[bgeng777]

Fixes #40774.

When a data channel closes after a read failure, input_elements hides the saved exception. Chain it as the cause of Channel closed prematurely; suppress the unrelated queue.Empty context when no cause exists.

Tests cover reader failure, premature EOF, normal completion and cancellation. All 9 data-plane tests pass; the two diagnostic regressions fail without the fix. Ruff and YAPF pass.

AI assistance: OpenAI Codex.

[github-actions]

📋 Review Summary

This PR preserves the underlying data-plane exception as the explicit __cause__ when _GrpcDataChannel.input_elements raises RuntimeError('Channel closed prematurely.'), improving error diagnostics while suppressing the noisy queue.Empty context when no exception was recorded. The implementation is minimal, backwards-compatible, and well-covered by new unit tests.

🔍 General Feedback

• Chaining from self._exception cleanly addresses the race/ordering between self._closed and self._exception in _read_inputs without altering existing exception types or abort semantics.
• Consider mocking or shortening the queue poll timeout in the new unit tests, as 3 of the 4 added tests each wait on the hardcoded received.get(timeout=1) call (~3 seconds total).

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[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.90%. Comparing base (2213e54) to head (2e5ef38).
⚠️ Report is 23 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #40775       +/-   ##
===========================================
+ Coverage        0   79.90%   +79.90%     
===========================================
  Files           0      493      +493     
  Lines           0    83473    +83473     
===========================================
+ Hits            0    66696    +66696     
- Misses          0    16777    +16777     

Flag	Coverage Δ
python	79.90% <100.00%> (?)

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[jrmccluskey]

LGTM, thanks!