False-negative x402 detection for Studio X POST endpoints

[pu-re]

Two submissions for Studio X were automatically rejected with Auto-review could not confirm x402 payment support:

• Submission 84: https://www.studio-x.cc
• Submission 85: https://studio-x.cc

The service exposes machine-readable discovery at:

• https://www.studio-x.cc/.well-known/x402
• https://www.studio-x.cc/openapi.json

Its paid endpoints are POST routes that require a valid JSON body before returning the x402 v2 challenge. For example:

curl -i -X POST https://www.studio-x.cc/api/generate/image \
  -H "Content-Type: application/json" \
  -d '{"model":"black-forest-labs/flux-schnell","prompt":"directory verification"}'\n```\n\nThis returns HTTP 402 with x402 payment requirements. Please re-run review with the OpenAPI request body or add POST-body-aware probing so these routes can be detected.

[pu-re]

Studio X now supports GET discovery challenges on all four generation routes and publishes explicit x402 v2 accepts metadata at https://www.studio-x.cc/.well-known/x402. A fresh submission was accepted as pending (submission_id: 88); the initial probe saw HTTP 402 but did not parse the payment-required response header. The well-known document now contains both x402Version: 2 and per-route accepts arrays, so the scheduled retry should verify it. Please re-run submission 88 if the retry queue does not pick it up.