fix(extensions): make LOCAL_EXTENSIONS hot reload reliable in Docker (#40084)

Co-authored-by: Amin Ghadersohi <amin.ghadersohi@gmail.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

tests/unit_tests/extensions/test_local_extensions_watcher.py

@@ -0,0 +1,59 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from typing import Any
+
+from watchdog.events import FileDeletedEvent, FileMovedEvent
+
+from superset.extensions.local_extensions_watcher import _get_file_handler_class
+
+
+def _noop_schedule_reload(_path: str) -> None:
+    """Stand in for a real debounce timer in unit tests."""
+
+
+def make_handler() -> Any:
+    handler_class = _get_file_handler_class()
+    handler = handler_class()
+    # Avoid spinning up real debounce timers in unit tests.
+    handler._schedule_reload = _noop_schedule_reload
+    return handler
+
+
+def test_delete_evicts_hash_entry() -> None:
+    handler = make_handler()
+    handler._file_hashes["/ext/dist/old-chunk.abc123.js"] = "digest"
+
+    handler.on_any_event(FileDeletedEvent("/ext/dist/old-chunk.abc123.js"))
+
+    assert "/ext/dist/old-chunk.abc123.js" not in handler._file_hashes
+
+
+def test_delete_of_untracked_path_is_a_noop() -> None:
+    handler = make_handler()
+
+    handler.on_any_event(FileDeletedEvent("/ext/dist/never-seen.js"))
+
+    assert handler._file_hashes == {}
+
+
+def test_move_out_of_dist_evicts_source_hash_entry() -> None:
+    handler = make_handler()
+    handler._file_hashes["/ext/dist/chunk.js"] = "digest"
+
+    handler.on_any_event(FileMovedEvent("/ext/dist/chunk.js", "/ext/tmp/chunk.js"))
+
+    assert "/ext/dist/chunk.js" not in handler._file_hashes