Validates commit messages against Conventional Commits + project-specific rules.

Pure functions — no git, no filesystem. The Mix task wraps this module to read a COMMIT_EDITMSG file and produce CLI output.

Rules applied

• Format: <type>(<scope>)?(!)?: <subject>
• Type: must be in bump_rules or allowed_types when strict_types: true
• Scope: must be in allowed_scopes (auto-inferred from app names + aliases when not configured) when strict_scopes: true
• No scope: rejected when allow_no_scope: false
• Subject length: max_subject_length, default 100

Return

• :ok — valid
• {:error, reason} — one of:
  • :missing_header
  • :bad_format
  • {:unknown_type, type, allowed}
  • {:unknown_scope, scope, allowed}
  • :scope_required
  • {:subject_too_long, length, max}