Capture the actual regression
Choose the boundary with Verify This. Use the TDD workflow for a focused runtime regression. Use real positive and negative consumers for a compiler or generated-API contract.
For Hspec, run python3 .agents/skills/regression-evidence/scripts/evidence.py runtime --repo <root> --input <affected-source> --test <exact-example> --expect fail --failure <independent-assertion-text> -- <test-command>. Repeat with --expect pass after the fix. The command must run the affected implementation. Expected failure needs one matching assertion failure, a nonempty selection and no setup or compiler failure.
For compiler contracts, run python3 .agents/skills/regression-evidence/scripts/evidence.py compiler --repo <root> --positive <accept.hs> --negative <reject.hs> --diagnostic <expected-regex> -- <ghc-flags>. The helper first requires a successful positive compilation, then a failure in the negative fixture with the expected diagnostic. Add relevant framework sources, generated declarations and build configuration through repeated --input arguments. Compiler rejection proves that compiler contract, not runtime behavior.
Runtime claims require demanded values, executed Tasks or decisions, and the promised observable result. Select independent expectations and meaningful properties. A copied implementation, assertion on a fixture alone, setup failure or arbitrary compiler exit is insufficient evidence.
The helper retains argument arrays, selected source snapshots, hashes, logs and observed outcomes under .agents-state/regression-evidence/. It rejects changes to the selected inputs during execution. This binds the captured run to those inputs. It does not establish complete dependency coverage or authenticate a hand-edited receipt. State the tested revision, dirty state, inputs and limitations in the result.