v0.12.213 — fix stale pre-auth underpay 500 under per-request pricing (#188)

v0.12.213 — June 26, 2026

Fix an HTTP 500 (Failed to parse payment requirements) that broke paid Base-chain calls whenever a small request seeded the pre-auth cache before a larger one (#188, thanks @KillerQueen-Z).

Pre-auth no longer reuses a stale amount under per-request pricing

• Root cause: the pre-auth cache (payment-preauth.ts) is keyed path:model and stores a single signed amount, but BlockRun prices each call on input tokens + max_tokens — so the same model costs different amounts across requests. When a later request needed more than the cached amount, the signed payment underpaid; the gateway rejected it with a 402 that is not a fresh x402 challenge, and the old code reused that rejection as the challenge → getPaymentRequiredResponse threw → HTTP 500.
• Impact: every paid Base model failed once a cheaper request seeded the cache before a larger one (any growing/agentic usage — Codex, long contexts). Reproduced on a clean npx @blockrun/clawrouter@latest: 12/12 paid models failed tiny→large; a 10-turn coding conversation failed ~50% of turns. Not affected: free models (no payment) and Solana (skipPreAuth).
• Fix (three guards): (1) never knowingly underpay — reuse a cached pre-auth only when the up-front estimateAmount (already used for balance checks) proves the cached amount still covers this request; (2) safety net — if a pre-auth is rejected anyway, discard it and re-request without payment to get a fresh, canonical challenge, never treating the rejection as the challenge; (3) fail safe — when no estimate is available, skip pre-auth rather than risk an underpay. The fast path (cached amount covers the request) still pre-signs and skips the 402 round-trip; only would-be underpays fall back to the normal flow.
• Tests: new src/payment-preauth.test.ts (reuse-when-covered / skip-on-growth / reject-then-refetch / no-estimator); full suite 623 passed, lint + typecheck clean.