Fix RAG remove_directory wiping the entire shared collection (#1660) (#1734)

Removing one RAG directory destroyed the whole shared ChromaDB collection
(all owners + base index) instead of just that directory's chunks. Shared
root cause: PersonalDocsManager.remove_directory called rebuild_index()
(delete_collection + recreate) then re-indexed only the remaining tracked
dirs (ownerless, never personal_dir). The targeted VectorRAG.remove_directory
that should have been used was itself broken (where={"source":{"$contains":dir}}
selects nothing on scalar metadata and would over-delete siblings), and the
dead do_manage_rag path fired a second unconditional rebuild.

- VectorRAG.remove_directory: select chunks in Python by a path-boundary match
  on the stored absolute `source` (dir or dir+os.sep), abspath-normalized.
  Keys on `source` (always written), never `owner` -- no migration.
- PersonalDocsManager.remove_directory: call the targeted remove instead of
  rebuild_index() + partial reindex.
- do_manage_rag (dead code): drop the second rebuild_index() (hygiene).
- rag_server.py add path: abspath so indexed `source` matches the remove.

No schema change. Prevents future wipes (does not recover already-wiped
vectors). Adds hermetic regression tests at three layers.

Fixes #1660

Co-authored-by: Ethan <23321960+0xLeathery@users.noreply.github.com>

src/ai_interaction.py

@@ -1232,9 +1232,11 @@ async def do_manage_rag(content: str, session_id: Optional[str] = None) -> Dict:
 
         try:
             if hasattr(_personal_docs_manager, 'remove_directory'):
+                # Performs a targeted per-directory delete (#1660). The previous
+                # unconditional _rag_manager.rebuild_index() here wiped the whole
+                # collection on every remove (even for untracked dirs) and has
+                # been removed.
                 _personal_docs_manager.remove_directory(directory)
-            if _rag_manager and hasattr(_rag_manager, 'rebuild_index'):
-                _rag_manager.rebuild_index()
             return {"action": "remove_directory", "directory": directory,
                     "results": f"Directory '{directory}' removed from RAG index"}
         except Exception as e: