diff --git a/tests/tui_gateway/test_project_tree.py b/tests/tui_gateway/test_project_tree.py
index 0faeac7f1e..69fc2b0176 100644
--- a/tests/tui_gateway/test_project_tree.py
+++ b/tests/tui_gateway/test_project_tree.py
@@ -561,3 +561,35 @@ def test_colliding_repo_basenames_disambiguate_labels():
     labels = sorted(p["label"] for p in tree["projects"])
 
     assert labels == ["x/proj", "y/proj"]
+
+
+def test_non_git_folder_uses_branch_lane_id():
+    """#53329: _place_by_heuristic must use _branch_lane_id for non-git folders.
+
+    Before the fix, non-git folders got a lane key equal to the raw path,
+    while the desktop overlay expected ::branch::main. This caused duplicate
+    lanes (one from backend, one from overlay).
+    """
+    result = pt._place_by_heuristic("/home/user/my-project")
+    assert result is not None
+    assert result["lane_key"] == pt._branch_lane_id(
+        "/home/user/my-project", pt.DEFAULT_BRANCH_LABEL
+    ), (
+        f"Expected lane_key to use _branch_lane_id scheme but got "
+        f"{result['lane_key']!r}"
+    )
+    # The label should still be the folder basename
+    assert result["lane_label"] == "my-project"
+    # Must be marked as main lane
+    assert result["is_main"] is True
+
+
+def test_non_git_folder_lane_matches_overlay_scheme():
+    """#53329: verify the lane key format matches what the overlay expects."""
+    result = pt._place_by_heuristic("/data/work/folder-x")
+    assert result is not None
+    # Overlay expects: <path>::branch::main
+    expected = "/data/work/folder-x::branch::main"
+    assert result["lane_key"] == expected, (
+        f"Expected lane_key={expected!r} but got {result['lane_key']!r}"
+    )
diff --git a/tui_gateway/project_tree.py b/tui_gateway/project_tree.py
index cd5c966a55..5a92b38c97 100644
--- a/tui_gateway/project_tree.py
+++ b/tui_gateway/project_tree.py
@@ -221,7 +221,7 @@ def _place_by_heuristic(path: str) -> Optional[dict]:
         repo_path = _with_base_name(path, m.group(1))
         return _placement(repo_path, path, m.group(2), path, False, False)
 
-    return _placement(path, path, base, path, True, False)
+    return _placement(path, _branch_lane_id(path, DEFAULT_BRANCH_LABEL), base, path, True, False)
 
 
 def _place(cwd: str, branch: str, resolve: Optional[Resolve], persisted_root: str) -> Optional[dict]: