Verify genuine Google music constraints and separate metadata cache revisions

crates/searchi-service/README.md

@@ -44,6 +44,7 @@ unchanged-vector reuse and production platform checks remain release gates.
 
 Exact artist/title constraints use the core's normalized structured probe keys
 before ANN limits and in the eligibility cache key. Metadata-only writes advance
-the corpus revision and dirty path so warmed readers cannot retain old eligibility.
+a separate durable metadata epoch so warmed readers cannot retain old eligibility.
+They do not change source-corpus revisions during the indexer's own probe publication.
 Empty metadata-only hybrid requests use core results without model inference.
 These explicit constraints do not establish abstention for free-form topic queries.