Default `timeout` from `int = 3` → `int|None = None`;
when unset, pick a backend-aware value. Fork-based
backends (`main_thread_forkserver`) need real headroom
bc actor spawn + IPC ctx-exit + msg-validation error
path is much heavier than under `trio` backend —
especially under cross-pytest-stream contention (#451).
Defaults:
- `main_thread_forkserver` → 30s
- everything else → 3s (unchanged)
Empirical flake history that motivated 30s as the floor
on fork backends (all from `test_basic_payload_spec`):
- 3s → all-valid variant flaked w/ `TooSlowError`
- 8s → `invalid-return` variant flaked w/ `Cancelled`
(surfaced instead of `MsgTypeError` bc the
outer `fail_after` fired mid-error-path)
- 15s → flaked under cross-pytest-stream contention
30s gives plenty of headroom while still failing-loud
on a genuine hang. Callers can opt out by passing an
explicit `timeout=` kw.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi
060f7d24c4