Measure real PR review performance

[pandemicsyn]

Summary

• add a repeatable npm run bench:pr-review command for immutable revisions in registered repositories
• measure backend cold/warm/local/fallback behavior and production-browser tree, thread, and first-patch readiness
• reconcile the frontend audit and PR performance plan with phases 1–5 that already shipped
• retain the original findings and document candidate fixes without changing production behavior

Real target

Measured open Kilo-Org/kilocode#12204 at a fixed head/base revision:

• 1,019 files, 45,053 additions, 23,744 deletions
• 47 review threads; two unresolved paths
• both target objects were absent before the first local request

Results

• cold local metadata: 4,978 ms, 295 kB, zero truncated files; misses the 3 second target
• warm backend: 311 ms file list and 643 ms sequential first patch
• production browser medians: 869 ms tree, 1,971 ms first patch, 2,183 ms threads
• production rendering remained healthy: 876 ms LCP, 0.0012 CLS, zero long tasks
• every browser sample started two review-thread requests as optimistic PR state settled to authoritative detail
• four concurrent local patches took 1,952 ms because each patch path recomputes full 1,019-file metadata
• GitHub fallback: 3,894 ms cold / 24 ms cached, 765 kB metadata, one truncated file

Discussion gate

This PR intentionally does not implement the measured production fixes. The plan now proposes, in order:

1. stabilize review-thread query identity while preserving explicit invalidation
2. reuse or single-flight immutable local metadata across patch reads
3. remeasure before delaying neighbor/unresolved prefetch or changing the cold-fetch target

Verification

• npm run bench:pr-review -- ... --samples 3
• npm run build:dashboard
• npm run check (84 files, 524 tests)
• npm run format:check
• standalone Oxlint and syntax checks for the new benchmark
• direct Chrome DevTools production trace
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Require loaded thread state before timing zero-thread PRs

If this benchmark is run against a PR with no review threads, the review header already renders 0/0 threads before the review-threads request resolves, so body.includes('/0') && body.includes('threads') can mark threadsVisibleMs at initial paint instead of endpoint/UI readiness. That makes zero-thread PR samples under-report the thread path the harness claims to measure; wait for a completed thread response or a loaded-state marker before accepting the 0 case.

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