fix(flow): preserve parallel branches feeding OR listeners

[ShyamRV]

Summary

• stop treating producers referenced by an or_() listener as a first-wins race
• allow independently triggered fan-out branches to run to completion
• add a regression test proving both branches complete while the OR join fires once

Closes #7183

Test plan

• Focused OR-listener regression tests (2 passed)

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Reviewing files that changed from the base of the PR and between 49976be and 660831b.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/flow/runtime/__init__.py
• lib/crewai/tests/test_flow.py

🚧 Files skipped from review as they are similar to previous changes (2)

• lib/crewai/tests/test_flow.py
• lib/crewai/src/crewai/flow/runtime/init.py

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📝 Walkthrough

Walkthrough

The flow runtime removes first-wins racing for OR listeners. It executes all triggered listeners concurrently and propagates listener exceptions. Tests verify parallel branch completion, single OR join execution, and sibling completion after failure.

Changes

OR listener execution

Layer / File(s)	Summary
Remove OR listener racing lib/crewai/src/crewai/flow/runtime/__init__.py	The runtime removes OR alternative extraction, racing-group caching, and first-wins listener execution.
Parallel listener dispatch and regression coverage lib/crewai/src/crewai/flow/runtime/__init__.py, lib/crewai/tests/test_flow.py	Listener dispatch gathers all triggered listeners and re-raises exceptions. Tests verify that both OR branches complete, the join runs once, and an independently triggered sibling completes after another listener fails.

Merge Risk: ⚪ Minimal · up to 66083

This change updates OR-listener branch handling and adds regression coverage; no actionable merge-blocking risk remains based on the supplied evidence.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the flow bug and the required preservation of parallel branches feeding OR listeners.
Description check	✅ Passed	The description provides the linked issue, solution summary, and focused verification results. It omits the template's explicit Additional context section and does not list the general quality-check i…
Linked Issues check	✅ Passed	The implementation removes first-wins producer cancellation, runs triggered listeners concurrently, preserves OR-listener deduplication, and adds regression tests for branch completion and single OR e…
Out of Scope Changes check	✅ Passed	The runtime changes and regression tests directly address the OR-join cancellation bug. No unrelated code changes are indicated.

Full details: Description check

Explanation

The description provides the linked issue, solution summary, and focused verification results. It omits the template's explicit Additional context section and does not list the general quality-check item, but the required information is mostly present.

Full details: Linked Issues check

Explanation

The implementation removes first-wins producer cancellation, runs triggered listeners concurrently, preserves OR-listener deduplication, and adds regression tests for branch completion and single OR execution. These changes satisfy the coding objectives in [#7183].

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[ShyamRV]

Looks good

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Actionable comments posted: 1

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Inline comments:
In `@lib/crewai/src/crewai/flow/runtime/__init__.py`:
- Line 3093: Update the listener-task gathering in the kickoff flow to await all
tasks with return_exceptions=True, then re-raise the first listener exception
after every sibling has finished; preserve successful listener results and
existing failure propagation semantics. Add a regression test covering a
fast-failing listener alongside a slower listener that must complete its state
update or tool call.

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Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: c0a342a3-466a-458c-abcb-464c1749c2e3

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Reviewing files that changed from the base of the PR and between 381fef7 and 49976be.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/flow/runtime/__init__.py
• lib/crewai/tests/test_flow.py

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[VANDRANKI]

Community review, does not clear the merge gate.

Read the whole diff. This removes the "racing groups" mechanism (_build_racing_groups, _get_racing_group_for_listeners, _execute_racing_listeners, _racing_groups_cache, _or_alternative_events) from lib/crewai/src/crewai/flow/runtime/init.py entirely, replacing the branch in _execute_listeners with a plain asyncio.gather(*tasks, return_exceptions=True) plus a loop that re-raises the first exception after all tasks finish.

The bug this fixes, as I understand it from the new tests: the old code treated any two listeners that exclusively co-fed the same or_() listener as "racing alternatives" and cancelled whichever one lost the race. That's correct for genuine either/or alternatives, but wrong for a parallel fan-out where two independent branches (e.g. fast_branch and slow_branch, both @listen(begin)) both legitimately need to run to completion, and just happen to both also feed one @listen(or_(fast_branch, slow_branch)) join. The old code would cancel the slower branch once the join fired, silently losing its side effects. test_or_listener_does_not_cancel_parallel_fanout_branches demonstrates exactly this and asserts both branches complete.

I checked for regressions from the removal two ways:

1. Grepped the PR's head branch for any remaining reference to the five removed names -- none found, so nothing is left calling into deleted code.
2. Checked whether "OR listener fires exactly once" still holds without the removed cancellation logic. It does: that guarantee comes from a separate, still-present mechanism, _fired_or_listeners (checked at line ~3136, guarding against re-firing), which this PR does not touch. So removing the racing/cancellation code does not reopen the double-fire problem the mechanism might have also been protecting against.

The second new test (test_parallel_listener_failure_waits_for_siblings) confirms return_exceptions=True plus manual re-raise means a failing listener doesn't cancel siblings either, it still lets them finish before the exception propagates.

I traced this end to end and I'm comfortable approving.