fix(a2a): add missing return after 501 in /tasks/metadata endpoint

[mvanhorn]

Summary

Adds a missing return statement after res.status(501).send(...) in the GET /tasks/metadata endpoint.

Without the return, when a non-InMemory task store (e.g., GCSTaskStore) is used, the handler falls through into the try block and attempts to send a second response, crashing the server with ERR_HTTP_HEADERS_SENT.

Changes

• packages/a2a-server/src/http/app.ts: Added return; after the 501 response

Fixes #21729

This contribution was developed with AI assistance (Claude Code).

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical server stability issue by ensuring that the GET /tasks/metadata endpoint correctly terminates execution after sending a 501 'Not Implemented' response. Previously, without the explicit return, the handler would attempt to send a second response, leading to an ERR_HTTP_HEADERS_SENT error and crashing the server, particularly when a task store other than InMemoryTaskStore was configured.

Highlights

• Server Stability Fix: Added a crucial return statement in the GET /tasks/metadata endpoint to prevent server crashes (ERR_HTTP_HEADERS_SENT) that occurred when a non-InMemory task store was in use.

Changelog

• packages/a2a-server/src/http/app.ts
  • Added a return statement after the 501 response to prevent the handler from attempting to send a second response and crashing the server.

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[gemini-code-assist]

Code Review

The pull request introduces a control flow fix in packages/a2a-server/src/http/app.ts. A return statement was added after sending an error response when an unsupported task store is used for listing task metadata, ensuring that the function exits immediately and prevents further execution.

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