-catalog-nudge";
 import { openRouterProviderPayload, resolveOpenRouterRouting } from "../providers/openrouter-routing";
 import { canSerializeServiceTierForChatModel } from "../providers/service-tier";
+import {
+  createAdapterTierMetadata,
+} from "../providers/fastwire";
 import { openaiChatCompletionsUrl } from "./openai-chat-url";
 import { stripResponsesOnlyEncryptedMarker } from "./responses-tool-schema";
 import {
@@ -1430,6 +1433,13 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
       if (parsed.stream) body.stream_options = { include_usage: true };
 
       const bodyJson = JSON.stringify(body);
+      const actualServiceTier = typeof body.service_tier === "string" ? body.service_tier : null;
+      const tierLog = createAdapterTierMetadata(
+        parsed.options.tierObservation,
+        parsed.options.tierDecision,
+        actualServiceTier === null ? null : "service-tier",
+        actualServiceTier,
+      );
       if (isDebugEnabled()) {
         let host = "upstream";
         try { host = new URL(url).host; } catch { /* keep fallback */ }
@@ -1450,6 +1460,7 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
         headers,
         body: bodyJson,
         ...(reasoningLog ? { reasoningLog } : {}),
+        ...(tierLog ? { tierLog } : {}),
       };
     },
 

src/adapters/openai-responses.ts

@@ -1,6 +1,6 @@
 import { createHash } from "node:crypto";
 import type { IncomingMeta, ProviderAdapter } from "./base";
-import { namespacedToolName, type AdapterEvent, type OcxParsedRequest, type OcxProviderConfig, type OcxUsage } from "../types";
+import { namespacedToolName, type AdapterEvent, type OcxParsedRequest, type OcxProviderConfig, type OcxUsage, type TierDecision } from "../types";
 import { catalogModelSupportsReasoningSummaries } from "../codex/catalog";
 import { COMPACT_PROMPT, decodeCompactionSummary, SUMMARY_PREFIX } from "../responses/compaction";
 import { collectResponsesToolGroups } from "../responses/tool-groups";
@@ -12,6 +12,9 @@ import { modelRecordValue } from "../reasoning-effort";
 import type { TranslatorBudget } from "../lib/translator-budget";
 import { rewriteRoutedCustomToolsForUpstream } from "../responses/custom-tool-compat";
 import { openaiResponsesUrl } from "./openai-responses-url";
+import {
+  createAdapterTierMetadata,
+} from "../providers/fastwire";
 
 // Headers relayed verbatim from the caller in OAuth-passthrough ("forward") mode.
 // Exported so the web-search sidecar reuses the exact same forwarded-auth set for its ChatGPT call.
@@ -764,6 +767,15 @@ function stripPreviousResponseId(body: unknown, strip: boolean): unknown {
   return rest;
 }
 
