ripr PR lane

ripr is the repository's static mutation-exposure lane. It answers the PR-time question from the product contract:

For the behavior changed in this diff, do the current tests appear to contain a discriminator that would notice if that behavior were wrong?

This lane shifts mutation-shaped signal left. It looks for weak oracle exposure statically before the repository spends runtime mutation budget.

Claims

ripr may report conservative static exposure classifications:

• exposed
• weakly_exposed
• reachable_unrevealed
• no_static_path
• infection_unknown
• propagation_unknown
• static_unknown

It must not claim runtime mutation outcomes, proof of correctness, or general test adequacy. Runtime mutation remains a separate backstop for selected risk surfaces.

Default placement

The intended PR lane is advisory by default:

Default PR:   static mutation-exposure analysis for changed production Rust
Risk PR:      static analysis plus targeted runtime mutation when risk pays
Nightly/main: broader runtime mutation calibration and trend receipts
Release:      readiness receipts that include targeted runtime evidence

Soft gating is allowed only after calibration. The current soft-gate doctrine is recorded in ripr-soft-gate.md and policy/ripr-soft-gate.toml.

Artifacts

The canonical PR packet should stay small and reviewable:

target/ripr/pr/
  pr-summary.md
  repo-exposure.json
  review.md
  agent-packet.json
  first-useful-action.md
  first-useful-action.json

Large repository scans are build-heavy in this repository. Prefer summary receipts, generated ledgers, and scoped reports for ordinary PRs. Run at most one intentional full refresh at a time and remove ad-hoc large JSON outputs after inspection.

Relationship to other lanes

Lane	Role
ripr	Static mutation-exposure signal for changed behavior.
cargo-mutants	Runtime mutation backstop where risk justifies cost.
Coverage / Codecov	Execution-surface telemetry; it does not establish discriminating oracles.
Focused tests	Local runtime evidence for the discriminator or behavior under review.

See also

• ripr-mutation-boundary.md — detailed language and mutation boundary.
• test-evidence-lanes.md — lane split across static, runtime, coverage, and release evidence.
• cost-and-verification-policy.md — CI economics doctrine.
• lem-budgeting.md — LEM planning unit and budget bands.