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_commit_payloads.py

@@ -66,7 +66,10 @@ class TestCommitPayloads(unittest.TestCase):
         )
         self.locked_worktree_path = os.path.realpath(self.locked_worktree_dir.name)
 
-        self.lock_file_path = "/tmp/gitea_issue_lock.json"
+        import issue_lock_store
+
+        self._lock_dir = tempfile.TemporaryDirectory()
+        os.environ["GITEA_ISSUE_LOCK_DIR"] = self._lock_dir.name
         self.lock_data = {
             "issue_number": 263,
             "branch_name": "feat/issue-263-native-commit-payloads",
@@ -74,9 +77,12 @@ class TestCommitPayloads(unittest.TestCase):
             "org": "Example-Org",
             "repo": "Example-Repo",
             "worktree_path": self.locked_worktree_path,
+            "work_lease": {
+                "operation_type": "author_issue_work",
+                "expires_at": "2999-01-01T00:00:00Z",
+            },
         }
-        with open(self.lock_file_path, "w", encoding="utf-8") as fh:
-            fh.write(json.dumps(self.lock_data))
+        self.lock_file_path = issue_lock_store.bind_session_lock(self.lock_data)
 
         # Reset preflight status to bypass/pass verification in tests
         self.orig_whoami_called = mcp_server._preflight_whoami_called
@@ -93,8 +99,7 @@ class TestCommitPayloads(unittest.TestCase):
 
         self._dir.cleanup()
         self.locked_worktree_dir.cleanup()
-        if os.path.exists(self.lock_file_path):
-            os.remove(self.lock_file_path)
+        self._lock_dir.cleanup()
 
     def _env(self, profile: str) -> dict:
         return {
@@ -103,6 +108,7 @@ class TestCommitPayloads(unittest.TestCase):
             "GITEA_TOKEN_AUTHOR": "author-pass",
             "GITEA_TEST_PORCELAIN": "",
             "GITEA_AUTHOR_WORKTREE": self.locked_worktree_path,
+            "GITEA_ISSUE_LOCK_DIR": self._lock_dir.name,
         }
 
     @patch("mcp_server.api_request")