Cryptographically private AI inference (Arcium-encrypted, x402-paywalled)

OpenAI-compatible chat completions. The prompt MUST be Arcium-encrypted client-side using `@solrouter/sdk`'s `encryptPrompt()` helper; the encrypted prompt is processed and the response returned encrypted, without Solrouter ever seeing plaintext. Pay-per-call x402 ($0.005 USDC flat per call). For per-token internal-credit billing with an API key, use POST /api/v1/chat/completions instead.

curl -X POST "https://example.com/api/v1/x402/chat/completions" \  -H "Content-Type: application/json" \  -d '{    "encryptedPrompt": "base64-arcium-ciphertext...",    "model": "gpt-oss:20b",    "maxTokens": 2048  }'

{
  "encryptedResponse": "base64-arcium-ciphertext...",
  "usage": {
    "prompt_tokens": 18,
    "completion_tokens": 124,
    "total_tokens": 142
  },
  "cost": 0.005
}

{
  "error": "missing_required_fields"
}