From b15fc72c4a67a7a0ec6d3bbb4febc19ea727b6f1 Mon Sep 17 00:00:00 2001
From: RBKunnela <aiagentsprompt@gmail.com>
Date: Sat, 23 May 2026 01:19:44 +0300
Subject: [PATCH] fix(micropayment-engine): correct EIP-55 checksum + bytes32
 nonce (Story 15.1)
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Two related blockers preventing the signing path from working with
viem 2.49+ strict validation:

1. verifyingContract literal had wrong EIP-55 checksum (4 letter case-swaps).
   Canonical address (verified via viem getAddress()):
   0x50b0f7224fFC5F4F7685DbcE1B8b7e7B8b8A4A23

2. generateNonce() returned un-prefixed 64-char hex but the call site cast
   it as `0x${string}` — a type-system lie. viem rejected at hashTypedData
   with BytesSizeMismatchError ("expected bytes32, got bytes64"). Fixed
   at the source: nonce is now genuinely 0x-prefixed and the return type
   is honest.

Verified locally with an ad-hoc smoke script (not committed) — signTypedData
returns a 65-byte (132-char hex) signature and a 32-byte (66-char hex)
nonce after these two fixes. Test file in Story 15 (tests/micropayment-engine.test.ts)
will exercise this path properly post-merge.

Audit pass (Task 15.1.3) found no other hardcoded addresses in this file
and the remaining `as` casts on hex types are pre-existing patterns out of
scope for this hotfix.

Closes Task #18

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
---
 src/micropayment-engine.ts | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/micropayment-engine.ts b/src/micropayment-engine.ts
index b22af6a..c6969a0 100644
--- a/src/micropayment-engine.ts
+++ b/src/micropayment-engine.ts
@@ -229,7 +229,7 @@ export class MicropaymentEngine {
       name: 'PayBot',
       version: '1',
       chainId: 8453,
-      verifyingContract: '0x50b0f7224fFc5f4f7685DbcE1B8b7E7B8B8A4A23' as Address,
+      verifyingContract: '0x50b0f7224fFC5F4F7685DbcE1B8b7e7B8b8A4A23' as Address,
     };
 
     const nonce = this.generateNonce() as `0x${string}`;
@@ -338,11 +338,12 @@ export class MicropaymentEngine {
     return `${whole}${fraction}`.replace(/^0+/, '') || '0';
   }
 
-  private generateNonce(): string {
+  private generateNonce(): `0x${string}` {
     const buf = new Uint8Array(32);
     webcrypto.getRandomValues(buf);
-    return Array.from(buf)
+    const hex = Array.from(buf)
       .map(b => b.toString(16).padStart(2, '0'))
       .join('');
+    return `0x${hex}`;
   }
 }
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