Fix race condition in new_session() by avoiding list-sessions query

Previously, new_session() would run 'tmux new-session -P -F#{session_id}'
then immediately query 'tmux list-sessions' to fetch full session data.
This created a race condition in PyInstaller + Python 3.13+ + Docker
environments where list-sessions might not see the newly created session.

The fix expands the -F format string to include all Obj fields, parsing
the output directly into a Session object without a separate query.

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

src/libtmux/neo.py

@@ -177,6 +177,22 @@ def _refresh(
                 setattr(self, k, v)
 
 
+def get_output_format() -> tuple[list[str], str]:
+    """Return field names and tmux format string for all Obj fields."""
+    # Exclude 'server' - it's a Python object, not a tmux format variable
+    formats = [f for f in Obj.__dataclass_fields__.keys() if f != "server"]
+    tmux_formats = [f"#{{{f}}}{FORMAT_SEPARATOR}" for f in formats]
+    return formats, "".join(tmux_formats)
+
+
+def parse_output(output: str) -> OutputRaw:
+    """Parse tmux output formatted with get_output_format() into a dict."""
+    # Exclude 'server' - it's a Python object, not a tmux format variable
+    formats = [f for f in Obj.__dataclass_fields__.keys() if f != "server"]
+    formatter = dict(zip(formats, output.split(FORMAT_SEPARATOR), strict=False))
+    return {k: v for k, v in formatter.items() if v}
+
+
 def fetch_objs(
     server: Server,
     list_cmd: ListCmd,

src/libtmux/server.py

@@ -19,7 +19,7 @@
 from libtmux.common import tmux_cmd
 from libtmux.constants import OptionScope
 from libtmux.hooks import HooksMixin
-from libtmux.neo import fetch_objs
+from libtmux.neo import fetch_objs, get_output_format, parse_output
 from libtmux.pane import Pane
 from libtmux.session import Session
 from libtmux.window import Window
@@ -539,9 +539,11 @@ def new_session(
         if env:
             del os.environ["TMUX"]
 
+        _fields, format_string = get_output_format()
+
         tmux_args: tuple[str | int, ...] = (
             "-P",
-            "-F#{session_id}",  # output
+            f"-F{format_string}",
         )
 
         if session_name is not None:
@@ -580,18 +582,9 @@ def new_session(
         if env:
             os.environ["TMUX"] = env
 
-        session_formatters = dict(
-            zip(
-                ["session_id"],
-                session_stdout.split(formats.FORMAT_SEPARATOR),
-                strict=False,
-            ),
-        )
+        session_data = parse_output(session_stdout)
 
-        return Session.from_session_id(
-            server=self,
-            session_id=session_formatters["session_id"],
-        )
+        return Session(server=self, **session_data)
 
     #
     # Relations