fix(evm-wallet-experiment): reserve spend budget before await, rollback on failure

Committing after redeemFn resolved left a window where two concurrent
calls could both pass the remaining() check and together exceed the
budget. Commit before the await to atomically reserve the budget, then
rollback if redeemFn throws. This is the pattern rollback() was designed
for but was never called.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: grypez

packages/evm-wallet-experiment/src/lib/delegation-twin.ts

@@ -177,18 +177,24 @@ export function makeDelegationTwin(
           `Insufficient budget: requested ${trackAmount}, remaining ${tracker.remaining()}`,
         );
       }
+      // Reserve before the await so concurrent calls see the updated budget
+      // and cannot both pass the check. Roll back if redeemFn fails.
+      tracker.commit(trackAmount);
     }
 
     const execution = entry.buildExecution(
       token ?? ('' as Address),
       normalizedArgs,
     );
 
-    const txHash = await redeemFn(execution);
-    if (tracker && trackAmount !== undefined) {
-      tracker.commit(trackAmount);
+    try {
+      return await redeemFn(execution);
+    } catch (error) {
+      if (tracker && trackAmount !== undefined) {
+        tracker.rollback(trackAmount);
+      }
+      throw error;
     }
-    return txHash;
   };
 
   const methods: Record<string, (...args: unknown[]) => unknown> = {