Use the existing type index for event context queries

[ymichael]

Human comments

What was wrong

Bounded event-type queries in listStoredEventRows could use the thread/sequence index and filter by type, despite an existing thread/type/sequence index. A measured default timeline request executed six such context queries over 110,630 event rows. Even a query returning no rejected inputs took about 54 ms.

What changed

Select the existing events_thread_type_sequence_idx for typed queries, retaining the planner-selected path for unfiltered queries. Use the existing SQL field projection helper for Drizzle's indexed table expression. Ordering, bounds, type deduplication, limits and returned fields are preserved. No new index, migration, public API or daemon protocol change.

This is the first independent performance follow-up to #3817. It does not change conversation-context bounds or detail reconstruction.

How you verified

• Added the missing lower-bound case to the migrated SQLite query-plan regression. It fails before the change and passes after it.
• pnpm exec turbo run test typecheck --filter=@bb/db: 577 tests and typecheck pass, including event query ordering/bounds behavior.
• Compared default HTTP route cold opens, cached opens and unchanged deltas for all 2,385 threads in a consistent read-only main-database snapshot: all payload hashes match before/after. One deleted-thread 404 is unchanged. One warmup and three measured rounds per thread; nine initially flagged cold requests were rechecked with nine samples, followed by a reverse-order 15-sample confirmation for the remaining flag. No cold regression remained above both 10% and 5 ms.
• The slow context-heavy request fell from 456 ms to 118 ms in the census and 448 ms to 100 ms in the final confirmation. This includes route execution, serialization and response parsing, but excludes network/browser time; cold clears application caches, not disk caches. The broad census ran versions sequentially and the host was shared, so small distribution changes are not claimed as stable speedups.

AGENT GENERATED