mutation

name	mutation
description	Triage and act on the weekly [mutation] rolling issue (mutation-testing run health)
disable-model-invocation	true
argument-hint	[issue number]

Act on the [mutation] rolling issue: classify each failing scope, fix the harness/implementation regression behind it, and prepare a pushed branch for the user to open the PR via /pr.

Authority (do not duplicate — read these):

• sdd/CI-OPERATIONS.md — the cross-guard handbook: where this guard sits in the scheduled/automated family and the durable-TODO principle it follows.
• .github/workflows/mutation.yml header — the two-outcome model and its non-goals (the run never fails on surviving mutants).
• scripts/mutation_report.py module docstring — outcome JSON shape, classification rules, and the partial-run-never-closes semantics.
• scripts/mutate_scopes.py — the scope manifest (targets, tests, containers).

The core rule this skill exists to enforce: the issue tracks run health, not mutants. A scope listed under Harness / implementation failures is a regression — the run itself broke — and is fixed like any bug (backlog item, failing test where applicable, fix, same commit). Surviving mutants are advisory test-coverage gaps: they never open the issue, never turn the run red, and are folded into a coverage-hardening pass, not patched ad hoc to silence a report.

GitHub reads via gh CLI; writes (PR) via the configured GitHub MCP server. Repo: haalfi/remote-store.

Steps

1. Locate the issue. If $ARGUMENTS is an issue number, use it. Otherwise find the single open rolling issue by title prefix: gh issue list --repo haalfi/remote-store --state open --search '[mutation] in:title'. None open → the run is healthy, nothing to do; stop and say so.

2. Parse the body. Extract the failing scopes with their reasons, any advisory survivor counts, and the Last run URL. The body is regenerated on every full run and auto-closes on a healthy run — never edit it.

3. Pull the failing legs' logs (load-bearing). From the run URL's id: gh run view <id> --repo haalfi/remote-store --json jobs, then for each failing mutate-<scope> job: gh run view --repo haalfi/remote-store --job <jobId> --log-failed. Classify the failure:

   • Baseline test failure — the scope's tests fail before mutation even starts. Fix the test/code regression first; mutation is a bystander.
   • Harness/tooling break — an import error, plugin INTERNALERROR, dependency/config change, or a timeout cascade (no tests ran). Fix the harness (mutate_scopes.py targets, the workflow's install step, or the plugin pin), not the tests.
   • (setup) pseudo-scope — the setup job died before listing scopes (e.g. an import chain reaching for a dep the bare runner lacks). Fix scripts/run_mutate.py / mutate_scopes.py imports or the workflow.

4. Reproduce locally before claiming a fix: hatch run mutate <scope> (containers per the scope's needs start via infra/docker-compose.yml). Per CLAUDE.md principle 6, see it fail, fix, see it pass.

5. Survivors (advisory). If the body or the run-summary table lists surviving mutants, do not treat them as part of this triage. Note them for a coverage-hardening pass; the per-scope detail is in the mutation-report-<scope> HTML artifacts.

6. Branch hygiene. Never on master; create a dedicated branch off origin/master, e.g. fix-mutation-<slug>.

7. Ship complete. Backlog item + trace per CLAUDE.md; CHANGELOG only if a user.* audience is touched (a pure harness fix is not).

8. Stop for the user to open the PR. Push the branch, report the per-scope diagnosis and fix, then stop — PR creation is user-initiated via /pr. Reference the rolling issue with Refs #<n> — never Closes: the workflow owns the issue lifecycle and closes it on the next healthy full run. To close promptly after merge, dispatch a full run: gh workflow run mutation.yml --repo haalfi/remote-store.

Rules

• A red mutation run is always a harness/implementation regression — pytest's exit code never reflects survivors. Treat it with bug-fix urgency.
• Never silence a scope (skip, filter, pardon) to make the issue close; fix the cause or escalate with the diagnosis.
• A single-scope dispatch can verify one fix but never closes the issue or rewrites its body (its findings land as comments); only a healthy full run closes it. Never close the rolling issue by hand.