Fixes#195.
When ChromaDB returns no documents (empty palace, or wing/room filter
that excludes everything), it returns the shape:
{"documents": [], "metadatas": [], "distances": []}
Indexing `results["documents"][0]` blindly raises IndexError instead of
the expected 'no results' response. Affected: searcher.search(),
searcher.search_memories() (drawer + closet branches plus the
total_before_filter aggregate), and Layer3.search() / Layer3.search_raw().
Adds a tiny private helper `searcher._first_or_empty(results, key)` that
safely extracts the inner list, returning [] for any of: missing key,
empty outer list, [None], or [[]]. layers.py imports the same helper to
avoid duplicating the guard.
Tests: tests/test_empty_chromadb_results.py covers all observed shapes
plus a documentation-style test that pins the original IndexError so
future readers understand why the helper exists.
Arnold Wender
6a73eb2e20