programs-react: propagate arg names from callee JUMPDEST

The invoke spec change moved argument pointers from the
caller JUMP to the callee entry JUMPDEST. The call stack
builder was updating argumentPointers from the duplicate
callee step but not argumentNames, causing names to show
as _0 instead of the actual parameter name.

Author: gnidan

packages/programs-react/src/utils/mockTrace.ts

@@ -315,9 +315,11 @@ export function buildCallStack(
       if (isDuplicate) {
         // Use the callee entry step for resolution —
         // the argument pointers reference stack slots
-        // that are valid at the JUMPDEST, not the JUMP
+        // that are valid at the JUMPDEST, not the JUMP.
+        // Argument names also live on the callee entry.
         const argResult = extractArgInfo(instruction);
         top.stepIndex = i;
+        top.argumentNames = argResult?.names ?? top.argumentNames;
         top.argumentPointers = argResult?.pointers;
       } else {
         const argResult = extractArgInfo(instruction);