feat(cli): lock hermes worktrees so concurrent processes can't clobber them

git worktree lock at creation and unlock before removal. A locked
worktree refuses 'git worktree remove' (and prune), so a second hermes
process or a stray cleanup can't silently delete an in-use isolated
worktree. Fail-soft on both paths — a lock/unlock error never blocks
the session or cleanup.

Salvaged from #47029 (Issue #46303). Unlock moved to the actual-removal
path so a preserved (unpushed-commits) worktree stays locked while in use.

cli.py

@@ -1340,6 +1340,17 @@ def _setup_worktree(repo_root: str = None) -> Optional[Dict[str, str]]:
         except Exception as e:
             logger.debug("Error copying .worktreeinclude entries: %s", e)
 
+    # Lock the worktree so other processes (and `git worktree remove`) can see
+    # it is actively in use.  Fail-soft: a lock failure never blocks the session.
+    try:
+        subprocess.run(
+            ["git", "worktree", "lock", "--reason", f"hermes pid={os.getpid()}", str(wt_path)],
+            capture_output=True, text=True, timeout=10, cwd=repo_root,
+        )
+        logger.debug("Worktree locked: %s (pid=%s)", wt_path, os.getpid())
+    except Exception as e:
+        logger.debug("git worktree lock failed (non-fatal): %s", e)
+
     info = {
         "path": str(wt_path),
         "branch": branch_name,
@@ -1415,6 +1426,16 @@ def _cleanup_worktree(info: Dict[str, str] = None) -> None:
 
     # Remove worktree (even if working tree is dirty — uncommitted
     # changes without unpushed commits are just artifacts)
+    # Unlock first so `git worktree remove` isn't blocked by the lock we
+    # placed at creation time.  Fail-soft — never block cleanup.
+    try:
+        subprocess.run(
+            ["git", "worktree", "unlock", wt_path],
+            capture_output=True, text=True, timeout=10, cwd=repo_root,
+        )
+    except Exception as e:
+        logger.debug("git worktree unlock failed (non-fatal): %s", e)
+
     try:
         subprocess.run(
             ["git", "worktree", "remove", wt_path, "--force"],