When a lane reset fails to rewrite the recreated collection, the recovery path
re-adds the preserved rows. It read the embeddings with
`preserved.get("embeddings") or []` and gated the loop with
`if ids and docs and old_embeddings:`. chromadb returns embeddings as a numpy
ndarray, whose truth value is ambiguous, so both expressions raise ValueError
inside the except block — the restore is abandoned and every preserved row is
lost (the collection was already deleted), exactly when the code is trying to
avoid data loss.
Use an explicit `is None` check and `len(...)`, and convert ndarray batches to
lists before re-adding.
Adds tests/test_embedding_lane_ndarray_restore.py (preserved embeddings come
back as np.ndarray); existing test_embedding_lanes.py still passes.
Mazen Tamer Salah