fix(events): track sync handler futures for mixed event types

[ALDRIN121]

Summary

crewai_event_bus.flush() returns True while a sync handler is still running whenever the event type also has async handlers registered. emit() only registered the sync-handler future with _track_future in the sync-only branch, so the sync half of a mixed event type was invisible to flush() — callers (e.g. crew kickoff finalization, shutdown(wait=True)) could proceed or exit with sync handlers unfinished.

Track the sync future unconditionally and return it only in the sync-only case, matching the shape replay() already uses. The documented return-value contract is unchanged (sync-only → sync future, mixed/async → async future).

Fixes #6745

Validation

• Regression test test_flush_waits_for_sync_handler_when_async_handler_registered: fails on main (flush() returns immediately, sync handler unfinished) and passes with the fix
• Sync-only path guarded by test_flush_waits_for_sync_only_handlers; mixed-case return contract guarded by test_emit_returns_future_for_mixed_handlers
• pytest lib/crewai/tests/events/ lib/crewai/tests/utilities/events/ → 232 passed
• ruff check, ruff format --check, mypy on changed files → clean

[ALDRIN121]

Note for maintainers: this PR was authored with the assistance of Claude Code (AI coding assistant). Per CONTRIBUTING.md, it requires the llm-generated label — external contributors don't have label permissions, so please apply it. Thanks!

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• lib/crewai/tests/events/test_event_bus_flush.py

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📝 Walkthrough

Walkthrough

emit now tracks synchronous handler futures for mixed sync and async events. Tests verify that flush() waits for synchronous handlers and that mixed emissions return the asynchronous future.

Changes

Event bus flush tracking

Layer / File(s)	Summary
Track synchronous futures and validate flush behavior lib/crewai/src/crewai/events/event_bus.py, lib/crewai/tests/events/test_event_bus_flush.py	emit tracks synchronous futures before processing asynchronous handlers. The sync-only path returns the raw synchronous future. Tests cover sync-only completion, mixed-handler completion, flush(), and the mixed-handler return value.

Merge Risk: ⚪ Minimal · up to dba7b

This change makes flush and graceful shutdown wait for synchronous handlers in mixed event types while preserving existing return behavior; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.44% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 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 describes the primary fix: tracking synchronous handler futures for mixed event types.
Description check	✅ Passed	The description explains the mixed sync/async handler bug, the fix, affected behavior, validation, and linked issue #6745.
Linked Issues check	✅ Passed	The changes satisfy issue #6745 by tracking synchronous futures unconditionally, preserving the documented emit() return contract, and adding regression tests for flush() and mixed-handler behavior.
Out of Scope Changes check	✅ Passed	The changes are limited to the event bus fix and focused regression tests. No unrelated code changes are identified.

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Actionable comments posted: 1

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Inline comments:
In `@lib/crewai/tests/events/test_event_bus_flush.py`:
- Around line 66-78: Update the mixed-handler test around slow_sync,
quick_async, and future so the synchronous handler remains blocked until
future.result() completes, then release the handler before calling flush(). Use
synchronization primitives rather than timing assumptions, and assert the
returned future represents the async completion path while preserving the final
flush success check.

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Configuration used: Organization UI

Review profile: CHILL

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Run ID: 5340cb84-0df6-4e9b-b597-60fd25bfed7d

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Reviewing files that changed from the base of the PR and between 4bc5d29 and 11658f2.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/events/event_bus.py
• lib/crewai/tests/events/test_event_bus_flush.py

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