fix(lint): exempt ERB-templated Rails fixtures from yamllint

[bryanfawcett]

ERB templates are not YAML documents

campfire's test/fixtures/*.yml are ERB templates. users.yml opens with

<% password_digest = BCrypt::Password.create("secret123456") %>

and only becomes valid YAML after Rails renders it, so yamllint reports a hard syntax error and always will. There is no version of that file that is both a working fixture and parseable YAML. Seven files in that repo are ERB-templated YAML; the rest only parse because their ERB happens to sit inside quoted scalars — luck, not correctness.

The ActionText fixtures alongside them are HTML blobs that tests assert on byte-for-byte, so rewrapping their 300-char lines would be a test change disguised as a formatting change.

Same class as the lockfile exemption: content that is generated or templated rather than authored. This recurs in every Rails repo, and the narrower rule — skip any YAML containing <% — cannot be expressed in yamllint's path-based ignore.

Plus the worst hazard found so far, documented

A file with a .md extension that is not Markdown gets silently corrupted. mzizi-registry ships components/registry/n8-assurance/accessibility-audit.md, which is SQL, installed into consumers as documentation. Its /* … */ banner parses as Markdown emphasis, so prettier --write rewrites /* → /_ — turning a shipped artifact into invalid SQL and then passing the gate.

Unlike every other trap recorded here, this one does not fail loudly. It changes your file and goes green. Now in ADOPTING-LINT.md with the fix (wrap the body in a fenced code block — byte-for-byte unchanged, satisfies both tools, renders as code).

Unblocks nyuchi/campfire#1.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com