fix: avoid context-window-too-small misclassification (#1266, thanks @humanwritten)

Co-authored-by: humanwritten <humanwritten@users.noreply.github.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ Docs: https://docs.clawd.bot
 - TUI: keep thinking blocks ordered before content during streaming and isolate per-run assembly. (#1202) — thanks @aaronveklabs.
 - CLI: avoid duplicating --profile/--dev flags when formatting commands.
 - Auth: dedupe codex-cli profiles when tokens match custom openai-codex entries. (#1264) — thanks @odrobnik.
+- Agents: avoid misclassifying context-window-too-small errors as context overflow. (#1266) — thanks @humanwritten.
 
 ## 2026.1.19-3
 

src/agents/pi-embedded-helpers.islikelycontextoverflowerror.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+import { isLikelyContextOverflowError } from "./pi-embedded-helpers.js";
+import { DEFAULT_AGENTS_FILENAME } from "./workspace.js";
+
+const _makeFile = (overrides: Partial<WorkspaceBootstrapFile>): WorkspaceBootstrapFile => ({
+  name: DEFAULT_AGENTS_FILENAME,
+  path: "/tmp/AGENTS.md",
+  content: "",
+  missing: false,
+  ...overrides,
+});
+
+describe("isLikelyContextOverflowError", () => {
+  it("matches context overflow hints", () => {
+    const samples = [
+      "Model context window is 128k tokens, you requested 256k tokens",
+      "Context window exceeded: requested 12000 tokens",
+      "Prompt too large for this model",
+    ];
+    for (const sample of samples) {
+      expect(isLikelyContextOverflowError(sample)).toBe(true);
+    }
+  });
+
+  it("excludes context window too small errors", () => {
+    const samples = [
+      "Model context window too small (minimum is 128k tokens)",
+      "Context window too small: minimum is 1000 tokens",
+    ];
+    for (const sample of samples) {
+      expect(isLikelyContextOverflowError(sample)).toBe(false);
+    }
+  });
+});

src/agents/pi-embedded-helpers.ts

@@ -19,6 +19,7 @@ export {
   isCloudCodeAssistFormatError,
   isCompactionFailureError,
   isContextOverflowError,
+  isLikelyContextOverflowError,
   isFailoverAssistantError,
   isFailoverErrorMessage,
   isImageDimensionErrorMessage,

src/agents/pi-embedded-helpers/errors.ts

@@ -18,6 +18,17 @@ export function isContextOverflowError(errorMessage?: string): boolean {
   );
 }
 
+const CONTEXT_WINDOW_TOO_SMALL_RE = /context window.*(too small|minimum is)/i;
+const CONTEXT_OVERFLOW_HINT_RE =
+  /context.*overflow|context window.*(too (?:large|long)|exceed|over|limit|max(?:imum)?|requested|sent|tokens)|(?:prompt|request|input).*(too (?:large|long)|exceed|over|limit|max(?:imum)?)/i;
+
+export function isLikelyContextOverflowError(errorMessage?: string): boolean {
+  if (!errorMessage) return false;
+  if (CONTEXT_WINDOW_TOO_SMALL_RE.test(errorMessage)) return false;
+  if (isContextOverflowError(errorMessage)) return true;
+  return CONTEXT_OVERFLOW_HINT_RE.test(errorMessage);
+}
+
 export function isCompactionFailureError(errorMessage?: string): boolean {
   if (!errorMessage) return false;
   if (!isContextOverflowError(errorMessage)) return false;

src/auto-reply/reply/agent-runner-execution.ts

@@ -9,6 +9,7 @@ import { runEmbeddedPiAgent } from "../../agents/pi-embedded.js";
 import {
   isCompactionFailureError,
   isContextOverflowError,
+  isLikelyContextOverflowError,
   sanitizeUserFacingText,
 } from "../../agents/pi-embedded-helpers.js";
 import {
@@ -419,10 +420,7 @@ export async function runAgentTurnWithFallback(params: {
       break;
     } catch (err) {
       const message = err instanceof Error ? err.message : String(err);
-      const isContextOverflow =
-        isContextOverflowError(message) ||
-        (/context.*overflow|too large|context window/i.test(message) &&
-          !/too small|minimum is/i.test(message));
+      const isContextOverflow = isLikelyContextOverflowError(message);
       const isCompactionFailure = isCompactionFailureError(message);
       const isSessionCorruption = /function call turn comes immediately after/i.test(message);
       const isRoleOrderingError = /incorrect role information|roles must alternate/i.test(message);