[BUG] Crew.akickoff still does not await async kickoff callbacks (follow-up to #6481)

Description

Crew.akickoff() does not await async before/after kickoff callbacks. An async before-callback's body is not executed when called by synchronous preparation; an async after-callback replaces the result with an unawaited coroutine before post-processing. This report continues #6481, which was closed for inactivity, not because a fix was merged.

Steps to Reproduce

1. Create an otherwise working sequential Crew with a task and its assigned agent.
2. Attach the async callback below to after_kickoff_callbacks.
3. Run result = await crew.akickoff().
4. Check whether the callback executed and the result remains a CrewOutput. Repeat with an async before-callback returning the input dict.

Expected behavior

The native async path awaits awaitable callback results, applies returned inputs/output, and executes each callback once. Synchronous callbacks retain their existing behavior. Offloading blocking synchronous callbacks is outside this report's scope.

Screenshots/Code snippets

called = False

async def after_callback(output):
    global called
    called = True
    return output

# Given an otherwise working Crew:
crew.after_kickoff_callbacks = [after_callback]
result = await crew.akickoff()
assert called

Operating System

Original report: macOS Sonoma. Current verification is source inspection, not a new OS-specific runtime reproduction.

Python Version

Original report: 3.12.

crewAI Version

Originally reported on 1.15.2; source inspected again on 2026-09-19 at main commit 3831e8b6c86f78cb3cde18ebf7be0d197b958f0e.

crewAI Tools Version

Not required: this concerns core Crew kickoff callbacks.

Virtual Environment

Venv (original report).

Evidence

Current main still calls synchronous prepare_kickoff in akickoff and directly assigns result = after_callback(result) without awaiting it: https://github.com/crewAIInc/crewAI/blob/3831e8b6c86f78cb3cde18ebf7be0d197b958f0e/lib/crewai/src/crewai/crew.py#L1275-L1289 . No fresh full-suite test run is claimed here.

Independent historical verification by ErenAta16 on #6500 covered (1) a callback returning None, (2) empty callbacks with inputs=None, and (3) the synchronous control case. The reviewer confirmed the distinct sentinel prevents duplicate callback execution and recommended retaining it: https://github.com/crewAIInc/crewAI/pull/6500#issuecomment-5049732531 . This is historical review evidence, not a maintainer approval of the latest rebased revision.

Possible Solution

Resume review of #6500: await an async preparation entry point and await after-callback results when awaitable. Preserve callback-chain None semantics and exactly-once execution. Validate current hook ordering and regressions against current main before merging.

Additional context

Five related implementation attempts are #6482, #6494, #6500, #6547, and #6697. All five are currently closed and none is recorded as merged. This is not a claim that their technical merits are identical.

Original report: #6481. It was automatically closed for inactivity on August 28. On September 17, #6500 was automatically closed because first-time contributors require an associated OPEN issue. The bot explicitly allows reopening after linking an open issue: https://github.com/crewAIInc/crewAI/pull/6500#issuecomment-5709744042 . This report supplies that active tracking issue while preserving the existing review history.

At inspection, #6500 head 7c202258fde62b7502403c09204f304062fb79e9 is 9 commits behind main; it is not claimed to be fully up to date.

AI disclosure: this issue was prepared with OpenAI Codex. The llm-generated label is requested per CONTRIBUTING.md.

The relevant entry point is lib/crewai/src/crewai/crew.py, especially akickoff and the synchronous prepare_kickoff path. Read the callback handling and historical #6500 discussion first, then verify hook ordering and callback-chain None behavior on current main. Done means async before/after callbacks execute once, awaitable results are applied, CrewOutput remains intact, and synchronous behavior is unchanged.