fix(ai): classify Workers AI context window rejections as context overflow (#52128)

packages/ai/src/provider-error.ts

@@ -16,6 +16,8 @@ import {
 const patterns = [
   /prompt is too long/i,
   /input is too long for requested model/i,
+  // Cloudflare Workers AI reports this as HTTP 413.
+  /exceeded this model context window limit/i,
   /exceeds the context window/i,
   /exceeds (?:the )?(?:model'?s )?maximum context length(?: of [\d,]+ tokens?|\s*\([\d,]+\))/i,
   /input token count.*exceeds the maximum/i,

packages/ai/test/provider-error.test.ts

@@ -355,6 +355,17 @@ describe("provider error rawBody classification", () => {
     }
   })
 
+  test("classifies Workers AI context window rejections as context overflow despite HTTP 413", () => {
+    const message =
+      "AiError: Ai: The estimated number of input and maximum output tokens (900047) exceeded this model context window limit (32000). (17851589-f2e6-405d-b67c-5550e52ee1c1)"
+    const reason = classifyProviderFailure({
+      message,
+      status: 413,
+      rawBody: JSON.stringify({ errors: [{ message, code: 5021 }], success: false, result: {}, messages: [] }),
+    })
+    expect(reason._tag === "InvalidRequest" ? reason.classification : reason._tag).toBe("context-overflow")
+  })
+
   test("classifies Google invalid API keys as authentication failures", () => {
     const rawBody = JSON.stringify({
       error: {