---
model: claude-opus-4-6
service: claude
session: (ad-hoc, not tracked via conf.toml)
timestamp: 2026-04-06T19:31:25Z
git_ref: 85f9c5d
scope: tests
substantive: true
raw_file: 20260406T193125Z_85f9c5d_prompt_io.raw.md
---

## Prompt

User asked to reproduce the exact `assert not resources.get(ctx_key)`
crash originally seen in piker's `brokerd.kraken` backend via
`open_cached_client('kraken')`. Key constraints from user:

- In piker, kwargs were the **same** (empty) so all callers
  share one `ctx_key = (fid, ())`
- The root issue is `_Cache.locks` being indexed by `fid`
  rather than `ctx_key`, plus the race window between
  `values.pop()` and `resources.pop()` in `_Cache.run_ctx`
  (the acm `__aexit__` has checkpoints in between)
- Mark the test `@pytest.mark.xfail` so it can be committed
  against the unpatched code and later adjusted once the fix
  from `9e49eddd` is applied

User pointed to piker's `open_cached_client('kraken')` usage
as the real-world pattern to model.

## Response summary

Added `test_moc_reentry_during_teardown` which deterministically
reproduces the teardown race:

1. A `cached_client()` acm (no params, like
   `kraken.api.get_client()`) signals via `in_aexit` event
   when its `__aexit__` starts, then sleeps to hold the
   window open
2. `use_and_exit` task enters+exits the cached resource
3. `reenter_during_teardown` waits on `in_aexit` then
   re-enters — landing exactly in the window where
   `values` is popped but `resources` still exists
4. The old `assert not resources.get(ctx_key)` fires
5. `@pytest.mark.xfail(raises=AssertionError)` catches it

Test confirmed: `XFAIL` with the exact traceback at
`_mngrs.py:327`.

## Files changed

- `tests/test_resource_cache.py` — add
  `test_moc_reentry_during_teardown` xfail test fn

## Human edits

None — committed as generated (pending user review).