Invalid rules url

What it means

The request was malformed, or a field failed validation.

Example detail messages returned with this error:

• custom_rules_url must be ≤ 512 chars.
• custom_rules_url must be a public HTTPS URL: {guard.reason}

What to do

Correct the rules_url value - detail names what was wrong.

Response shape

All fremforge API errors are RFC 9457 problem+json:

{
  "type": "https://docs.frem.sh/reference/api/errors/invalid-rules-url",
  "title": "Bad Request",
  "status": 400,
  "detail": "..."
}

Branch on type, not on title or detail - those are human-readable and may be reworded.