chore(ci): read the post-merge mutation lane's config from docs/conventions/mutation-testing.yaml #12289

Parent

Refs #5906

Blocked by

• the code-metrics and mutation-testing plugin slice (linked as this issue's blocker)

Outcome

This repository's mutation-testing team settings live in docs/conventions/mutation-testing.yaml, and the post-merge
mutation lane's files name that file instead of .claude/mutation-testing.md:

• .github/scripts/post-merge-test-mutation/report.test.mjs:304,313 reads the mutate globs from the YAML;
• .github/scripts/post-merge-test-mutation/prompt.md:5 names the YAML as the team layer;
• the comment at .github/workflows/post-merge-select-mutation-range.yml:10 names the YAML.

The YAML's mutate list excludes docs/conventions/**, as the old file's excludes .claude/**, so that
report.test.mjs requires the audit job to deny Edit(./docs/conventions/**) and the lane's model cannot edit its
config. That requires two workflow edits: the deny in the audit job's denied list in
.github/workflows/post-merge-test-mutation.yml, and "!docs/conventions/**" in the paths filter of
.github/workflows/post-merge-select-mutation-range.yml, which must equal mutate.

Once the mutation-testing release carrying the code-metrics and mutation-testing plugin slice (linked as this issue's blocker) has shipped, .claude/mutation-testing.md is deleted and the
plugin's one-release read of it is dropped (#5906 body, Scope 3: a compatibility read of the old file for one release).

Host-run: the issue lane cannot push .github/workflows/, and report.test.mjs runs under node.

Key interfaces

• .claude/mutation-testing.md, whose mutate list excludes .claude/** because the lane's model may not edit its
  config; report.test.mjs checks that every excluded glob is a denied Edit rule of the audit job and that the
  gate's paths filter equals mutate.
• .github/workflows/post-merge-select-mutation-range.yml (paths) and .github/workflows/post-merge-test-mutation.yml
  (the audit job's denied list).
• plugins/mutation-testing/skills/setup/SKILL.md, the config merge model the code-metrics and mutation-testing plugin slice (linked as this issue's blocker) changes.

Done when

• docs/conventions/mutation-testing.yaml carries every key of .claude/mutation-testing.md, its mutate list also excludes docs/conventions/**, and scripts/check-convention-yaml.sh --check exits 0.
• node --test .github/scripts/post-merge-test-mutation/report.test.mjs exits 0, with both config reads on docs/conventions/mutation-testing.yaml.
• git grep -n "\.claude/mutation-testing\.md" -- .github prints nothing.
• plugins/mutation-testing/CHANGELOG.md shows a released version after the one carrying the code-metrics and mutation-testing plugin slice (linked as this issue's blocker) (grep -n on the version heading prints it).
• git ls-tree --name-only HEAD .claude/ does not list mutation-testing.md.
• git grep -nE "\.claude/mutation-testing\.md" -- plugins docs/contracts ":!*CHANGELOG.md" prints only setup lines that report or move the retired file, and lines that name ~/.claude/mutation-testing.md as never read.
• scripts/check-changelog-fragments.sh --check-required origin/main exits 0.

Out of scope

• The lane's personal overlay .claude/mutation-testing.local.md, written at
  .github/workflows/post-merge-test-mutation.yml:188 (ADR 0075 fix 8).
• The arid-node record .claude/mutation-testing-arid.md.

Posted by the issue-triage session. This was generated by AI.