Detects potential regression risks in a PR by cross-referencing lines the PR REMOVES against lines ADDED by recent labeled bug-fix PRs (`i/regression`, `t/bug`, `p/0`, `p/1`) touching the same files. Purely mechanical — no AI/LLM. Emits a CLEAN / OVERLAP / REVERT verdict plus structured findings. Triggers on: "does this PR revert a previous fix", "check PR for regression risk", "find regression risks in PR", "is this change reverting a bug fix". Do NOT use for: assessing ship-readiness of a release branch (use release-readiness), investigating CI failures (use azdo-build-investigator), or general code review (use code-review).