fix: use ASCII tmux format separator on Windows

README.md

@@ -60,6 +60,18 @@ Add this to your `mcp.json` (e.g., in Claude Desktop, Cursor, or 1mcp):
 
 *Note: If you installed via `uv tool install`, you can just use `mcp-ssh-tmux` as the command.*
 
+### Native Windows tmux compatibility
+
+On Windows, the server defaults `LIBTMUX_TMUX_FORMAT_SEPARATOR` to the ASCII
+marker `|__LIBTMUX_SEP__|` before importing libtmux. Native Windows tmux builds
+can replace libtmux's default Unicode separator (`␞`) with `?`, causing
+`list_sessions` and other operations to fail with
+`zip() argument 2 is shorter than argument 1`.
+
+An explicitly configured `LIBTMUX_TMUX_FORMAT_SEPARATOR` is preserved; use an
+ASCII marker that will not appear in tmux field values. Other platforms keep
+libtmux's default. Restart the MCP server after changing the environment.
+
 ## Tools
 
 -   `open_session(host, username, port)`: Opens a new SSH connection in a unique tmux window.

mcp_ssh_tmux/__init__.py

@@ -0,0 +1,10 @@
+"""Package initialization and platform compatibility defaults."""
+
+import os
+import sys
+
+# Configure this before importing libtmux: its format separator is read once
+# at import time. Native Windows tmux can replace the default Unicode U+241E
+# separator with '?', causing libtmux's strict field parsing to fail.
+if sys.platform == "win32":
+    os.environ.setdefault("LIBTMUX_TMUX_FORMAT_SEPARATOR", "|__LIBTMUX_SEP__|")

tests/test_platform_compat.py

@@ -0,0 +1,64 @@
+"""Test platform defaults in fresh processes without starting tmux or SSH."""
+
+import os
+from pathlib import Path
+import subprocess
+import sys
+
+import pytest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+ENV_KEY = "LIBTMUX_TMUX_FORMAT_SEPARATOR"
+
+
+@pytest.mark.parametrize(
+    ("platform", "configured", "expected"),
+    [
+        ("win32", None, "|__LIBTMUX_SEP__|"),
+        ("win32", "custom-separator", "custom-separator"),
+        ("linux", None, None),
+        ("darwin", None, None),
+        ("linux", "custom-separator", "custom-separator"),
+    ],
+)
+def test_platform_separator_default(platform, configured, expected):
+    env = os.environ.copy()
+    env.pop(ENV_KEY, None)
+    if configured is not None:
+        env[ENV_KEY] = configured
+    script = f"""
+import os
+import sys
+sys.platform = {platform!r}
+import mcp_ssh_tmux
+assert os.environ.get({ENV_KEY!r}) == {expected!r}
+"""
+    subprocess.run([sys.executable, "-c", script], cwd=ROOT, env=env, check=True)
+
+
+def test_windows_separator_survives_lossy_encoding_and_parses():
+    env = os.environ.copy()
+    env.pop(ENV_KEY, None)
+    script = """
+import sys
+platform = sys.platform
+sys.platform = 'win32'
+import mcp_ssh_tmux
+sys.platform = platform
+from libtmux.formats import FORMAT_SEPARATOR
+from libtmux.neo import get_output_format, parse_output
+from inspect import signature
+assert FORMAT_SEPARATOR == '|__LIBTMUX_SEP__|'
+for command in ('list-sessions', 'list-windows', 'list-panes'):
+    # Older libtmux releases use one format for all listing commands.
+    kwargs = {'list_cmd': command, 'tmux_version': '3.6a'} if 'list_cmd' in signature(get_output_format).parameters else {}
+    fields, template = get_output_format(**kwargs)
+    assert template.encode('ascii', errors='replace').decode('ascii') == template
+    values = ['test' if field == 'session_name' else '' for field in fields]
+    output = FORMAT_SEPARATOR.join(values) + FORMAT_SEPARATOR
+    output = output.encode('ascii', errors='replace').decode('ascii')
+    parsed = parse_output(output, **kwargs)
+    assert parsed['session_name'] == 'test'
+"""
+    subprocess.run([sys.executable, "-c", script], cwd=ROOT, env=env, check=True)