+/** Apply the settled tier only to a fresh outbound object; `_rawBody` remains caller-owned. */
+function applyTierDecisionToResponsesBody(body: unknown, decision: TierDecision | undefined): unknown {
+  if (!decision || decision.kind === "forward-caller" || !isPlainObject(body)) return body;
+  const next: Record<string, unknown> = { ...body };
+  if (decision.kind === "set") next.service_tier = decision.value;
+  else delete next.service_tier;
+  return next;
+}
+
 /**
  * Drop request parameters a stateless Responses upstream cannot implement, and pin
  * `store` false.
@@ -778,8 +790,8 @@ function stripPreviousResponseId(body: unknown, strip: boolean): unknown {
  * `prompt` is a reference to a server-stored prompt template — the most stateful
  * field in the accepted schema.
  *
- * `service_tier` is deliberately NOT dropped: the server writes it for fast mode
- * (`responses/core.ts`), and silently deleting a configured knob inside an adapter is
+ * `service_tier` is deliberately NOT dropped: the final TierDecision is applied to a
+ * detached outbound body before this sanitizer chain, and silently deleting a configured knob is
  * worse than forwarding a parameter the upstream ignores.
  *
  * MUST run before the composed sanitize chain below: `stripItemIdsWhenUnstored` keys
@@ -1367,6 +1379,9 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
         parsed._rawBody,
         forward || parsed._previousResponseInputExpanded === true,
       );
+      // stripPreviousResponseId() intentionally returns its input on a no-op. Detach before the
+      // tier write so a force-fast/default decision can never mutate parsed._rawBody.
+      outBody = applyTierDecisionToResponsesBody(outBody, parsed.options?.tierDecision);
       const stateless = provider.statelessResponses === true;
       if (stateless) outBody = stripStatefulResponsesParams(outBody);
       // A replay miss can leave a function_call_output whose paired function_call sat
@@ -1414,11 +1429,21 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
         convertedRoutedCustomToolNames = rewritten.names;
       }
       const sanitizedBody = normalizeToolSchemas(stripSparkCompatibility(stripUnsupportedReasoningParams(stripItemIdsWhenUnstored(stripInvalidItemIds(stripUnsupportedHostedTools(sanitizeReasoningInputContent(scrubOcxCompactionItems(outBody), { preserveRawReasoningContent: provider.preserveResponsesReasoningContent === true })))))));
-      const body = JSON.stringify(stripDisabledReasoningSummaries(
+      const finalBody = stripDisabledReasoningSummaries(
         normalizeConfiguredReasoningSummaryDelivery(sanitizedBody, provider, parsed.modelId),
         provider,
         parsed.modelId,
-      ));
+      );
+      const actualServiceTier = isPlainObject(finalBody) && typeof finalBody.service_tier === "string"
+        ? finalBody.service_tier
+        : null;
+      const tierLog = createAdapterTierMetadata(
+        parsed.options?.tierObservation,
+        parsed.options?.tierDecision,
+        actualServiceTier === null ? null : "service-tier",
+        actualServiceTier,
+      );
+      const body = JSON.stringify(finalBody);
       const releaseBodyObservation = translatorBudget.observeExternallyCapped(
         "passthrough_serialization",
         new TextEncoder().encode(body).byteLength,
@@ -1430,6 +1455,7 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
         body,
         releaseBodyObservation,
         ...(convertedRoutedCustomToolNames ? { convertedRoutedCustomToolNames } : {}),
+        ...(tierLog ? { tierLog } : {}),
       };
     },
 

src/adapters/registry.ts

@@ -10,6 +10,7 @@ import { createMimoFreeAdapter } from "./mimo-free";
 import { createOpenAIChatAdapter } from "./openai-chat";
 import { createResponsesPassthroughAdapter } from "./openai-responses";
 import type { OcxProviderConfig } from "../types";
+import { createAdapterTierMetadata } from "../providers/fastwire";
 
 export type AdapterCacheRetention = "none" | "short" | "long";
 
@@ -142,5 +143,33 @@ export function createRegisteredAdapter(
 ): ProviderAdapter {
   const definition = getAdapterDefinition(provider.adapter);
   if (!definition) throw new Error(`Unknown adapter: ${provider.adapter}`);
-  return definition.create(provider, context);
+  const adapter = definition.create(provider, context);
+  const buildRequest = adapter.buildRequest.bind(adapter);
+  adapter.buildRequest = (parsed, incoming) => {
+    const attachTierMetadata = (request: Awaited<ReturnType<ProviderAdapter["buildRequest"]>>) => {
+      // OpenAI-family adapters report the exact emitted field themselves. Other adapters
+      // still report an exact absence at this serialization boundary, which makes a routed
+      // Fast downgrade observable without asking core to infer an outbound body shape.
+      request.tierLog ??= createAdapterTierMetadata(
+        parsed.options.tierObservation,
+        parsed.options.tierDecision,
+        null,
+        null,
+      );
+      return request;
+    };
+    const request = buildRequest(parsed, incoming);
+    return request instanceof Promise
+      ? request.then(attachTierMetadata)
+      : attachTierMetadata(request);
+  };
+  if (adapter.runTurn && !adapter.tierLogForRunTurn) {
+    adapter.tierLogForRunTurn = parsed => createAdapterTierMetadata(
+      parsed.options.tierObservation,
+      parsed.options.tierDecision,
+      null,
+      null,
+    );
+  }
+  return adapter;
 }

