fix: seed _generateCallWithError's local visited set from main traversal

- _emitBranch now sets _genVisited on blocks before calling generateOwnCode
  so that proc calls inside loop bodies can seed their error-handling
  visited set from the main traversal, preventing loop-decision re-walk
- Add _noWalkNext flag on proc calls when error handling is active, so
  _emitBranch skips redundant nextFlow walking (the success path was
  already covered by the error-handling branch emission)
- Known issue: shared blocks that are direct roots of emitBranch (from
  the shared set) may still be re-walked when they were already emitted
  by a downstream proc call's error-handling success path

codegen/index.js

@@ -108,18 +108,23 @@
         return;
       }
       if (isDecision(el)) {
-        // Decisions manage their own visited tracking inside generateCode.
         parts.push(el.generateCode(visited, loopTargets));
       } else {
         visited.add(el);
         if (loopTargets.has(el)) {
           parts.push("\n" + (el.id || "block") + ":");
         }
+        el._genVisited = visited;
         parts.push(el.generateOwnCode());
-        var flow = el.wcNextFlow || el.nextFlow || [];
-        for (var j = 0; j < flow.length; j++) {
-          walk(flow[j].toElement);
+        // If the block's generateOwnCode already walked the success path
+        // (e.g. error-handling proc call), don't re-walk its nextFlow.
+        if (!el._noWalkNext) {
+          var flow = el.wcNextFlow || el.nextFlow || [];
+          for (var j = 0; j < flow.length; j++) {
+            walk(flow[j].toElement);
+          }
         }
+        el._noWalkNext = false;
       }
     }
 
@@ -137,7 +142,7 @@
    * then success-exclusive and shared code after it (no else).
    */
   CodeGen.generateCallWithError = function (
-    ifHeader, errTargets, okTargets, isDecision, loopTargets
+    ifHeader, errTargets, okTargets, isDecision, loopTargets, mainVisited
   ) {
     loopTargets = loopTargets || new Set();
     var errAll = CodeGen.branchDescendants(errTargets, isDecision);
@@ -147,7 +152,9 @@
       if (okAll.has(b)) shared.add(b);
     });
 
-    var visited = new Set();
+    // Create a local visited seeded from the main set so blocks walked by
+    // the error/success branches don't pollute the main traversal's set.
+    var visited = new Set(mainVisited || []);
     var errCode = CodeGen.emitBranch(errTargets, shared, visited, isDecision, loopTargets);
     var okCode = CodeGen.emitBranch(okTargets, shared, visited, isDecision, loopTargets);
     var sharedCode = CodeGen.emitBranch(