diff --git a/src/adapters/cursor.ts b/src/adapters/cursor.ts
index a6cb5cbf9d..4089e81ed3 100644
--- a/src/adapters/cursor.ts
+++ b/src/adapters/cursor.ts
@@ -3,8 +3,8 @@ import type { AdapterEvent, OcxProviderConfig } from "../types";
 import type { ProviderAdapter } from "./base";
 import { isTranslatorBudgetExceededError } from "../lib/translator-budget";
 import { cursorExecDeniedMessage, cursorRequestDeclaresFullAccess } from "./cursor/exec-policy";
-import { isCursorBenignCancelError, isCursorInvalidArgumentError, safeCursorErrorMessage } from "./cursor/cursor-errors";
-import { cursorCheckpointModelAffinityId, isCursorExternalWireModel } from "./cursor/discovery";
+import { isCursorBenignCancelError, isCursorInvalidArgumentError, safeCursorErrorMessage, type CursorSizeContext } from "./cursor/cursor-errors";
+import { cursorCheckpointModelAffinityId, inferCursorContextWindow, isCursorExternalWireModel } from "./cursor/discovery";
 import { createCursorKvStore, type CursorKvStore } from "./cursor/kv-store";
 import { mapCursorServerMessage } from "./cursor/message-mapper";
 import {
@@ -25,6 +25,7 @@ import {
   invalidateCursorCheckpoint,
 } from "./cursor/checkpoint-store";
 import { debugProviderDiagnostic } from "../lib/debug";
+import { estimateTokens } from "../lib/token-estimate";
 import { rememberCursorThreadConversation } from "./cursor/thread-continuity";
 import { runCursorTurnWithRetry } from "./cursor/transport-retry";
 import {
@@ -53,16 +54,29 @@ export interface CursorAdapterDeps {
   rekeyContextUsage?: (fromConversationId: string, toConversationId: string) => void;
 }
 
-function safeCursorTransportError(err: unknown): string {
+function safeCursorTransportError(err: unknown, sizeContext?: CursorSizeContext): string {
   if (err instanceof CursorTransportDisabledError) return CURSOR_TRANSPORT_DISABLED_MESSAGE;
   if (err instanceof CursorMissingCredentialError) {
     return "Cursor live transport is enabled, but no Cursor access token is configured. Set provider.apiKey or OPENCODEX_CURSOR_TEST_TOKEN.";
   }
   const message = err instanceof Error ? err.message : typeof err === "string" ? err : undefined;
-  if (message) return safeCursorErrorMessage(message);
+  if (message) return safeCursorErrorMessage(message, sizeContext);
   return "Cursor upstream error: transport failed before completion.";
 }
 
+/**
+ * Size prior for bare resource_exhausted classification (devlog 260): a rough input
+ * estimate over the outgoing text vs the model's context window. Only used to keep
+ * SMALL requests on the 429 class — unknown/large stays on the overflow mapping.
+ */
+function cursorRequestSizeContext(request: { modelId: string; system: string[]; messages: { content: string }[] }): CursorSizeContext {
+  const text = [...request.system, ...request.messages.map(message => message.content)].join("\n");
+  return {
+    estimatedInputTokens: estimateTokens(text, request.modelId),
+    contextWindow: inferCursorContextWindow(request.modelId),
+  };
+}
+
 export function createCursorAdapter(provider: OcxProviderConfig, deps: CursorAdapterDeps = {}): ProviderAdapter {
   return {
     name: "cursor",
@@ -88,6 +102,9 @@ export function createCursorAdapter(provider: OcxProviderConfig, deps: CursorAda
         emit({ type: "error", message: "Cursor turn was aborted before start." });
         return;
       }
+      // Captured after createCursorRequest so the catch block can apply the bare-RE
+      // size prior (devlog 260) even though `request` is scoped inside the try.
+      let requestSizeContext: CursorSizeContext | undefined;
       try {
         const makeTransport = deps.createTransport ?? createLiveCursorTransport;
         const kv = deps.kv ?? createCursorKvStore({}, incoming.translatorBudget);
@@ -110,6 +127,7 @@ export function createCursorAdapter(provider: OcxProviderConfig, deps: CursorAda
         const inheritedCheckpointRef = _parsed._providerContinuation?.cursor?.checkpointRef;
         const previousConversationId = _parsed._cursorConversationId;
         let request = createCursorRequest(_parsed);
+        requestSizeContext = cursorRequestSizeContext(request);
         // The builder may derive a stable provider id from the client thread when Responses state
         // is unavailable. Rekey only existing state; there is nothing to migrate on a fresh turn,
         // and isolated helper/compaction turns must never inherit or donate the parent's usage state.
@@ -292,7 +310,7 @@ export function createCursorAdapter(provider: OcxProviderConfig, deps: CursorAda
           type: "error",
           message: isTranslatorBudgetExceededError(err)
             ? "upstream translation buffer exceeded the safe limit"
-            : safeCursorTransportError(err),
+            : safeCursorTransportError(err, requestSizeContext),
           ...(isTranslatorBudgetExceededError(err)
             ? { status: 502, errorType: "upstream_error", code: "translation_buffer_limit" }
             : {}),
diff --git a/src/adapters/cursor/cursor-errors.ts b/src/adapters/cursor/cursor-errors.ts
index 39f0fc5a8a..33ded8dc7c 100644
--- a/src/adapters/cursor/cursor-errors.ts
+++ b/src/adapters/cursor/cursor-errors.ts
@@ -123,6 +123,30 @@ const QUOTA_RATE_CUES = ["too many requests", "quota", "rate limit", "rate-limit
  */
 const BARE_RE_TAILS = new Set(["error", "", "resource_exhausted", "resource exhausted"]);
 
