Anonymous: flatten preview
No auth required. Flattens a domain's SPF record and returns recognized senders, warnings, and the post-flatten lookup count. A domain publishing more than one SPF record is a permerror with nothing to flatten: that returns 400 with error set to multiple_spf_records and the colliding records in spf_records.
GET /api/py/flatten-preview?domain=example.com
{
"domain": "example.com",
"flattened_spf": "v=spf1 ip4:... -all",
"lookup_count": 3,
"recognized": [...],
"warnings": []
}