Keep monitoring side tasks after one returns cleanly

[Sanjays2402]

Closes #1597

_monitor_side_tasks awaited asyncio.wait(..., FIRST_COMPLETED) once and only acted when a completed task had raised, so a side task that returned cleanly silently ended supervision of all the others. That is the normal path rather than an edge case: PeriodicDeferrer.worker() returns immediately when no periodic task is registered, so any app without periodic tasks loses side-task supervision at startup and a later listener/heartbeat failure no longer stops the worker. The monitor now loops over the remaining pending tasks until one fails or all have finished.

This change was prepared with AI assistance; the regression test was run locally and fails without the fix.

Successful PR Checklist:

• Tests
  • (not applicable?)
• Documentation
  • (not applicable?)

PR label(s):

• PR type: breaking 💥 Contains breaking changes
• PR type: feature ⭐️ Contains new features
• PR type: bugfix 🕵️ Contains bug fix
• PR type: miscellaneous 👾 Contains misc changes
• PR type: dependencies 🤖 Contains only dependencies updates
• PR type: documentation 📚 Contains documentation updates

Summary by CodeRabbit

• Bug Fixes

  • Improved background task monitoring so all pending tasks are processed, including tasks that finish at different times.
  • Cancelled tasks no longer interrupt monitoring.
  • Failures continue to trigger worker shutdown and provide error details.

• Tests

  • Added regression coverage for failures occurring after an earlier task completes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3dd77a3e-65eb-45a1-b13e-e6e554312b95

📥 Commits

Reviewing files that changed from the base of the PR and between d9cf91d and c0b9ec0.

📒 Files selected for processing (2)

• procrastinate/worker.py
• tests/unit/test_worker.py

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📝 Walkthrough

Walkthrough

Changes

Side-task supervision

Layer / File(s)	Summary
Iterative side-task monitoring and regression coverage procrastinate/worker.py, tests/unit/test_worker.py	_monitor_side_tasks continues monitoring pending tasks after a task returns cleanly. Cancelled tasks are ignored. Failures still log details and stop the worker. The test verifies a later failure triggers worker shutdown.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: medihack

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the primary change: continued monitoring after a side task returns cleanly.
Linked Issues check	✅ Passed	The implementation and regression test satisfy issue #1597 by preserving supervision and stopping the worker on a later side-task failure.
Out of Scope Changes check	✅ Passed	The changes are limited to side-task monitoring and its regression test, which directly support issue #1597.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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