fix(_utils): scope is_caller annotation to caller's socket

[tony]

Summary

Pane serializers (_serialize_pane, snapshot_pane, search_panes) compared pane.pane_id == TMUX_PANE without consulting the tmux socket. A caller on socket A pane %0 was therefore flagged is_caller=True for any %0 on any other server — a false positive that polluted every read-path tool returning PaneInfo / PaneSnapshot / PaneContentMatch.

The 0.1.0a2 caller-identity-scoping work already shipped _caller_is_on_server (realpath comparison + macOS TMUX_TMPDIR basename fallback), but wired it into the self-kill guard only. This PR extends it to the informational annotation via a new _compute_is_caller(pane) helper in _utils.py, and migrates all three call sites. The now-dead _get_caller_pane_id helper and its two unit tests are removed.

Test plan

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

New regression test test_serialize_pane_is_caller_false_across_sockets spawns two libtmux servers via the TestServer fixture, points the caller at server A, and asserts pane %0 on server B (same pane_id, different socket) is flagged False. Sanity: pane %0 on server A is still True. The existing test_serialize_pane_is_caller parametrization continues to pass — the no-TMUX-set conservative branch is preserved for consistency with _caller_is_on_server.

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 (this PR, 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 (closes list_servers exposes dozens of leaked libtmux_test* tmux daemons after test runs #20)

Closes #19

[codecov-commenter]

Codecov Report

❌ Patch coverage is 71.42857% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.62%. Comparing base (8e2e0c3) to head (02fef68).

Files with missing lines	Patch %	Lines
src/libtmux_mcp/_utils.py	71.42%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
- Coverage   86.78%   86.62%   -0.17%     
==========================================
  Files          38       38              
  Lines        1710     1719       +9     
  Branches      201      204       +3     
==========================================
+ Hits         1484     1489       +5     
- Misses        167      170       +3     
- Partials       59       60       +1     

☔ 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.

[tony]

Code review

No issues found. Checked for bugs and AGENTS.md compliance (repo has AGENTS.md, no CLAUDE.md).

Scope:

• AGENTS.md (namespace imports, test patterns).
• Shallow bug scan on the diff — tri-state semantics of _compute_is_caller verified; 12 call sites of _serialize_pane accounted for; three migrated sites (_serialize_pane, snapshot_pane, search_panes) confirmed as complete.
• Git blame / history — matches prior scoping work on the self-kill guard.
• Prior PR review comments — no applicable guidance.
• Code comments — _caller_is_on_server's conservative-True semantics at src/libtmux_mcp/_utils.py are inherited rather than tightened; this is intentional for parity with the self-protection gate, though reviewers may wish to note it as a trade-off (basename fallback and TMUX_PANE-only branches keep conservative-True behavior for the annotation).

🤖 Generated with Claude Code

_{- If this code review was useful, please react with 👍. Otherwise, react with 👎.}

[tony]

Code review

Re-reviewed after force-push to 02fef68 (squashed fixups for the three concerns noted in the prior review).

No blocking issues found. Checked for bugs and AGENTS.md compliance.

Scope of the re-review:

• Strict comparator. The new _caller_is_strictly_on_server is a proper subset of _caller_is_on_server — keeps the realpath positive branch, drops the basename fallback, TMUX_PANE-only-True, and unresolvable-target-True branches that the prior review flagged as unsafe for an informational annotation.
• Fixture flips. matching_pane_id_no_tmux_env in tests/test_utils.py and caller_pane_no_tmux_env in tests/test_pane_tools.py correctly flip expected_is_caller True → False with explanatory fixture comments.
• Regression coverage. New test_serialize_pane_is_caller_requires_tmux_env_not_just_pane exercises the TMUX_PANE-without-TMUX path that was previously uncovered.
• Model docstrings. All three is_caller Field descriptions are now identical and document the tri-state semantics.

The prior review's concern about conservative-True semantics leaking into the annotation is resolved.

🤖 Generated with Claude Code

_{- If this code review was useful, please react with 👍. Otherwise, react with 👎.}