fix(agents): reduce billing false positives on long text (#25680)

Land PR #25680 from @lairtonlelis.
Retain explicit status/code/http 402 detection for oversized structured payloads.

Co-authored-by: Ailton <lairton@telnyx.com>

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

@@ -69,6 +69,40 @@ describe("isBillingErrorMessage", () => {
       expect(isBillingErrorMessage(sample)).toBe(false);
     }
   });
+  it("does not false-positive on long assistant responses mentioning billing keywords", () => {
+    // Simulate a multi-paragraph assistant response that mentions billing terms
+    const longResponse =
+      "Sure! Here's how to set up billing for your SaaS application.\n\n" +
+      "## Payment Integration\n\n" +
+      "First, you'll need to configure your payment gateway. Most providers offer " +
+      "a dashboard where you can manage credits, view invoices, and upgrade your plan. " +
+      "The billing page typically shows your current balance and payment history.\n\n" +
+      "## Managing Credits\n\n" +
+      "Users can purchase credits through the billing portal. When their credit balance " +
+      "runs low, send them a notification to upgrade their plan or add more credits. " +
+      "You should also handle insufficient balance cases gracefully.\n\n" +
+      "## Subscription Plans\n\n" +
+      "Offer multiple plan tiers with different features. Allow users to upgrade or " +
+      "downgrade their plan at any time. Make sure the billing cycle is clear.\n\n" +
+      "Let me know if you need more details on any of these topics!";
+    expect(longResponse.length).toBeGreaterThan(512);
+    expect(isBillingErrorMessage(longResponse)).toBe(false);
+  });
+  it("still matches explicit 402 markers in long payloads", () => {
+    const longStructuredError =
+      '{"error":{"code":402,"message":"payment required","details":"' + "x".repeat(700) + '"}}';
+    expect(longStructuredError.length).toBeGreaterThan(512);
+    expect(isBillingErrorMessage(longStructuredError)).toBe(true);
+  });
+  it("does not match long numeric text that is not a billing error", () => {
+    const longNonError =
+      "Quarterly report summary: subsystem A returned 402 records after retry. " +
+      "This is an analytics count, not an HTTP/API billing failure. " +
+      "Notes: " +
+      "x".repeat(700);
+    expect(longNonError.length).toBeGreaterThan(512);
+    expect(isBillingErrorMessage(longNonError)).toBe(false);
+  });
   it("still matches real HTTP 402 billing errors", () => {
     const realErrors = [
       "HTTP 402 Payment Required",