+/**
+ * Size prior for bare resource_exhausted classification (devlog 260, live probe 210):
+ * a plan-gated model returns the SAME bare RE shape on a ~20-token prompt that a real
+ * payload overflow produces, so the message alone cannot separate "compact and retry"
+ * from "this account cannot use this model". When the caller can supply how large the
+ * request actually was relative to the model's window, a small request keeps the
+ * 429-class mapping; only a plausibly-large one classifies as overflow. Unknown
+ * sizes keep today's overflow mapping so the prior only ever REMOVES false overflows
+ * it can prove.
+ */
+export interface CursorSizeContext {
+  estimatedInputTokens?: number;
+  contextWindow?: number;
+}
+
+const OVERFLOW_MIN_FRACTION = 0.5;
+
+function bareReLooksLikeOverflow(context?: CursorSizeContext): boolean {
+  if (!context) return true;
+  const { estimatedInputTokens, contextWindow } = context;
+  if (estimatedInputTokens === undefined || contextWindow === undefined || contextWindow <= 0) return true;
+  return estimatedInputTokens >= OVERFLOW_MIN_FRACTION * contextWindow;
+}
+
 export function isCursorZeroTokenResourceExhausted(lowerMessage: string): boolean {
   if (!lowerMessage.includes("resource_exhausted") && !lowerMessage.includes("resource exhausted")) return false;
   // Any explicit quota/rate cue wins: this is a real 429.
@@ -172,7 +196,7 @@ export function isCursorRequestTooLargeDetail(lowerMessage: string): boolean {
  * The returned prefix string is recognized by `src/lib/errors.ts` `classifyError` keywords,
  * so bridge-level error mapping produces the right Codex error type (rate_limit, auth, etc.).
  */
-export function classifyCursorError(message: string): string {
+export function classifyCursorError(message: string, sizeContext?: CursorSizeContext): string {
   const lower = message.toLowerCase();
 
   if (isCursorBenignCancelError(message)) return "Cursor stream suspended";
@@ -190,7 +214,11 @@ export function classifyCursorError(message: string): string {
     // A bare resource_exhausted with no quota cue and no size phrase is payload
     // overflow, not rate limiting. Classifying it as 429 makes Codex back off on a
     // failure that only compaction can fix (senpi #1009 / #1036; research unit T01).
-    if (isCursorZeroTokenResourceExhausted(lower)) return "Cursor context limit exceeded";
+    // Refinement (devlog 260): plan-gated models emit the same bare shape on tiny
+    // requests — when the caller proves the request was small, keep the 429 class.
+    if (isCursorZeroTokenResourceExhausted(lower)) {
+      return bareReLooksLikeOverflow(sizeContext) ? "Cursor context limit exceeded" : "Cursor rate limit exceeded";
+    }
     return "Cursor rate limit exceeded";
   }
 
@@ -251,8 +279,8 @@ export function classifyCursorError(message: string): string {
  * Produce a user-facing, secret-safe Cursor error message with an actionable category prefix.
  * Mirrors `safeKiroErrorMessage` / `safeKiroHttpErrorMessage` in kiro-errors.ts.
  */
-export function safeCursorErrorMessage(rawMessage: string): string {
-  const prefix = classifyCursorError(rawMessage);
+export function safeCursorErrorMessage(rawMessage: string, sizeContext?: CursorSizeContext): string {
+  const prefix = classifyCursorError(rawMessage, sizeContext);
   const detail = sanitize(rawMessage)
     .replace(/resource[_ ]exhausted/gi, "resource limit exceeded")
     .slice(0, 500);
diff --git a/tests/cursor-errors.test.ts b/tests/cursor-errors.test.ts
index 3ae5ade2cd..59a7b95399 100644
--- a/tests/cursor-errors.test.ts
+++ b/tests/cursor-errors.test.ts
@@ -136,3 +136,34 @@ describe("isCursorInvalidArgumentError", () => {
     expect(isCursorInvalidArgumentError(new Error("Cursor connection failed"))).toBe(false);
   });
 });
+
+describe("bare resource_exhausted size prior (devlog 260)", () => {
+  const BARE = "Cursor Connect error resource_exhausted: Error";
+
+  test("a provably small request keeps the 429 class (plan-gated model, live probe 210)", () => {
+    expect(classifyCursorError(BARE, { estimatedInputTokens: 20, contextWindow: 200_000 }))
+      .toBe("Cursor rate limit exceeded");
+  });
+
+  test("a plausibly large request still classifies as context overflow", () => {
+    expect(classifyCursorError(BARE, { estimatedInputTokens: 150_000, contextWindow: 200_000 }))
+      .toBe("Cursor context limit exceeded");
+  });
+
+  test("unknown estimate or window keeps today's overflow mapping (prior only removes provable false overflows)", () => {
+    expect(classifyCursorError(BARE)).toBe("Cursor context limit exceeded");
+    expect(classifyCursorError(BARE, {})).toBe("Cursor context limit exceeded");
+    expect(classifyCursorError(BARE, { estimatedInputTokens: 20 })).toBe("Cursor context limit exceeded");
+    expect(classifyCursorError(BARE, { contextWindow: 200_000 })).toBe("Cursor context limit exceeded");
+  });
+
+  test("explicit quota cues stay 429 regardless of size context", () => {
+    expect(classifyCursorError("resource_exhausted: quota exhausted", { estimatedInputTokens: 150_000, contextWindow: 200_000 }))
+      .toBe("Cursor rate limit exceeded");
+  });
+
+  test("explicit size phrases stay resource-limit regardless of size context", () => {
+    expect(classifyCursorError("resource_exhausted: request body exceeds maximum allowed size", { estimatedInputTokens: 20, contextWindow: 200_000 }))
+      .toBe("Cursor resource limit exceeded");
+  });
+});