fix: reuse cached config profile git mounts

- Reuse valid deterministic git mount clones on repeated starts
- Remove incomplete clone destinations before retrying
- Add regression coverage for cached and partial clones
- Document OpenSpec change fix-config-profile-git-mount-clone-reuse

Quality gates: pytest (13 passed), ruff, mypy

apps/api/src/services/tool/instance_service.py

@@ -283,16 +283,27 @@ def clone_git_repo(
     url_hash = hashlib.md5(f"{remote_url}:{branch_segment}".encode()).hexdigest()[:12]
     repo_name = remote_url.split("/")[-1].replace(".git", "") or "repo"
     clone_dir = os.path.join(clone_parent, "git-mounts", f"{repo_name}-{url_hash}")
-    repo_path = clone_repository(
-        remote_url,
-        None,  # No SSH key for now - can be added later
-        clone_dir,
-        branch or "main",
-        project_name=project_name,
-    )
+    clone_name = _slugify_directory_name(project_name) if project_name else "repo-clone"
+    repo_path = os.path.join(clone_dir, clone_name)
 
-    if not os.path.exists(repo_path):
+    if os.path.isdir(os.path.join(repo_path, ".git")):
+        # Reuse the deterministic per-repository cache on repeated starts.
         try:
+            pull_repository_updates(repo_path, remote_url)
+            logger.debug("Pulled updates for git mount %s", remote_url)
+        except Exception as exc:
+            logger.warning("Failed to pull updates for %s: %s", remote_url, exc)
+    else:
+        try:
+            # A failed clone can leave its destination behind. Remove only the
+            # computed clone path so the next start can retry cleanly.
+            if os.path.lexists(repo_path):
+                logger.warning("Removing incomplete git mount clone at %s", repo_path)
+                if os.path.isdir(repo_path) and not os.path.islink(repo_path):
+                    shutil.rmtree(repo_path)
+                else:
+                    os.unlink(repo_path)
+
             os.makedirs(clone_dir, exist_ok=True)
             repo_path = clone_repository(
                 remote_url,
@@ -305,13 +316,6 @@ def clone_git_repo(
         except Exception as exc:
             logger.warning("Clone failed for git mount %s: %s", remote_url, exc)
             raise
-    else:
-        # Repo exists - pull latest updates
-        try:
-            pull_repository_updates(repo_path, remote_url)
-            logger.debug("Pulled updates for git mount %s", remote_url)
-        except Exception as exc:
-            logger.warning("Failed to pull updates for %s: %s", remote_url, exc)
 
     # Handle branch checkout if specified
     if branch and repo_path: