fix: close the platform events websocket iterator on shutdown

[vdusek]

Since v4.0.0, an Actor logs RuntimeError: aclose(): asynchronous generator is already running right after Actor.exit(). Cosmetic - the exit code stays 0 and no data is lost - but it shows up in every run and looks like a failure.

ApifyEventManager._process_platform_messages iterates websockets connect(...) with async for. That iterator is an async generator, and neither break nor cancelling the task closes it, so the garbage collector does - during asyncio.run teardown, where the aclose() it schedules lands after _cancel_all_tasks took its task snapshot and is never awaited. loop.shutdown_asyncgens() then calls aclose() on a generator that is still running. Up to v3.4.1 the code used async with connect(...), which unwound synchronously on cancellation.

contextlib.aclosing closes the iterator on every exit path - break, exception and cancellation alike. The rest of the diff is the loop body re-indenting, a unit test that asserts the iterator is closed, and an E2E test that asserts the error is absent from a run log.

Reported on Discord.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.90%. Comparing base (90d1725) to head (2d231f2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/apify/events/_apify_event_manager.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1077      +/-   ##
==========================================
- Coverage   91.92%   91.90%   -0.03%     
==========================================
  Files          51       51              
  Lines        3232     3235       +3     
==========================================
+ Hits         2971     2973       +2     
- Misses        261      262       +1     

Flag	Coverage Δ
e2e	35.30% <5.55%> (-0.04%)	⬇️
integration	57.03% <5.55%> (-0.09%)	⬇️
unit	83.27% <94.44%> (+0.01%)	⬆️

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[Mantisus]

LGTM