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

The broad /\b402\b/ regex in ERROR_PATTERNS.billing matched any text
containing '402' (e.g., 'CHE-402', '#402', 'Room 402'), causing
sanitizeUserFacingText() to replace valid agent responses with a
billing error message.

Replace with a context-aware pattern that only matches HTTP 402 error
contexts (e.g., 'status: 402', 'HTTP 402', 'error code 402').

Fixes #13822

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

@@ -27,4 +27,29 @@ describe("isBillingErrorMessage", () => {
     expect(isBillingErrorMessage("invalid api key")).toBe(false);
     expect(isBillingErrorMessage("context length exceeded")).toBe(false);
   });
+  it("does not false-positive on issue IDs or text containing 402", () => {
+    const falsePositives = [
+      "Fixed issue CHE-402 in the latest release",
+      "See ticket #402 for details",
+      "ISSUE-402 has been resolved",
+      "Room 402 is available",
+      "Error code 403 was returned, not 402-related",
+      "The building at 402 Main Street",
+    ];
+    for (const sample of falsePositives) {
+      expect(isBillingErrorMessage(sample)).toBe(false);
+    }
+  });
+  it("still matches real HTTP 402 billing errors", () => {
+    const realErrors = [
+      "HTTP 402 Payment Required",
+      "status: 402",
+      "error code 402",
+      "http 402",
+      "status=402 payment required",
+    ];
+    for (const sample of realErrors) {
+      expect(isBillingErrorMessage(sample)).toBe(true);
+    }
+  });
 });

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

@@ -535,7 +535,7 @@ const ERROR_PATTERNS = {
   overloaded: [/overloaded_error|"type"\s*:\s*"overloaded_error"/i, "overloaded"],
   timeout: ["timeout", "timed out", "deadline exceeded", "context deadline exceeded"],
   billing: [
-    /\b402\b/,
+    /(?:status|code|http|error)\s*[:=]?\s*402\b|^\s*402\s+payment/i,
     "payment required",
     "insufficient credits",
     "credit balance",