marker: add direction-clear, routing, and ubridge transport tests

Close the test gaps surfaced in review:

- controller (test_marker.py): direction clear vs preserve, definition-sync
  clear propagation, pinned-marker NIO routing, _markers_for_node carrying
  direction, and non-capable capture-node rejection.
- ubridge (new tests/compute/ubridge/test_hypervisor.py): unix/tcp __init__
  branches + socket-dir perms, _build_command -U/-H/debug, endpoint, stop
  socket unlink, and start() immediate-exit fail-fast.
- mcp (test_handlers.py): TestLinkMarker / TestMarkerDefinition covering
  direction tri-state (both/tx/omitted) for create and update.

tests/compute/ubridge/test_hypervisor.py

@@ -0,0 +1,191 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2025 GNS3 Technologies Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Tests for the uBridge ``Hypervisor`` wrapper — the configurable control-channel
+transport (AF_UNIX ``-U`` vs TCP ``-H``), command building, the human-readable
+``endpoint``, socket cleanup on stop, and the fail-fast detection of an
+immediately-exiting uBridge process (e.g. an old build that rejects ``-U``).
+"""
+
+import os
+import re
+import stat
+import logging
+
+import pytest
+from unittest.mock import MagicMock, AsyncMock, patch
+
+from gns3server.compute.ubridge.hypervisor import Hypervisor
+from gns3server.compute.ubridge.ubridge_error import UbridgeError
+
+
+def _make(transport, tmp_path, monkeypatch, node_id="abc123", host="127.0.0.1"):
+    """Build a Hypervisor with ``XDG_RUNTIME_DIR`` pinned to ``tmp_path``.
+
+    The unix transport creates its socket dir under ``$XDG_RUNTIME_DIR/gns3``;
+    pinning it keeps creation predictable and avoids touching the real runtime
+    dir. ``host`` is unused for the unix transport but always accepted.
+    """
+
+    monkeypatch.setenv("XDG_RUNTIME_DIR", str(tmp_path))
+    return Hypervisor(MagicMock(), "ubridge", str(tmp_path), transport, host=host, node_id=node_id)
+
+
+# ---------------------------------------------------------------------------
+# __init__: transport selection
+# ---------------------------------------------------------------------------
+
+def test_init_unix_creates_socket_dir_and_path(tmp_path, monkeypatch):
+
+    hyp = _make("unix", tmp_path, monkeypatch, node_id="abc123")
+    assert hyp._socket_path == str(tmp_path / "gns3" / "ubridge-abc123.sock")
+
+    socket_dir = os.path.dirname(hyp._socket_path)
+    assert os.path.isdir(socket_dir)
+    # 0o700 regardless of umask — __init__ chmods explicitly.
+    assert stat.S_IMODE(os.stat(socket_dir).st_mode) == 0o700
+    # TCP-only attributes are unused on the unix transport.
+    assert hyp._host is None
+    assert hyp._port is None
+
+
+def test_init_unix_fallback_name_without_node_id(tmp_path, monkeypatch):
+    # node_id is normally always passed (one ubridge per node); the counter
+    # fallback only fires when it's missing. Match the numbered pattern so the
+    # assertion is independent of class-counter ordering across the suite.
+    hyp = _make("unix", tmp_path, monkeypatch, node_id=None)
+    assert re.search(r"ubridge-\d+\.sock$", hyp._socket_path)
+
+
+def test_init_tcp_sets_host_port(tmp_path, monkeypatch):
+
+    hyp = _make("tcp", tmp_path, monkeypatch)
+    assert hyp._socket_path is None
+    assert hyp._host == "127.0.0.1"
+    assert isinstance(hyp._port, int) and hyp._port > 0
+
+
+# ---------------------------------------------------------------------------
+# _build_command + endpoint
+# ---------------------------------------------------------------------------
+
+def test_build_command_unix(tmp_path, monkeypatch):
