consumeMetadata() was looping ALL notes in cache (O(N)) to find notes
by the author whose metadata changed. With hundreds of cached notes,
this caused lag on every metadata event.
Added notesByAuthor index (ConcurrentHashMap<HexKey, MutableSet<Note>>)
populated at loadEvent time. consumeMetadata now looks up notes by
author in O(1) instead of scanning the entire cache.
Before: ~500 notes × per metadata event = lag
After: ~3 notes per author × per metadata event = instant
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
nrobi144
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