src/codex/catalog/provider-fetch.ts

@@ -33,10 +33,10 @@ import { CODEX_REASONING_LEVELS, codexEffortRank, configuredReasoningEfforts, mo
 import { getModelMetadata, getModelMetadataCaseInsensitive, listModelMetadata, resolveMetadataProvider } from "../../generated/model-metadata";
 import { enrichProviderFromRegistry, shouldCaseFoldMetadataModelId } from "../../providers/derive";
 import {
-  captureServiceTierAdapterAuthority,
+  captureFastPolicyAuthority,
   serviceTierSupportForModel,
-  type CapturedServiceTierAdapterAuthority,
 } from "../../providers/service-tier";
+import type { FastPolicyAuthority } from "../../providers/fastwire";
 import { effectiveGoogleMode, getProviderRegistryEntry, providerMatchesRegistryTransport } from "../../providers/registry";
 import { parseAntigravityAvailableModels, registerAntigravityDiscoveredWireModels } from "../../providers/antigravity-models";
 import { applyProviderContextCap, providerContextCap } from "../../providers/context-cap";
@@ -155,7 +155,7 @@ interface CapturedProviderGather {
   readonly discovery: ResolvedProviderModelDiscovery;
   readonly policy: CatalogProviderDiscoveryPolicySnapshot;
   readonly request: CapturedModelsRequest;
-  readonly serviceTierAdapterAuthority: CapturedServiceTierAdapterAuthority;
+  readonly fastPolicyAuthority: FastPolicyAuthority;
   readonly observedAuth?: ModelsAuthResolution;
   /**
    * Configured model ids this provider must keep even when live discovery omits
@@ -408,12 +408,12 @@ function captureProviderGather(
   const enriched = detachedClone(withCanonicalOpenAiForwardAuthDefault(name, configured));
   enrichProviderFromRegistry(name, enriched);
   const registryTransportMatch = providerMatchesRegistryTransport(name, enriched);
-  const serviceTierAdapterAuthority = captureServiceTierAdapterAuthority(
+  const provider = recursivelyFreeze(enriched);
+  const fastPolicyAuthority = captureFastPolicyAuthority(
     name,
-    enriched,
+    provider,
     registryTransportMatch,
   );
-  const provider = recursivelyFreeze(enriched);
   const observedAuth = authResolver.kind === "observed"
     && provider.authMode !== "forward"
     && provider.liveModels !== false
@@ -449,7 +449,7 @@ function captureProviderGather(
     discovery,
     policy,
     request,
-    serviceTierAdapterAuthority,
+    fastPolicyAuthority,
     ...(observedAuth ? { observedAuth: Object.freeze({ ...observedAuth }) } : {}),
     ...(retainConfiguredModelIds && retainConfiguredModelIds.size > 0
       ? { retainConfiguredModelIds }
@@ -518,7 +518,7 @@ function captureGatherFlight(
         // It is the one member of a provider row that is legitimately a function,
         // so it is dropped here rather than allowed to break every encode.
         provider: omitProviderTransportExecutor(provider.provider),
-        serviceTierAdapterAuthority: provider.serviceTierAdapterAuthority,
+        fastPolicyAuthority: provider.fastPolicyAuthority,
         // Combo retention is capture-time state, not a provider-row field. Two
         // gathers that share providers but differ in combo targets must not join.
         retainConfiguredModelIds: [...(provider.retainConfiguredModelIds ?? [])].sort(),