react-v1.15.2

Fixes

• Comment selection feedback — Superseded SELECTED events drop to prevent racing with rendered highlights. Pending events defer and cancel.
• Metadata anchor validation — Overlapping anchored-metadata ranges are rejected (INVALID_TARGET) instead of creating duplicates. Selection normalizes on remove to prevent stale carets.
• Custom XML synchronization — Metadata and customXml writes route through the parts mutation layer so partChanged fires and part-sync publishes correctly across clients.
• Custom XML tombstone handling — Tombstones record for deleted custom XML parts on remote deletes and late-join. Stale tombstones clear when parts are recreated or rehydrated.
• Bibliography cache invalidation — Converter caches invalidate when custom XML paths are written or hydrated, preventing export from rebuilding parts with stale cached content.
• Metadata payload validation — Payload serializability validates during attach preview before document mutation, preventing orphaned content controls on serialization failure.