Runtime verification found the deterministic generator merges the prior
served narrative, so a replaced (semantic) narrative would linger after
rollback. Store the displaced deterministic narrative in the shadow report
(persisted via shadow_json) and merge that instead when the prior summary
source is semantic_replace.
Unseal SEMANTIC_SUMMARY_REPLACE under explicit user authorization with a
defense-in-depth session allowlist (SEMANTIC_SUMMARY_REPLACE_SESSIONS):
swap happens only for allowlisted sessions after result digests and served
watermark validation, bounded narrative size; facts/counts stay deterministic
and the daily digest stays advisory. Master flag alone replaces nothing.