fix(rag): convert RAGChunk to dict in _rag_search_result to match type contract

The RAG engine's search() returns List[RAGChunk] (dataclass instances),
but _rag_search_result's return type is Result[list[Metadata]] (a list
of dicts). The previous code returned the RAGChunks as-is, then the
caller in _handle_request_event did chunk["metadata"] (dict access
on a dataclass) which raised TypeError. The exception was silently
swallowed by the submit_io worker, leaving ai_status stuck at
sending... for the full 50-second test poll before failing.

Two surgical changes:
1. _rag_search_result: convert RAGChunk to dict via to_dict() (with a
   hasattr guard for tests that return dicts directly). Matches the
   function's documented return type.
2. _handle_request_event: use isinstance guards + dict.get() on the
   chunk fields. Defensive against the type mismatch and matches the
   dict contract.

The test fix (unique collection name + workspace-targeted cleanup)
is the test-side complement that prevents the dim-mismatch path from
being hit in batched runs.

Verified: 4 consecutive PASS runs of test_rag_phase4_final_verify in
isolation (7-8s each). 25/26 RAG tests pass; the one remaining
failure (test_rag_collection_dim_mismatch_recreates_collection) is a
pre-existing regression from commit 24e93a75 which changed the dim
check from delete_collection to shutil.rmtree without updating the
test mock setup. Out of scope for this fix.

src/app_controller.py

@@ -3501,14 +3501,17 @@ class AppController:
 
  def _rag_search_result(self, user_msg: str) -> "Result[list[Metadata]]":
   """Per-event handler (Phase 6 Group 6.6): RAG search via the engine.
-  Returns Result[List[RAGChunk]]. On failure: any engine/SDK exception
-  -> ErrorInfo(original=e). Caller (`_handle_request_event`) appends
+  Returns Result[List[Metadata]] (list of dicts per the function's
+  type annotation; the engine's search() returns List[RAGChunk]
+  dataclasses which are converted via to_dict() here so the caller
+  in `_handle_request_event` can use dict-style access). On failure:
+  any engine/SDK exception -> ErrorInfo(original=e). Caller appends
   to `self._last_request_errors` for sub-track 4 GUI display."""
   if not (self.rag_engine and self.rag_config and self.rag_config.enabled):
    return Result(data=[])
   try:
    chunks = self.rag_engine.search(user_msg)
-   return Result(data=list(chunks) if chunks else [])
+   return Result(data=[c.to_dict() if hasattr(c, "to_dict") and not isinstance(c, dict) else (c if isinstance(c, dict) else Metadata()) for c in chunks])
   except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, RuntimeError) as e:
    return Result(data=[], errors=[ErrorInfo(
     kind=ErrorKind.NETWORK,
@@ -4171,18 +4174,18 @@ class AppController:
   [C: tests/test_live_gui_integration_v2.py:test_user_request_error_handling, tests/test_live_gui_integration_v2.py:test_user_request_integration_flow, tests/test_rag_integration.py:test_rag_integration]
   """
   self.ai_status = 'sending...'
-  
+
   user_msg = event.prompt
-  
+
   # 1. RAG Retrieval (Enrich prompt before logging to history)
   if self.rag_engine and self.rag_config and self.rag_config.enabled:
    rag_result = self._rag_search_result(user_msg)
    if rag_result.ok and rag_result.data:
     context_block = "## Retrieved Context\n\n"
     for i, chunk in enumerate(rag_result.data):
-     chunk_meta = chunk["metadata"] if "metadata" in chunk else {}
-     path = chunk_meta["path"] if "path" in chunk_meta else "unknown"
-     doc = chunk["document"] if "document" in chunk else ""
+     chunk_meta = chunk.get("metadata", {}) if isinstance(chunk, dict) else {}
+     path = chunk_meta.get("path", "unknown") if isinstance(chunk_meta, dict) else "unknown"
+     doc = chunk.get("document", "") if isinstance(chunk, dict) else ""
      context_block += f"### Chunk {i+1} (Source: {path})\n{doc}\n\n"
     user_msg = context_block + user_msg
    elif not rag_result.ok: