fix(agents): narrow billing error 402 regex to avoid false positives on issue IDs (#13827)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: b0501bbab7
Co-authored-by: 0xRaini <190923101+0xRaini@users.noreply.github.com>
Co-authored-by: sebslight <19554889+sebslight@users.noreply.github.com>
Reviewed-by: @sebslight

src/agents/live-auth-keys.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+import { isAnthropicBillingError } from "./live-auth-keys.js";
+
+describe("isAnthropicBillingError", () => {
+  it("does not false-positive on plain 'a 402' prose", () => {
+    const samples = [
+      "Use a 402 stainless bolt",
+      "Book a 402 room",
+      "There is a 402 near me",
+      "The building at 402 Main Street",
+    ];
+
+    for (const sample of samples) {
+      expect(isAnthropicBillingError(sample)).toBe(false);
+    }
+  });
+
+  it("matches real 402 billing payload contexts including JSON keys", () => {
+    const samples = [
+      "HTTP 402 Payment Required",
+      "status: 402",
+      "error code 402",
+      '{"status":402,"type":"error"}',
+      '{"code":402,"message":"payment required"}',
+      '{"error":{"code":402,"message":"billing hard limit reached"}}',
+      "got a 402 from the API",
+      "returned 402",
+      "received a 402 response",
+    ];
+
+    for (const sample of samples) {
+      expect(isAnthropicBillingError(sample)).toBe(true);
+    }
+  });
+});