fix(knowledge): read the projection-filled probe off the partial index instead of a sequential scan

[waleedlatif1]

Summary

• The search's "is this projection filled yet" probe was SELECT EXISTS (SELECT 1 FROM <projection> WHERE acl IS NULL). PostgreSQL drops the order and limit inside an EXISTS, and while most rows are still unfilled the planner expects a sequential scan to meet one immediately, so it never picks the partial acl IS NULL index. When the unfilled rows sit past the filled ones, that sequential scan walks the whole projection on every miss of the one-minute memo
• Because the probe runs under the search budget, ahead of the keyword ranking, it consumed the entire keyword leg on every member search of a large index and the leg returned nothing; the repeated full scans also kept the projection and its ranking index out of cache for everyone else
• The probe now asks for the last unfilled row by id (ORDER BY id DESC LIMIT 1). That shape can only be served by the partial index, so the read is a handful of pages regardless of how many rows remain (the fill advances from the front of each range, so the last entry is also the one it reaches last)
• The backfill's own end-of-chain probe (same EXISTS, joined to document) takes the same shape
• Measured on a production-sized index: the sequential-scan form ran past the search budget; the index form completes in single-digit milliseconds

Type of Change

• Bug fix

Testing

• Unit test pins the probe's rendered shape and fails against the previous EXISTS form
• bun run lint, check:audits (47 audits), docs-manifest:check, type-check pass

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 22, 2026 4:36pm UTC

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with the performance fix consistently applied and covered by focused regression tests.

Summary

This PR replaces sequential-scan-prone EXISTS checks with ordered, single-row probes that can use the partial unfilled-row index.

• Updates both the search-time projection readiness probe and the backfill completion probe.
• Preserves the backfill probe’s document join so orphaned projection rows do not block completion.
• Adds focused SQL-shape coverage for both probes, including the previously requested backfill assertions.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  Search[Knowledge search or backfill] --> Probe[Ordered unfilled-row probe]
  Probe --> Index[Partial ACL-null index]
  Index --> Found{Unfilled row found?}
  Found -->|Yes| Pending[Projection remains pending]
  Found -->|No| Ready[Projection is filled]

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[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

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[waleedlatif1]

@greptile

[waleedlatif1]

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[cubic-dev-ai]

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[cubic-dev-ai]

No issues found across 4 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

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