feat(tmux-util): add find subcommand

tmux-util find <pattern> walks every pane across every session, queries each pane's foreground command (`#{pane_current_command}`), and prints the location of any pane whose command matches the pattern. Output format: `<session>:<window>.<pane> <command>`, one per line.

Pattern is a basic ERE (passed through `grep -E`), so anchors and alternation work. Substring matching is the common case.

Exit code:
- 0 with output: matches found
- 1 with no output: no matches (lets you script around it)
- 2 with usage on stderr: missing or empty pattern

7 new tests cover Normal cases (single match, multi-match across sessions, format verification) and Boundary cases (no matches, no sessions, missing pattern, empty pattern). fake-tmux now parses pid:cmd entries in the state file so panes can carry a synthetic command name. Total suite: 39 tests, all green.

1 files changed, 72 insertions, 0 deletions

diff --git a/tests/tmux-util/test_tmux_util.py b/tests/tmux-util/test_tmux_util.py
index 24cc335..e313af6 100644
--- a/tests/tmux-util/test_tmux_util.py
+++ b/tests/tmux-util/test_tmux_util.py
@@ -477,5 +477,77 @@ class TestGoErrors(TmuxUtilHarness):
         self.assertIn("missing session name", result.stderr)
 
 
+# -----------------------------------------------------------------------------
+# find — Normal cases
+# -----------------------------------------------------------------------------
+
+class TestFindNormal(TmuxUtilHarness):
+
+    def test_find_matches_pane_running_named_command(self):
+        # Two sessions, one has a pane running vim; find should locate it.
+        self.set_sessions([
+            ("work", 1, ["101:zsh", "102:vim"], 950, 2, "/tmp/work"),
+            ("idle", 0, ["201:zsh"], 900, 1, "/tmp/idle"),
+        ])
+        result = self.run_script("find", "vim")
+        self.assertEqual(result.returncode, 0, msg=result.stderr)
+        self.assertIn("work:", result.stdout)
+        self.assertIn("vim", result.stdout)
+        # idle session pane shouldn't be in the output
+        self.assertNotIn("idle:", result.stdout)
+
+    def test_find_matches_multiple_panes(self):
+        self.set_sessions([
+            ("a", 1, ["101:zsh", "102:vim"], 950, 1, "/tmp/a"),
+            ("b", 1, ["201:vim"], 900, 1, "/tmp/b"),
+        ])
+        result = self.run_script("find", "vim")
+        self.assertEqual(result.returncode, 0)
+        self.assertIn("a:", result.stdout)
+        self.assertIn("b:", result.stdout)
+        # Two matches, two output lines
+        lines = [ln for ln in result.stdout.strip().split("\n") if ln]
+        self.assertEqual(len(lines), 2, msg=f"expected 2 matching lines, got {lines!r}")
+
+    def test_find_output_includes_session_window_pane_location(self):
+        self.set_sessions([
+            ("work", 1, ["101:zsh", "102:vim"], 950, 1, "/tmp/work"),
+        ])
+        result = self.run_script("find", "vim")
+        self.assertEqual(result.returncode, 0)
+        # Expected format: work:0.1 vim  (window 0, pane index 1)
+        self.assertRegex(result.stdout, r"work:0\.1\s+vim")
+
+
+# -----------------------------------------------------------------------------
+# find — Boundary / Error cases
+# -----------------------------------------------------------------------------
+
+class TestFindBoundary(TmuxUtilHarness):
+
+    def test_find_no_matches_exits_nonzero(self):
+        self.set_sessions([
+            ("work", 1, ["101:zsh"], 950, 1, "/tmp/work"),
+        ])
+        result = self.run_script("find", "nothing-matches-this")
+        self.assertNotEqual(result.returncode, 0)
+        self.assertEqual(result.stdout.strip(), "")
+
+    def test_find_no_sessions_exits_nonzero(self):
+        self.set_sessions([])
+        result = self.run_script("find", "vim")
+        self.assertNotEqual(result.returncode, 0)
+
+    def test_find_no_pattern_exits_nonzero(self):
+        result = self.run_script("find")
+        self.assertNotEqual(result.returncode, 0)
+        self.assertIn("missing pattern", result.stderr)
+
+    def test_find_empty_pattern_exits_nonzero(self):
+        result = self.run_script("find", "")
+        self.assertNotEqual(result.returncode, 0)
+        self.assertIn("missing pattern", result.stderr)
+
+
 if __name__ == "__main__":
     unittest.main()