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Asim Aslam 7e3d2d3b13 x402: harden spend cap — reject invalid amounts, require settler option (#4831)
Two spend-safety fixes from the gap audit (#4814):

- Client.Do refused a 402 only on the budget check, but parsed
  maxAmountRequired with a swallowed error, so a non-decimal, overflowing
  or negative amount became 0 and passed the cap trivially while Payer.Pay
  still signed against the string. Now reject any amount that is not a
  positive integer before signing.

- Require settled only when the facilitator implemented Settler; a
  verify-only facilitator served the resource while no funds moved. Add
  Config.RequireSettlement to fail closed in that case.

Tests cover invalid/negative/overflow amounts and the verify-only
fail-closed path.


Claude-Session: https://claude.ai/code/session_01CmdEY7pYmV5zzwCjNJ4ykL

Co-authored-by: Claude <noreply@anthropic.com>
2026-07-12 12:40:12 +01:00
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