test(rag): wait for files setter before triggering RAG sync

The set_value('files', ...) call is async (push_event -> pending_gui_tasks
-> render loop). The RAG setters (rag_enabled, rag_source, rag_emb_provider)
are also async and each triggers a RAG sync via submit_io. The syncs and
the files setter are NOT ordered: the sync may fire before the files
setter is processed, in which case the sync sees self.files == [] and
skips the rebuild (RAG sync only triggers the rebuild if both
is_empty() AND self.files are truthy).

Fix: poll get_value('files') until the expected value is reflected,
guaranteeing the files setter is processed before the RAG setters
trigger their syncs. Belt-and-suspenders alongside the project-switch
fix from the previous commit.

The test was passing in 4d2a6666 because of timing; the project
switch added latency, so the race is now exposed.

tests/test_rag_phase4_final_verify.py

@@ -69,8 +69,18 @@ def test_phase4_final_verify(live_gui, live_gui_workspace):
 
  try:
   # 2. Configure project through Hook API
+  # set_value is async (push_event -> pending_gui_tasks -> render loop).
+  # Wait for the files setter to be processed before triggering the RAG
+  # sync, otherwise the sync sees self.files == [] and skips the rebuild
+  # (RAG sync only triggers the rebuild if both is_empty() AND self.files
+  # are truthy). The test was passing in 4d2a6666 because of timing;
+  # the project switch added latency, so the race is now exposed.
   client.set_value('rag_collection_name', _collection_name)
   client.set_value('files', ['final_test_1.txt', 'final_test_2.py'])
+  for _ in range(50):
+   if client.get_value('files') == ['final_test_1.txt', 'final_test_2.py']:
+    break
+   time.sleep(0.1)
   client.set_value('rag_enabled', True)
   client.set_value('rag_source', 'chroma')
   client.set_value('rag_emb_provider', 'local')