fix(maestro): recognise tmux 3.7's "server exited unexpectedly"

Killing the last session shuts the server down, and tmux >= 3.7 reports
that to the still-connected client with a phrasing `is_no_server_error`
did not match. `list_sessions` then returned Err, and `run_liveness_pass`
logs a warning and returns — so the pass reaped nothing.

Silent by construction: nothing asserted the phrasing set, and the only
symptom was an integration test that looked flaky. Both now covered.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/maestro-daemon/src/tmux.rs

@@ -263,12 +263,22 @@ impl Tmux {
     }
 }
 
+/// Phrasings tmux uses for "there is no server on this socket". They vary by
+/// version, and `list_sessions` turning one of these into an `Err` stops the
+/// liveness watcher reaping for that pass — so a missing phrasing is silent.
+const NO_SERVER_PHRASES: &[&str] = &[
+    "no server running",
+    "no sessions",
+    "error connecting",
+    // tmux >= 3.7 when the server shuts down while this client is connected,
+    // which is exactly what killing the last session does.
+    "server exited unexpectedly",
+];
+
 /// True if tmux's stderr indicates "there is no tmux server running on this
 /// socket" (multiple phrasings across versions).
 fn is_no_server_error(stderr: &str) -> bool {
-    stderr.contains("no server running")
-        || stderr.contains("no sessions")
-        || stderr.contains("error connecting")
+    NO_SERVER_PHRASES.iter().any(|p| stderr.contains(p))
 }
 
 /// A session pane's process id, foreground command, controlling tty, and
@@ -407,6 +417,26 @@ fn check(out: Output) -> Result<(), TmuxError> {
 mod tests {
     use super::*;
 
+    /// Every phrasing must be recognised: an unmatched one makes
+    /// `list_sessions` fail, and a failed pass reaps nothing.
+    #[test]
+    fn is_no_server_error_matches_every_known_phrasing() {
+        for phrase in NO_SERVER_PHRASES {
+            assert!(is_no_server_error(phrase), "unmatched: {phrase}");
+            assert!(
+                is_no_server_error(&format!("{phrase}\n")),
+                "unmatched with trailing newline: {phrase}"
+            );
+        }
+    }
+
+    #[test]
+    fn is_no_server_error_rejects_unrelated_failures() {
+        assert!(!is_no_server_error("can't find session: maestro-x"));
+        assert!(!is_no_server_error("usage: kill-session"));
+        assert!(!is_no_server_error(""));
+    }
+
     #[test]
     fn parse_pane_line_splits_pid_command_tty_path() {
         let p = parse_pane_line("12345 claude /dev/pts/3 /home/naps62/maestro").unwrap();