test(conftest): reap leaked libtmux_test* sockets after session

[tony]

Summary

Add a session-scoped autouse fixture in tests/conftest.py that reaps leaked libtmux_test* tmux daemons and socket files under /tmp/tmux-<uid>/ after every test run.

Upstream libtmux's pytest plugin (tmux-python/libtmux#660) does not reliably kill the per-test tmux daemons or unlink the socket files on teardown. Over repeated runs, /tmp/tmux-<uid>/ accumulates stale entries indefinitely — 10,693 were observed on a dev machine before this fixture ran.

Root-cause fix filed upstream at tmux-python/libtmux#661. Once that lands and the downstream libtmux dependency is bumped, this local mitigation can be reverted — the upstream fixture finalizers will do the reaping at the source.

Until then this provides a local safety net so CI and dev machines stay clean regardless of which libtmux version the working checkout pulls in.

Safe properties:

• Prefix match on libtmux_test* only — never touches the developer's real default socket or any non-test socket.
• Scope session + autouse — runs exactly once after every pytest invocation without opt-in.
• Idempotent under xdist (each worker is its own session; kill() and unlink(missing_ok=True) are safe on already-gone sockets).
• POSIX-guarded via hasattr(os, 'geteuid'); errors suppressed because any failure is a race with a concurrent worker or a vanished socket — neither actionable.

Test plan

• uv run ruff check . --fix --show-fixes
• uv run ruff format .
• uv run mypy
• uv run py.test --reruns 0 -vvv (363 passed)
• just build-docs

End-to-end verification: ls /tmp/tmux-\$(id -u) | grep -c libtmux_test dropped 10693 → 0 after a single uv run pytest on this branch.

Companion PRs

Part of a batch of post-0.1.0a2 smoke-test fixes. Each PR is independent and can land in any order:

• fix(wait_for_tools): unblock event loop via asyncio.to_thread #21 — event-loop block in channel waits (closes wait_for_channel and signal_channel block the FastMCP event loop (sync subprocess.run) #18)
• fix(_utils): scope is_caller annotation to caller's socket #22 — is_caller socket-blind false positive (closes is_caller annotation gives false positives across tmux sockets #19)
• test(conftest): reap leaked libtmux_test* sockets after session #23 — pytest leaks libtmux_test* sockets (this PR, closes list_servers exposes dozens of leaked libtmux_test* tmux daemons after test runs #20)
• Upstream: tmux-python/libtmux#661 — root-cause fix in the libtmux pytest plugin

Closes #20

[codecov-commenter]

Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.89%. Comparing base (58af71f) to head (5e2f949).

Files with missing lines	Patch %	Lines
tests/conftest.py	73.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #23      +/-   ##
==========================================
- Coverage   87.01%   86.89%   -0.12%     
==========================================
  Files          38       38              
  Lines        1710     1725      +15     
  Branches      201      205       +4     
==========================================
+ Hits         1488     1499      +11     
- Misses        164      166       +2     
- Partials       58       60       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.