+
+    hyp = _make("unix", tmp_path, monkeypatch)
+    cmd = hyp._build_command()
+    assert cmd[0] == "ubridge"
+    assert "-U" in cmd
+    assert hyp._socket_path in cmd
+    assert "-H" not in cmd
+    assert "-d" not in cmd  # debug flag only at DEBUG level
+
+
+def test_build_command_tcp(tmp_path, monkeypatch):
+
+    hyp = _make("tcp", tmp_path, monkeypatch)
+    cmd = hyp._build_command()
+    assert cmd[0] == "ubridge"
+    assert "-H" in cmd
+    assert f"{hyp._host}:{hyp._port}" in cmd
+    assert "-U" not in cmd
+
+
+def test_build_command_debug_flag(tmp_path, monkeypatch):
+
+    hyp = _make("unix", tmp_path, monkeypatch)
+    logger = logging.getLogger("gns3server.compute.ubridge.hypervisor")
+    original = logger.level
+    logger.setLevel(logging.DEBUG)
+    try:
+        cmd = hyp._build_command()
+        assert "-d" in cmd and "1" in cmd
+    finally:
+        logger.setLevel(original)
+
+
+def test_endpoint_unix(tmp_path, monkeypatch):
+
+    hyp = _make("unix", tmp_path, monkeypatch)
+    assert hyp.endpoint == hyp._socket_path
+
+
+def test_endpoint_tcp(tmp_path, monkeypatch):
+
+    hyp = _make("tcp", tmp_path, monkeypatch)
+    assert hyp.endpoint == f"{hyp._host}:{hyp._port}"
+
+
+# ---------------------------------------------------------------------------
+# stop: AF_UNIX socket cleanup
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_stop_unlinks_unix_socket(tmp_path, monkeypatch):
+
+    hyp = _make("unix", tmp_path, monkeypatch)
+    # Simulate the socket file ubridge would have created.
+    open(hyp._socket_path, "w").close()
+    # Stopped process => is_running() is False => skips UBridgeHypervisor.stop (no send).
+    hyp._process = MagicMock()
+    hyp._process.returncode = 0
+    assert os.path.exists(hyp._socket_path)
+
+    await hyp.stop()
+
+    assert not os.path.exists(hyp._socket_path)
+
+
+@pytest.mark.asyncio
+async def test_stop_tcp_has_no_socket_to_unlink(tmp_path, monkeypatch):
+    # TCP transport: no socket_path, so stop must simply not raise.
+    hyp = _make("tcp", tmp_path, monkeypatch)
+    hyp._process = MagicMock()
+    hyp._process.returncode = 0
+    await hyp.stop()
+
+
+# ---------------------------------------------------------------------------
+# start: fail-fast on an immediately-exiting uBridge
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_start_detects_immediate_exit(tmp_path, monkeypatch):
+    # An unsupported flag (e.g. -U on an old ubridge) makes the process exit at
+    # once. start() must surface that from ubridge.log instead of timing out in
+    # connect() with a confusing "couldn't connect" error.
+    hyp = _make("unix", tmp_path, monkeypatch)
+    proc = MagicMock()
+    proc.pid = 1234
+    proc.returncode = 2  # already exited
+    with patch.object(Hypervisor, "_check_ubridge_version", new_callable=AsyncMock), \
+         patch("asyncio.create_subprocess_exec", new_callable=AsyncMock, return_value=proc):
+        with pytest.raises(UbridgeError, match="exited immediately"):
+            await hyp.start()
+
+
+@pytest.mark.asyncio
+async def test_start_proceeds_when_process_keeps_running(tmp_path, monkeypatch):
+    # Healthy startup: the process stays up, so start() returns normally.
+    hyp = _make("unix", tmp_path, monkeypatch)
+    proc = MagicMock()
+    proc.pid = 1234
+    proc.returncode = None  # still running
+    with patch.object(Hypervisor, "_check_ubridge_version", new_callable=AsyncMock), \
+         patch("asyncio.create_subprocess_exec", new_callable=AsyncMock, return_value=proc):
+        await hyp.start()  # must NOT raise
+    assert hyp._process is proc