fix(model-core): retry OpenAI usage_limit_reached fallbacks

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/model-core/src/model-error-classifier-openai-usage-limit.test.ts

@@ -0,0 +1,18 @@
+import { describe, expect, test } from "bun:test"
+import { shouldRetryError } from "./model-error-classifier"
+
+describe("model-error-classifier OpenAI usage_limit_reached", () => {
+  test("treats OpenAI usage_limit_reached response bodies as retryable provider exhaustion", () => {
+    //#given
+    const error = {
+      name: "AI_APICallError",
+      message: '{"error":{"type":"usage_limit_reached","message":"The usage limit has been reached"}}',
+    }
+
+    //#when
+    const result = shouldRetryError(error)
+
+    //#then
+    expect(result).toBe(true)
+  })
+})

packages/model-core/src/model-error-classifier.test.ts

@@ -172,7 +172,7 @@ describe("model-error-classifier", () => {
     expect(result).toBe(false)
   })
 
-  test("treats usage limit reached message as non-retryable STOP error (no error name)", () => {
+  test("treats provider usage limit reached message as retryable fallback signal", () => {
     //#given
     const error = { message: "usage limit has been reached for your account" }
 
@@ -180,7 +180,7 @@ describe("model-error-classifier", () => {
     const result = shouldRetryError(error)
 
     //#then
-    expect(result).toBe(false)
+    expect(result).toBe(true)
   })
 
   test("treats insufficient credits message as non-retryable STOP error (no error name)", () => {

packages/model-core/src/model-error-classifier.ts

@@ -40,6 +40,8 @@ const NON_RETRYABLE_ERROR_NAMES = new Set([
 const RETRYABLE_MESSAGE_PATTERNS = [
   "rate_limit",
   "rate limit",
+  "usage_limit_reached",
+  "usage limit has been reached",
   "quota",
   "all credentials for model",
   "cooling down",
@@ -92,7 +94,6 @@ const RETRYABLE_MESSAGE_PATTERNS = [
 const STOP_MESSAGE_PATTERNS = [
   "quota will reset after",
   "quota exceeded",
-  "usage limit has been reached",
   "free usage limit",
   "billing limit",
   "billing hard limit",