yamllint config is incompatible with Ruby/Psych-generated YAML files

[ineedjet]

Problem

The current baseline yamllint config has two rules that conflict with YAML files generated by Ruby's Psych (the standard Ruby YAML serializer used by Rails, RuboCop, i18n-tasks, etc.):

1. document-start: present: false — Psych always adds --- to the start of every document. This cannot be disabled via options in any Ruby version (including Ruby 4 / Psych 5.4).

2. indentation: indent-sequences: true (inherited from extends: default) — Psych always outputs block sequences at the same indentation level as the parent key (non-indented style). This also cannot be changed via options.

Psych output (always)

---
en:
  date:
    abbr_day_names:
    - Sun
    - Mon

What baseline yamllint requires

en:
  date:
    abbr_day_names:
      - Sun
      - Mon

Psych has no options to suppress --- or produce indented sequences — both behaviors are hardcoded in libyaml's C emitter.

Affected files in a typical Rails project

• config/locales/*.yml — generated/normalized by i18n-tasks
• .rubocop_todo.yml — generated by rubocop --auto-gen-config
• .rubocop.yml, .erb_lint.yml — blank lines between sections (separate issue, already fixed by removing blank lines)

Consequence

In a Rails project using baseline's yamllint linter, i18n-tasks health and yamllint are mutually exclusive:

• If locale files pass yamllint → i18n-tasks health fails ("data requires normalization")
• If i18n-tasks normalize is run → yamllint fails

Proposed solution

Support two yamllint profiles in baseline — one for Psych-generated files, one for human-written files:

config/yamllint/default.yml   # current rules, for human-written YAML
config/yamllint/psych.yml     # relaxed rules for Psych output

Or alternatively, support a project-level yamllint config override (e.g. .yamllint-baseline.yml that extends the baseline config), so projects can add their own ignore: patterns or rule overrides.

A minimal fix would be adding config/locales/ to the baseline ignore: block, since locale files are a universal Rails pattern.