ControlMode(fix[client_name]): bind client name to spawned client

why: recording the first client returned by list-clients can capture an existing
attached client instead of the control-mode client spawned for the test.
what:
- wait for the spawned client pid to appear in list-clients
- record client_name from the matching pid row
- add a nested control-mode regression that verifies pid-to-name binding

Author: tony

src/libtmux/_internal/control_mode.py

@@ -91,22 +91,24 @@ def __enter__(self) -> ControlMode:
         self._write_fd = os.open(self._fifo_path, os.O_WRONLY)
 
         self.stdout = self._proc.stdout  # type: ignore[assignment]
+        client_pid = str(self._proc.pid)
 
         # Wait for client to register
         def client_registered() -> bool:
-            clients = self.server.list_clients()
-            return len(clients) > 0
+            result = self.server.cmd(
+                "list-clients",
+                "-F",
+                "#{client_pid}\t#{client_name}",
+            )
+            for line in result.stdout:
+                pid, _, client_name = line.partition("\t")
+                if pid == client_pid and client_name:
+                    self.client_name = client_name.strip()
+                    return True
+            return False
 
         retry_until(client_registered, 3, raises=True)
 
-        # Capture client name
-        result = self.server.cmd(
-            "list-clients",
-            "-F",
-            "#{client_name}",
-        )
-        self.client_name = result.stdout[0].strip() if result.stdout else ""
-
         return self
 
     def __exit__(

tests/test_control_mode.py

@@ -40,3 +40,23 @@ def test_control_mode_client_name(
     """ControlMode.client_name contains the tmux client identifier."""
     with control_mode() as ctl:
         assert "client-" in ctl.client_name
+
+
+def test_control_mode_client_name_matches_spawned_client(
+    control_mode: t.Callable[[], ControlMode],
+    server: Server,
+) -> None:
+    """ControlMode records the client name for its own subprocess."""
+    with control_mode() as first, control_mode() as second:
+        clients = {
+            tuple(line.split("\t", 1))
+            for line in server.cmd(
+                "list-clients",
+                "-F",
+                "#{client_pid}\t#{client_name}",
+            ).stdout
+        }
+
+        assert first.client_name != second.client_name
+        assert (str(first._proc.pid), first.client_name) in clients
+        assert (str(second._proc.pid), second.client_name) in clients