Optimize streaming message projection path

[juliusmarminge]

Summary

• replace full-thread message scans in the projection hot path with per-message lookup and SQL delta append
• add repository coverage for getByMessageId and streaming appendTextDelta
• keep the perf artifacts and result log updated in performance.md

Perf impact

• create-turn-spam-8x thread.create dispatch -> thread.created: 3.61ms / 58.38ms -> 2.38ms / 20.36ms
• create-turn-spam-8x thread.archive dispatch -> thread.archived: 5.71ms / 50.80ms -> 0.97ms / 16.53ms
• biggest win here is the control-plane tail: ack -> event for thread.create dropped from 56.95ms p95 to 19.22ms p95

Testing

• bun run --cwd apps/server test src/persistence/Layers/ProjectionThreadMessages.test.ts src/orchestration/Layers/ProjectionPipeline.test.ts
• bun run --cwd apps/server test:perf
• bun run fmt .
• bun run lint
• bun run typecheck

Stacked on the checkpoint-reactor PR.

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Note

Medium Risk
Changes the message projection persistence/write path and SQL upsert semantics for streaming updates, which could affect message text/attachment consistency if edge cases are missed. Scope is limited to projection read-model storage and is covered by added repository tests.

Overview
Optimizes the thread.message-sent projection hot path for streaming messages. Instead of scanning all messages in a thread to find the current one, the pipeline now either appends streaming text via a new SQL appendTextDelta operation or does a direct per-message lookup (getByMessageId) before a final upsert.

The thread message projection repository API is extended with getByMessageId and appendTextDelta, with new SQL queries to support single-row lookup and conflict-based delta concatenation while preserving existing createdAt/attachments. Tests are added to cover the new lookup and streaming-delta behavior (including attachment/createdAt preservation).

^{Written by Cursor Bugbot for commit 3bec3d2. This will update automatically on new commits. Configure here.}

Note

Optimize streaming message projection by appending text deltas instead of reconstructing full rows

• Streaming thread.message-sent events now call appendTextDelta on ProjectionThreadMessageRepository, concatenating incoming text onto existing rows via SQL COALESCE rather than upserting a full reconstruction.
• Non-streaming upserts now fetch the existing row via getByMessageId to preserve createdAt and retain prior attachments when the event omits them.
• Adds getByMessageId and appendTextDelta to the repository shape in ProjectionThreadMessages.ts with corresponding input schemas.
• Behavioral Change: streaming events no longer fall back to previously persisted attachments at the projection stage; attachments are only carried forward when explicitly present on the event.

^{Macroscope summarized 3bec3d2.}

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[macroscopeapp]

Approvability

Verdict: Approved

Performance optimization that refactors streaming message persistence from JavaScript-based text concatenation to database-level upserts. The change is self-contained to the projection pipeline, includes comprehensive tests, and the author is the primary owner of this code.

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