分層付款（tier 2）：x402（USDC on Base）付款後回短命簽章收據，供 gauge-frontdesk /pay/verify 驗證。?ref=<query hash>（選）。

[BATCH+PROOF] Stablecoin death register - terminated below 0.10 or persistently absent. Add ?verifiable=1 for per-row _hash_core, fully offline-recomputable. A neutral observation record: not a rating, not an endorsement. Descriptive only, never a forecast or advice. No data -> 422 no_charge, not billed. $0.09 per call.