fix: detect additional context overflow error patterns to prevent leak to user (#20539)

* fix: detect additional context overflow error patterns to prevent leak to user

Fixes #9951

The error 'input length and max_tokens exceed context limit: 170636 +
34048 > 200000' was not caught by isContextOverflowError() and leaked
to users via formatAssistantErrorText()'s invalidRequest fallback.

Add three new patterns to isContextOverflowError():
- 'exceed context limit' (direct match)
- 'exceeds the model\'s maximum context'
- max_tokens/input length + exceed + context (compound match)

These are now rewritten to the friendly context overflow message.

* Overflow: add regression tests and changelog credits

* Update CHANGELOG.md

* Update pi-embedded-helpers.isbillingerrormessage.test.ts

---------

Co-authored-by: echoVic <AkiraVic@outlook.com>
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>

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

@@ -54,6 +54,10 @@ export function isContextOverflowError(errorMessage?: string): boolean {
     lower.includes("model token limit") ||
     (hasRequestSizeExceeds && hasContextWindow) ||
     lower.includes("context overflow:") ||
+    lower.includes("exceed context limit") ||
+    lower.includes("exceeds the model's maximum context") ||
+    (lower.includes("max_tokens") && lower.includes("exceed") && lower.includes("context")) ||
+    (lower.includes("input length") && lower.includes("exceed") && lower.includes("context")) ||
     (lower.includes("413") && lower.includes("too large"))
   );
 }