# V2 Rust Build Time Regression Tracking

`V2/ue/Tools/compare-v2-rust-build-times.py` compares crate timing evidence from
the latest Rust compile-check against the accepted baseline. Evidence uses the
`v2.rust.buildTimeMetrics.v1` schema and is keyed by crate, target triple, and
profile.

The threshold is intentionally strict: any crate whose `durationSeconds`
increases by more than 10 percent is reported as a regression and the comparator
exits non-zero. Exactly 10 percent is allowed; anything above 10 percent blocks
the merge gate.

`run-v2-rust-premerge-validation.py` emits build time metrics from every
fail-fast Cargo command it runs, so pre-merge validation can publish current
timing evidence. Horde stores the accepted baseline at
`$(ArchiveRoot)/Rust/build-time-baseline.json`, writes current timing evidence
to `$(ArchiveRoot)/Rust/build-time-current.json`, and publishes
`$(ArchiveRoot)/Rust/build-time-regression-report.json`.

The required gates are `rust-build-time-report-generated`,
`rust-build-time-max-regression`, and `rust-build-time-regression-count`.