perf(server): stop maintaining redundant projection indexes

[extoci]

Four projection indexes are strict prefixes of later ordering indexes. SQLite can use the longer indexes for the same lookups, but every projection write still maintained both B-trees.

Drop the redundant indexes in migration 55, after Orchestrator v2 migration 54, and keep the covering indexes that serve the existing read plans. The migration is safe to rerun and a focused test verifies both sides of that contract.

The benchmark used a 1.25 GB snapshot of a real T3 database and representative activity rows with approximately 3.9 KB payloads.

Benchmark	Before	After	Change
Insert 10,000 activity rows	580.8 ms	520.6 ms	10.4% faster
Read 1,000 activity rows	14.3 ms	13.8 ms	No regression
Database storage	—	5.48 MB reclaimed	Smaller

The representative read kept the same covering-index query plan after the migration.

Validation: the focused migration test runs through Orchestrator v2 migration 54 and the cleanup migration 55. The v2 server typecheck passes, and targeted lint and formatting pass. The copied-database benchmark exercised the same index drops before retargeting.

Model: GPT-5.6 Sol. Harness: Codex in T3 Code.

[macroscopeapp]

Approvability

Verdict: Approved at 5737d93

Macroscope's review found this PR approvable — This adds a one-time migration that removes four redundant SQLite indexes while retaining composite indexes with the same lookup prefixes. The change is narrowly scoped, preserves query semantics, and includes coverage for normal and preview upgrade paths.

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📥 Commits

Reviewing files that changed from the base of the PR and between 61b25b8 and 695a963.

📒 Files selected for processing (3)

• apps/server/src/persistence/Migrations.ts
• apps/server/src/persistence/Migrations/054_RemoveRedundantProjectionIndexes.test.ts
• apps/server/src/persistence/Migrations/054_RemoveRedundantProjectionIndexes.ts

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📝 Walkthrough

Walkthrough

Migration 054 removes four redundant projection indexes. The migration registry includes it for execution and manifest generation. An in-memory SQLite test verifies that the redundant indexes are absent and covering indexes remain.

Changes

Projection Index Cleanup

Layer / File(s)	Summary
Projection index removal apps/server/src/persistence/Migrations/054_RemoveRedundantProjectionIndexes.ts	Migration 054 uses SqlClient to execute four DROP INDEX IF EXISTS statements.
Migration registration and validation apps/server/src/persistence/Migrations.ts, apps/server/src/persistence/Migrations/054_RemoveRedundantProjectionIndexes.test.ts	The migration is imported and registered with ID 54. The SQLite test verifies the removed and retained indexes.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: stopping maintenance of redundant projection indexes.
Description check	✅ Passed	The description explains what changed, why it changed, the performance impact, migration safety, preserved indexes, and validation results. It does not use the template headings or include the checkli…

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[juliusmarminge]

Retarget against v2 pls. Would prefer not introducing more migrations on main cause numbers conflicts

Dismissing prior approval to re-evaluate 5aa2c9a

[macroscopeapp]

Macroscope has since reviewed this pull request. An earlier review was skipped by a cost limit; a review has now completed, so that notice no longer applies.

Dismissing prior approval to re-evaluate 5737d93