neo(docs[fetch_objs]): Add NumPy-style docstring with doctest

why: CLAUDE.md requires NumPy-style docstrings for all functions;
fetch_objs() was modified in this branch but only had a one-liner.
what:
- Add Parameters, Returns, Raises, and Examples sections
- Add working doctest using server fixture

Author: tony

src/libtmux/neo.py

@@ -242,7 +242,44 @@ def fetch_objs(
     list_cmd: ListCmd,
     list_extra_args: ListExtraArgs = None,
 ) -> OutputsRaw:
-    """Fetch a listing of raw data from a tmux command."""
+    """Fetch a listing of raw data from a tmux command.
+
+    Runs a tmux list command (e.g. ``list-sessions``) with the format string
+    from :func:`get_output_format` and parses each line of output into a dict.
+
+    Parameters
+    ----------
+    server : :class:`~libtmux.server.Server`
+        The tmux server to query.
+    list_cmd : ListCmd
+        The tmux list command to run, e.g. ``"list-sessions"``,
+        ``"list-windows"``, or ``"list-panes"``.
+    list_extra_args : ListExtraArgs, optional
+        Extra arguments appended to the tmux command (e.g. ``("-a",)``
+        for all windows/panes, or ``["-t", session_id]`` to filter).
+
+    Returns
+    -------
+    OutputsRaw
+        A list of dicts, each mapping tmux format field names to their
+        non-empty string values.
+
+    Raises
+    ------
+    :exc:`~libtmux.exc.LibTmuxException`
+        If the tmux command writes to stderr.
+
+    Examples
+    --------
+    >>> from libtmux.neo import fetch_objs
+    >>> objs = fetch_objs(server=server, list_cmd="list-sessions")
+    >>> isinstance(objs, list)
+    True
+    >>> isinstance(objs[0], dict)
+    True
+    >>> 'session_id' in objs[0]
+    True
+    """
     _fields, format_string = get_output_format()
 
     cmd_args: list[str | int] = []

src/libtmux/server.py

@@ -578,7 +578,8 @@ def new_session(
             raise exc.LibTmuxException(proc.stderr)
 
         if not proc.stdout:
-            raise exc.LibTmuxException("new-session produced no output")
+            msg = "new-session produced no output"
+            raise exc.LibTmuxException(msg)
 
         session_stdout = proc.stdout[0]