ADR 0014: Experiment-scoped file embedding cache (remove pipeline_signature)

Date: 2026-01-13

Context: File-level embeddings are reused across commits and must remain consistent with locked experiment behaviour settings. Decision: Scope MapElitesFileEmbeddingCache by experiment_id and key rows by (experiment_id, blob_sha); store embedding_model and dimensions for validation; remove pipeline_signature. Consequences: File embeddings cannot be reused across experiments with different snapshots; cache keys are simpler and aligned with experiment config locking. Upgrading requires resetting the development database schema (Loreley does not ship migrations).