For venues

Phase 0 ships stub adapters: demo_swap (constant-rate USDC-d/DEMO) and demo_yield (share accounting). They fake liquidity. They do not enforce policy. The mandate gate stack still runs in full. Every accept or refuse is a real receipt.

x402 is budgeted spend with a nonce memo, then the caller fetches. HTTP 402 on unpaid GET /price/:symbol.