Captures per-span / per-RPC / per-job timings from Prometheus after the
workload run and diffs them against a committed baseline. Regression
requires breaching both a percentage and an absolute bound, tolerating
small-value noise. When the baseline is a placeholder, the comparator
emits the captured JSON in the exact schema for one-time paste into
baselines/baseline-timings.json, and the CI Step Summary surfaces that
block for the reviewer.
Scope: gate only — automated baseline persistence, benchmark.sh
PromQL migration, and the historical trend dashboard remain follow-ups.
