fix: restore interactive PTY behavior

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a03397-4d51-7fd1-8ff2-946eb22ea2bc

src/tamq/control.py

@@ -16,16 +16,29 @@ class ControlModeClient:
     tmux_command: Sequence[str] | None = None
     process: subprocess.Popen[str] | None = None
 
-    def start(self) -> None:
-        if self.process is not None:
-            return
+    def _command(self) -> tuple[str, ...]:
         socket_name = os.environ.get("TAMQ_TMUX_SOCKET")
-        command = tuple(
+        return tuple(
             self.tmux_command
             or (["tmux", "-L", socket_name] if socket_name else ["tmux"])
         )
+
+    def session_exists(self, expected_pid: int | None = None) -> bool:
+        result = subprocess.run(
+            [*self._command(), "display-message", "-p", "-t", self.session, "#{pid}"],
+            text=True,
+            capture_output=True,
+            check=False,
+        )
+        if result.returncode != 0:
+            return False
+        return expected_pid is None or result.stdout.strip() == str(expected_pid)
+
+    def start(self) -> None:
+        if self.process is not None:
+            return
         self.process = subprocess.Popen(
-            [*command, "-C", "attach-session", "-t", self.session],
+            [*self._command(), "-C", "attach-session", "-t", self.session],
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,