refactor(guardrails): resolve the commit convention from docs/conventions/source-control.yaml #9727

Parent

Refs #5906

Depends on

• refactor(source-control): read the commit and PR convention keys from docs/conventions/source-control.yaml #9725

Outcome

The commit-subject convention that guardrails enforces (the commit-msg hook, block-convention-violation,
block-noncanonical-commit) resolves from docs/conventions/source-control.yaml. The folder-form
docs/conventions/source-control/commit-convention.yml moves into keys of that file. The old
.claude/source-control.md and the folder form are read only when the YAML lacks the key, for one release.

Decisions

• ADR 0064 Decision 1: a plugin's team settings live in one docs/conventions/<concern>.yaml, validated by a
  JSON Schema at plugins/<plugin>/schemas/<concern>.schema.json (Decision 6), checked in CI by
  scripts/check-convention-yaml.sh (Decision 7). Script readers use the shared reader lib/parse-concern-value.sh.
• ADR 0075: layers are plugin default < userConfig < team <home>/<concern>.yaml < personal
  <home>/<concern>.local.<ext>; every resolver reports the layer that supplied each value.
• Migrate per-skill .claude config files to userConfig, one conventions doc, or the cascade (ADR 0018) #5906 (comment 2026-10-04): each reader keeps reading the old file for one release when the new file is
  absent, and this repository keeps its old file until the cleanup slice.
• The convention is a policy floor read from the default branch (ADR 0064 Decision 5): the team layer wins.
• The resolver's single source is lib/resolve-convention-pattern.sh; plugin copies are regenerated with
  scripts/sync-shared-copies.sh.

Key interfaces

• lib/resolve-convention-pattern.sh and its copies, plugins/guardrails/git-hooks/commit-msg-convention.sh,
  plugins/guardrails/hooks/block-convention-violation.sh, plugins/guardrails/hooks/block-noncanonical-commit.sh,
  docs/conventions/commit-convention.

Done when

• docs/conventions/source-control/commit-convention.yml is gone and its values are in docs/conventions/source-control.yaml; scripts/check-convention-yaml.sh --check exits 0.
• scripts/run-test-file.sh lib/resolve-convention-pattern.test.sh exits 0 with cases for: YAML wins, folder form read when the YAML lacks the key, old file read when both lack it.
• scripts/run-test-file.sh exits 0 on plugins/guardrails/hooks/block-convention-violation.test.sh, plugins/guardrails/hooks/block-noncanonical-commit.test.sh and plugins/guardrails/git-hooks/commit-msg-convention.test.sh.
• scripts/sync-shared-copies.sh --check exits 0.
• The PR body lists each migrated key with its new home and schema.
• scripts/check-changelog-fragments.sh --check-required origin/main exits 0.

Out of scope

• The user-private commit convention layer (fix(guardrails): harden the commit-msg hook and add a config-hook install lane #5948).
• Reinstalling installed git hooks and deleting the old file (later slices under Migrate per-skill .claude config files to userConfig, one conventions doc, or the cascade (ADR 0018) #5906).