fix(backend): stop the async scanner counting awaited calls as blocking

[aryanorastar]

Summary

scan_async_blockers classified every database.* import called inside an async def as a synchronous DB call, without checking whether it was awaited.

await get_async_redis_client() is the correct way to reach the shared async client. The scanner reported it as a blocking helper:

async_helpers_with_blocking: backend/routers/listen/registry.py:49
  | proactive_message_dispatcher | get_async_redis_client:58

Why it needed fixing rather than working around

backend-async-blockers is a blocking pre-push gate, and this scanner has no allowlist, no inline waiver, and no way to record that a finding is wrong. So a correct change becomes unpushable, and the only routes past it are to restructure working code around the linter or to bypass the gate.

Found while routing the proactive dispatcher onto the publisher's shared Redis client — the dispatcher was subscribing to a different server than the publisher writes to, so no message ever arrived.

The change

Calls that are the direct operand of await are skipped. Keyed on AST node identity, not line number — one line can hold an awaited call and a synchronous one, and only the awaited half is safe.

The rule does not widen: an unawaited database.* call inside an async def is still reported, pinned by its own test.

Verification

python3 -m pytest backend/tests/unit/test_scan_async_blockers.py
  -> 27 passed  (25 pre-existing + 2 new)

Guard proven by removing it: with the awaited-call skip deleted, exactly one test fails — the awaited-accessor case. A test that has never failed is not evidence.

Product invariants affected

none

Failure class (fixes)

Failure-Class: none

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.

[aryanorastar]

@Git-on-my-level small one, and it's blocking another PR.

scan_async_blockers counts awaited calls as blocking, so await get_async_redis_client() — the correct way to reach the shared async client — fails backend-async-blockers. No allowlist or inline waiver exists, so the only routes past it are restructuring working code around the linter or bypassing the gate.

Fix skips calls that are the direct operand of await, keyed on AST node identity. Doesn't widen: an unawaited database.* call in an async def is still reported, pinned by its own test.

27 tests pass (25 existing + 2 new). Proven by deleting the guard — exactly one test fails.

Checks green. #11807 can't push until this lands.

[kodjima33]

Confidence 5/5: root cause explained, scoped diff (60 lines, 2 files), CI green, new regression tests (added + removed to prove they catch the bug). Author aryanorastar is a trusted backend contributor per prior history. No abuse signals (no workflow file changes).