ADR 0013: Remove filter_signature and prompt_signature from experiment-scoped caches

Date: 2026-01-09

Context: Loreley assumes env-only settings are stable for the lifetime of a database. Some caches still include extra signature dimensions (filter_signature, prompt_signature) that only exist to support dynamic changes.

Decision: Remove filter_signature from repo-state commit aggregates and key MapElitesRepoStateAggregate only by (experiment_id, commit_hash).

Decision: Remove prompt_signature from trajectory chunk summaries and key CommitChunkSummary only by (experiment_id, start_commit_hash, end_commit_hash, block_size).

Consequences: Aggregate and summary caches become simpler and aligned with the locked experiment settings model. Upgrading requires resetting the development database schema (Loreley does not ship migrations).