refactor(source-control): read the babysit loop keys from docs/conventions/source-control.yaml #9726

Parent

Refs #5906

Depends on

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

Outcome

The babysit_loop_* keys (stop_mode, tier, merge, grace_window_minutes) resolve from
docs/conventions/source-control.yaml for the local babysit loop and for babysit's remote read of a target
repository, with .claude/source-control.md 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.
• ADR 0064 Decision 9: a remote reader keeps its own fetch from the default branch through the contents API.

Key interfaces

• plugins/source-control/skills/babysit-prs/scripts/babysit_repo_config.py and its fake, the babysit-loop
  operator-options.mjs, the babysit eval scaffolds, scripts/promotion-evidence-e2e.test.mjs.

Done when

• docs/conventions/source-control.yaml holds the four babysit_loop_* values and scripts/check-convention-yaml.sh --check exits 0.
• scripts/run-test-file.sh plugins/source-control/skills/babysit-prs/scripts/tests/test_babysit_repo_config.py exits 0 with cases for: a remote YAML value wins, a remote repo with only the old file still resolves, neither file yields the defaults.
• scripts/run-test-file.sh scripts/promotion-evidence-e2e.test.mjs 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

• Deleting .claude/source-control.md.