[HowieYin]

Summary

Fix requests hanging after a malformed error response.

Connection._handle_response() removes the request from _pending before reading the error payload. If a peer sends "error": ["malformed"], decoding raises before the future receives a result or exception. Disconnect cleanup can no longer find that future, so its caller keeps waiting while the other pending requests receive ConnectionError.

Changes

Keep the future in _pending until its result or exception has been set. If response handling fails, the existing disconnect cleanup can then reject the affected request as well.

Add regressions over real TCP streams for both automatic listening and main_loop(), plus compatibility tests for valid responses, cancellation, duplicate responses, and shutdown.

Testing

Local validation:

• All 8 malformed-response cases fail before the fix and pass afterward. Each verifies that both outstanding requests receive ConnectionError before calling close().
• make check: passed.
• make test: 484 passed, 1 skipped. The skipped test is the optional Gemini integration test.