test(harness): preserve null-question start captures

scripts/reproduce-multi-turn-investigation.mjs

@@ -462,8 +462,10 @@ async function runStartOnlyMode() {
   console.log(`node count: ${nodeCount(situationGraph)}`);
   console.log(`edge count: ${edgeCount(situationGraph)}`);
 
-  if (!selectedQuestion) {
-    console.log("ERROR: No selected question returned from start. Cannot persist continuation state.");
+  // Null selectedQuestion is a valid Start outcome (active target, no graph-backed question available).
+  // Only genuine failure (no success flag or missing graph) should block.
+  if (!situationGraph || !Array.isArray(situationGraph.nodes)) {
+    console.log("ERROR: Invalid Start response — missing situationGraph.");
     process.exitCode = 1;
     return;
   }