Fix: drain scheduler mocks during fixture teardown

[puddingfjz]

Summary

• add a teardown-only drain mode to MockMailboxWorker
• auto-complete both current and subsequently dispatched work while fixtures unwind
• cover teardown with overlapping queued groups and singles left intentionally incomplete

Why

An assertion can skip the manual complete() calls in a scheduler test. The existing fixture then calls Scheduler::stop(), which waits forever for mock workers that can no longer be completed. A persistent drain mode handles an arbitrary amount of queued teardown work without a fixed retry count.

Review context

#1565 (comment)

Testing

• reproduced the pre-fix hang with a 5-second timeout
• test_scheduler: 27/27 passed
• non-hardware C++ UT: 67/67 passed

[coderabbitai]

📝 Walkthrough

Walkthrough

The test mock worker now supports persistent drain mode. Scheduler fixtures activate this mode before shutdown. A group-scheduler test verifies that teardown completes active and queued dispatches.

Changes

Scheduler teardown draining

Layer / File(s)	Summary
Persistent worker drain mode tests/ut/cpp/hierarchical/test_scheduler.cpp	MockMailboxWorker stores persistent drain state, wakes parked dispatches, and releases dispatches while drain mode is active.
Fixture teardown integration tests/ut/cpp/hierarchical/test_scheduler.cpp	Scheduler fixtures drain their mock workers before shutdown. A group-scheduler test leaves active and queued work for teardown to complete.

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

Poem

A rabbit found dispatches waiting in line,
“Drain mode,” it said, “will make all things fine.”
Workers woke up and queues became clear,
Then schedulers stopped without fear.
Thump-thump, teardown was done!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 15.38% which is insufficient. The required threshold is 80.00%.	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 and concisely describes the scheduler mock teardown drain change.
Description check	✅ Passed	The description explains the teardown drain mode, the failure it fixes, the test coverage, and the observed results.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[ChaoWao]

Addressed the two review Considers (review of #1611 — the inline thread and CI were already clean):

1. drain() semantics — added a comment on the method stating the present-tense contract: it is a persistent teardown mode, so every dispatch including one arriving after the call completes itself, which is what lets Scheduler::stop() always join.

2. TearDownDrainsCurrentAndQueuedDispatches — added a comment stating what the test actually verifies: work is left deliberately in both states (running, and queued-but-not-yet-dispatched), so teardown drains a worker mid-task and one whose dispatch has not happened yet.

Both are comment-only; behavior unchanged. Rebased onto current main; full scheduler suite green locally (39 tests × 30 iterations).

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/ut/cpp/hierarchical/test_scheduler.cpp`:
- Around line 931-933: Update the test teardown around the existing
worker_a/worker_b/worker_c drain calls to also drain the registered SUB workers,
including sub_worker_a and sub_worker_b, before invoking sched.stop(). Preserve
the current drain ordering for the next-level workers while ensuring all SUB
dispatch has completed before scheduler shutdown.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9ccca593-5c67-41df-b5fd-a18f3f478c1b

📥 Commits

Reviewing files that changed from the base of the PR and between b69f453 and 7a52171.

📒 Files selected for processing (1)

• tests/ut/cpp/hierarchical/test_scheduler.cpp