Clear the SSE event log on every worker start, including Retry failed.

Resume reused the previous pipeline_complete, so the UI closed the stream and showed no live log while U19 was still reviewing.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_event_bridge.py

@@ -0,0 +1,24 @@
+"""GCS event log: a new run must not replay a prior pipeline_complete."""
+
+from backend.services.event_bridge import GCSEventBroker
+
+
+def test_clear_history_wipes_terminal_events(tmp_path):
+    from backend.services.storage import LocalStorageBackend
+
+    storage = LocalStorageBackend(tmp_path)
+    broker = GCSEventBroker(storage, "local")
+    broker.publish("p1", "step_update", {"stage": "validation"})
+    broker.publish("p1", "pipeline_complete", {"summary": {}})
+
+    prefix = "users/local/projects/p1/events/"
+    assert len(storage.list_prefix(prefix)) == 2
+
+    broker.clear_history("p1")
+    assert storage.list_prefix(prefix) == []
+
+    broker.publish("p1", "step_update", {"stage": "bom_parse"})
+    keys = storage.list_prefix(prefix)
+    assert len(keys) == 1
+    assert keys[0].endswith("0000000000.json")
+    assert storage.read_json(keys[0])["event"] == "step_update"