perf(api-service): reduce DB round-trips for inbox mark-seen

[cursor]

Context

APM data for the production US API over the last day showed the inbox “mark notifications as seen” web transaction as the slowest among high-volume routes, with database time as the dominant contributor and external time present but secondary. Error rate for that route was negligible relative to other endpoints, so the change targets latency, not correctness.

Root cause

The handler ultimately goes through MessageRepository.updateMessagesStatus, which:

1. Loads all matching document _ids for the filter.
2. For each batch of IDs, runs a primary updateMany-equivalent for the status fields, then a second conditional update for firstSeenDate when marking as seen.

With the previous batch size, a single request that touched many messages issued many sequential database round-trips (two writes per batch). The inbox use case also split explicit ID updates into small batches, which multiplied the preliminary ID find work.

What we changed

• MessageRepository: Use a larger ID chunk for status updates and, for the “mark as seen” path, send the paired updates as one ordered bulkWrite per chunk (still honoring the prior write concern). This preserves behavior (including firstSeenDate backfill) while cutting round-trips.
• BaseRepository.bulkWrite: Allow optional writeConcern / session so repositories can pass through Mongo options without touching _model directly.
• MarkNotificationsAsSeen: Increase the per-repository batch size when updating by notification IDs so fewer full find+update cycles run for large ID lists.

Risk / review notes

• Ordered bulkWrite keeps the main status update before the firstSeenDate conditional update within each chunk.
• Chunk size is chosen to balance BSON limits on $in queries vs fewer round-trips.

Testing

• pnpm exec tsc -p libs/dal/tsconfig.json --noEmit
• API unit tests could not be run in this environment because the test script sets NODE_OPTIONS=--no-experimental-strip-types, which Node v20 rejects.

  

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