fix: decisions not skipped when encountered in _emitBranch walk

- _emitBranch walk no longer adds decisions to visited before calling
  generateCode — let the decision's own generateCode manage its visited
  tracking. Otherwise the decision's generateCode sees itself as already
  visited and returns empty, dropping its entire subtree.
- Same fix in both codegen/index.js and blocks-algo.js

blocks-algo.js

@@ -258,13 +258,14 @@ class WCDecision extends WCBlock {
         }
         return;
       }
-      visited.add(el);
-      if (loopTargets && loopTargets.has(el)) {
-        c += "\n" + el.id + ":";
-      }
       if (el instanceof WCDecision) {
+        // Decisions manage their own visited tracking inside generateCode.
         c += el.generateCode(visited, loopTargets);
       } else {
+        visited.add(el);
+        if (loopTargets && loopTargets.has(el)) {
+          c += "\n" + el.id + ":";
+        }
         c += el.generateOwnCode();
         for (const p of el.wcNextFlow) walk(p.toElement);
       }

codegen/index.js

@@ -107,15 +107,14 @@
         }
         return;
       }
-      visited.add(el);
-
-      if (loopTargets.has(el)) {
-        parts.push("\n" + (el.id || "block") + ":");
-      }
-
       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") + ":");
+        }
         parts.push(el.generateOwnCode());
         var flow = el.wcNextFlow || el.nextFlow || [];
         for (var j = 0; j < flow.length; j++) {