Architectural review of the refactorer's postHeights index work. Extract a
shared assemblePostPage helper and a ListUseCase base class to remove DRY
duplication in the post-list use cases. Build the gherkin-mutator runner
adapter for psf-memo-db and psf-memo-indexer. Add boundary and tie-break
tests to kill all surviving language mutations across the changed files
(post-query, pagination, list use cases, indexer post handler).
Mutation: all changed source files fully killed. DRY: clean. CRAP <= 6.
Soft Gherkin acceptance mutation documented survivors (see review report).
By architect.
