Document the ~0.3% rotating `trio.TooSlowError`
flake under `--spawn-backend=main_thread_forkserver`
full-suite runs. Root cause: `hard_kill`'s per-sub
1.6s graceful timeout compounding across N subactors
in a cancel cascade, plus cumulative autouse-reaper
teardown overhead.
Covers symptom, observed flaking tests, root-cause
family, ranked mitigations (cap bump -> CPU-count-
aware cap -> `pytest-rerunfailures` -> `hard_kill`
tuning -> targeted profiling), and a verification
protocol.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
(cherry picked from commit 60ce713016)
Gud Boi
d28acfee25