libtmux(test[logging]): add logging schema test

why: Verify structured logging contract per AGENTS.md testing standards.
what:
- Add test_tmux_cmd_debug_logging_schema asserting tmux_cmd and
  tmux_exit_code extra fields on log records from common.tmux_cmd
- Uses caplog.records attributes (not caplog.text) per standards

Author: tony

tests/test_logging.py

@@ -0,0 +1,25 @@
+"""Tests for libtmux logging standards compliance."""
+
+from __future__ import annotations
+
+import logging
+import typing as t
+
+import pytest
+
+if t.TYPE_CHECKING:
+    from libtmux.server import Server
+
+
+def test_tmux_cmd_debug_logging_schema(
+    server: Server,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Test that tmux_cmd produces structured log records per AGENTS.md."""
+    with caplog.at_level(logging.DEBUG, logger="libtmux.common"):
+        server.cmd("list-sessions")
+    records = [r for r in caplog.records if hasattr(r, "tmux_cmd")]
+    assert len(records) >= 1
+    record = records[0]
+    assert isinstance(getattr(record, "tmux_cmd"), str)
+    assert isinstance(getattr(record, "tmux_exit_code"), int)