feat(covgate): report build-cache pre-warm duration#35
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The pre-warm pass before the parallel coverage runs was invisible: it is
excluded from "Total time" (which times only the parallel phase) and emitted
no output, so its cost could not be observed or compared run-to-run.
Announce the pass ("Pre-warming build cache (N packages)...") and report its
wall time on completion ("Pre-warm complete in X"). Extract the warm logic
into prewarmCache so run() stays within the function-length limit.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Make the covgate build-cache pre-warm pass observable: announce it and report its wall time.
Why
The pre-warm pass (added in #34) is a large slice of a covgate run but was invisible: it's deliberately excluded from "Total time" (which times only the parallel coverage phase) and emitted no output. So you couldn't see how long it took, or tell whether it was helping — which is exactly the situation that prompted this: a downstream run where the pre-warm appeared to underperform, with no way to confirm from the logs.
Change
Pre-warming build cache (N packages)...before it andPre-warm complete in Xafter, to the same writer as the rest of the output.prewarmCache(...)sorun()stays within the repo's function-length limit.No behavior change to coverage measurement, thresholds, exclude handling, gating (
parallelism > 1 && len(pkgs) > 1), or "Total time" — purely additive observability.Tests
TestRun_Prewarm_InvokedOnce_WhenParallelAndMultiPkgto assert both new lines appear.TestRun_Prewarm_Skipped_WhenSinglePackageOrSerialto assert they do not appear when the pass is gated off.Context
This is the diagnostic prerequisite for an observed regression: when a downstream repo (backend) switched from a CI-side pre-warm step to covgate's internal self-warm, the combined warm + coverage time looked worse than the external step. With this output we can measure the pre-warm and coverage phases separately on a clean run and confirm the cause before changing the warm logic.
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