feat: replace global issue lock with keyed persistent store (Closes #443)

Store per remote/org/repo/issue locks under GITEA_ISSUE_LOCK_DIR with
atomic writes and per-session binding. Integrate own-branch adoption for
lock recovery, update worktree-start and cleanup reconcile, and add tests
documenting the ban on manual global lock seeding.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_agent_temp_artifacts.py

@@ -74,11 +74,14 @@ ISSUE_WRITE_ENV = {
 
 class TestIssueLockArtifactWarning(unittest.TestCase):
     def setUp(self):
-        self._env_patcher = patch.dict(os.environ, ISSUE_WRITE_ENV, clear=True)
+        self._lock_dir = tempfile.TemporaryDirectory()
+        env = {**ISSUE_WRITE_ENV, "GITEA_ISSUE_LOCK_DIR": self._lock_dir.name}
+        self._env_patcher = patch.dict(os.environ, env, clear=True)
         self._env_patcher.start()
 
     def tearDown(self):
         self._env_patcher.stop()
+        self._lock_dir.cleanup()
 
     @patch(
         "mcp_server.issue_duplicate_context_fetcher",
@@ -86,9 +89,8 @@ class TestIssueLockArtifactWarning(unittest.TestCase):
     )
     @patch("mcp_server._auth", return_value="token x")
     @patch("mcp_server._resolve", return_value=("h", "o", "r"))
-    @patch("mcp_server.ISSUE_LOCK_FILE", new_callable=lambda: tempfile.mktemp())
     @patch("issue_lock_worktree.read_worktree_git_state")
-    def test_lock_success_includes_artifact_warning(self, mock_state, _lock_file, *_mocks):
+    def test_lock_success_includes_artifact_warning(self, mock_state, *_mocks):
         mock_state.return_value = {
             "current_branch": "master",
             "porcelain_status": "?? _emit_payload.py\n",