fix(core): resolve cross-runtime fetch and error-handling issues in gaxios, teeny-request, and gcp-metadata - #9519

Summary

Fixes production client library issues across gaxios, teeny-request, and gcp-metadata exposed when running on non-V8 / standard fetch runtimes (such as Bun):

1. teeny-request request timeouts (src/index.ts):

   • requestToFetchOptions previously only passed {timeout: reqOpts.timeout}, a non-standard node-fetch extension ignored by standard fetch / bun:node-fetch.
   • Now also passes signal: AbortSignal.timeout(reqOpts.timeout) when reqOpts.timeout is configured so timeouts are enforced across runtimes.

2. gaxios and teeny-request proxy & mTLS options (gaxios/src/gaxios.ts, teeny-request/src/agents.ts, teeny-request/src/index.ts):

   • Runtimes whose fetch implementation ignores init.agent (such as Bun) previously ignored HTTPS_PROXY/HTTP_PROXY/proxy and mTLS cert/key configuration, or failed to bypass opts.proxy when noProxy matched.
   • gaxios (_defaultAdapter) and teeny-request (requestToFetchOptions) now populate proxy and tls options on the fetch init object alongside agent, and ensure proxy is omitted when noProxy / NO_PROXY excludes the target URL.

3. gaxios non-Error abort reasons and timeout retries (gaxios/src/gaxios.ts, gaxios/src/retry.ts):

   • When AbortController.abort(reason) is called with a non-Error reason (e.g. a string), standard fetch rejects with signal.reason verbatim. Gaxios._request previously fell into new GaxiosError('Unexpected Gaxios Error', ...) without code = 'AbortError' and discarded the reason string. It now preserves the reason in the error message and sets err.code = 'AbortError'.
   • When AbortSignal.timeout triggers, node-fetch throws a generic AbortError (code = undefined) even though opts.signal.reason is DOMException { name: 'TimeoutError' }, causing timeout retry behavior to diverge between node-fetch and native/Bun fetch. Gaxios._request and shouldRetryRequest now inspect signal.reason so timeout retries behave consistently across runtimes.

4. teeny-request Web ReadableStream response body handling (teeny-request/src/index.ts):

   • In stream mode, teenyRequest now converts Web ReadableStream bodies (!(res.body instanceof Readable)) to Node stream.Readable via Readable.fromWeb before attaching stream listeners, while avoiding locking res.body prior to res.json() / res.text() in callback mode and safely handling null response bodies (such as 204 No Content).

5. gcp-metadata empty AggregateError.message (gcp-metadata/src/index.ts):

   • When both primary and secondary metadata requests reject in fastFailMetadataRequest (Promise.any), JavaScriptCore (Bun) constructs an AggregateError with an empty .message (""), causing MetadataLookupWarning in isAvailable() to emit received unexpected error = code = ....
   • fastFailMetadataRequest now normalizes an empty AggregateError.message, and isAvailable() falls back to extracting child error messages when e.message is empty.

Testing

• Added unit tests in core/packages/gcp-metadata/test/index.test.ts, core/packages/teeny-request/test/index.ts, core/packages/gaxios/test/test.getch.ts, and core/packages/gaxios/test/test.retry.ts.