rvf: ingest accepts conflicting value types for one field id, failing later at snapshot time

Flagged consistently across three rounds of the ADR-280 review, out of scope each time.

ingest_batch_with_metadata accepts the same field id with different value types across records. A full snapshot covering both cannot be encoded, so the store acknowledges writes that only fail later — when a snapshot happens to materialize. That is an accepted-then-fails-later shape: the caller gets Ok, and the failure surfaces at an unrelated later commit.

(This was actually useful during review as a deterministic fault injector for testing rollback paths, which is how it kept coming up.)

Fix direction: reject the conflicting type at ingest time, so the error lands on the call that caused it.

🤖 Generated with claude-flow

Start at the ingest_batch_with_metadata entry point and trace how field ids and value types are validated before snapshot materialization. Reproduce the case with records that use different value types for one field id; done means the ingest call rejects the conflict instead of acknowledging it and failing later during a snapshot.