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.