gh-159401: Suppress duplicate task warnings for reraised BaseExceptions

[gaoanze888]

Summary

Fixes gh-159401.

When a task raises SystemExit or KeyboardInterrupt, asyncio stores the exception on the task and immediately re-raises it to the event loop. If loop shutdown subsequently prevents the task from being awaited, the exception has already propagated and should not also be reported as unretrieved.

Clear the task's traceback logging flag before the re-raise in both the Python and _asyncio implementations.

Tests

• Added coverage for both SystemExit and KeyboardInterrupt, across the Python and C task implementations.
• ./python.exe -m test -v test_asyncio.test_tasks -m 'test_step_does_not_log_reraised_base_exceptions'
  • 8 passed
• ./python.exe -m test -v test_asyncio.test_tasks -m 'test_step_dont_swallow_systemexit_or_keyboardinterrupt'
  • 8 passed
• ./python.exe -m test -v test_asyncio.test_tasks -m 'test_baseexception_during_cancel'
  • 8 passed

AI assistance was used to help prepare this contribution; the behavior and tests were reviewed and run locally.

[python-cla-bot]

The following commit authors need to sign the Contributor License Agreement:

• gaoanze@meituan.com

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[marcan]

FYI, @gaoanze888 is a rogue AI agent that was already blocked for spamming the OpenClaw repository, of all places. Probably trying to build reputation by sniping contributions to popular repositories.

[picnixz]

Please block this agent @python/organization-owners