`rag_cite` and `analysis_cite` accepted only a non-empty `chunk_ids`, so a model with
nothing to cite could comply only by staying silent — indistinguishable from
forgetting. An empty list is now a valid answer to "what grounds this?", recorded as a
declaration with no refs, which derives `ungrounded` rather than leaving the question
undeclared. Citing again cannot narrow it: an empty call after a grounded one leaves
it grounded.
The instructions lose their carve-outs. Refusing for lack of information no longer
exempts the call, and a corpus-level computation cites an empty list instead of
skipping.
