Infrastructure-failure ratio — jobs failed for platform reasons as a share of all jobs — is the single signal that decides whether engineers trust a red build. It is bounded at ≤ 0.5% weekly and alerts at 1.0% hourly.
Flake rate is measured but deliberately not bounded. The platform's obligation is detection; fixing a flaky test belongs to the team that owns it.
Trust misclassification is a correctness signal on admission and is a Sev-1 at any non-zero value.
Deliberate gaps
No cost signal at admission or promotion: neither consumes attributable compute, and inventing an allocation would make the cost-per-job-minute figure less honest.
No security signal at the queue: a queued job holds no credential and touches no tenant data.
Assumptions
All-in cost target ≤ $0.011 per job-minute at p50 utilisation; elevated infra-failure ratio detected within 5 minutes.
