Reason: SentenceTransformer.encode() in sentence-transformers 5.5.1 does
not accept return_dense / return_sparse kwargs. Those belong to the
FlagEmbedding.BGEM3FlagModel API, which is not in our dependency set.
Dense encoding works fine via the vanilla encode() call (shape (N, 1024),
float32). Sparse / lexical_weights requires either:
(a) adding FlagEmbedding as a dependency, or
(b) using sentence_transformers.SparseEncoder with a SPLADE checkpoint, or
(c) driving the underlying transformers model and sparse head manually.
Branch retained as documentation per docs/loops/spike-gate.md.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
