fix(reasoning): preserve investigation ownership across selection and question rejection

lib/graph/apply-proposal.js

@@ -2871,6 +2871,9 @@ function reseatSelectionAfterQuestionRejection({
     : { status: "none", nodeId: null };
 }
 
+const QUESTION_FORMULATION_REJECTION_NO_QUESTION_REASON =
+  "The selected investigation target remains active, but its current graph-backed question formulation was rejected as too complex.";
+
 export function determineGraphBackedQuestion({ situationGraph }) {
   const graphSnapshot = cloneJsonSafe(situationGraph);
   let updatedSituationGraph = cloneJsonSafe(situationGraph);
@@ -2937,15 +2940,12 @@ export function determineGraphBackedQuestion({ situationGraph }) {
     initialQuestionRejected &&
     deterministicSelection?.status === "selected"
   ) {
-    deterministicSelection = reseatSelectionAfterQuestionRejection({
-      graph: updatedSituationGraph,
-      deterministicSelection,
-      excludedNodeIds: [deterministicSelection.nodeId],
-    });
-    questionResult = buildSelectedQuestionResult({
-      updatedSituationGraph,
-      deterministicSelection,
-    });
+    questionResult = {
+      ...questionResult,
+      selectedQuestion: null,
+      questionSuppressedReason:
+        QUESTION_FORMULATION_REJECTION_NO_QUESTION_REASON,
+    };
   }
 
   if (
@@ -2971,14 +2971,15 @@ export function determineGraphBackedQuestion({ situationGraph }) {
       ? questionResult.selectedQuestion?.questionSuppressedReason ||
         questionResult.selectedQuestion?.reason ||
         "Eligible unresolved candidates remain tied after initial graph-backed selection."
-      : (updatedSituationGraph.nodes || []).some(
+      : questionResult.questionSuppressedReason ||
+          ((updatedSituationGraph.nodes || []).some(
             (node) =>
               node.kind === "unknown" &&
               !["resolved", "contradicted"].includes(node.status) &&
               !(updatedSituationGraph.resolvedNodeIds || []).includes(node.id),
           )
-        ? "Compatible unresolved candidates remain, but none produced a valid graph-backed question."
-        : "No unresolved unknown candidates remain after initial graph construction.";
+            ? "Compatible unresolved candidates remain, but none produced a valid graph-backed question."
+            : "No unresolved unknown candidates remain after initial graph construction.");
 
   return {
     success: true,

lib/graph/utils.js

@@ -249,7 +249,7 @@ function semanticSignature(candidate) {
   );
 }
 
-function classifyCandidateOrdering(candidates) {
+function classifyCandidateOrdering(candidates, activeNodeId = null) {
   const displayOrder = buildCandidateDisplayOrder(candidates);
   const best = displayOrder[0] ?? null;
   if (!best) {
@@ -319,15 +319,21 @@ function classifyCandidateOrdering(candidates) {
   }
 
   if (topStructuralCandidates.length > 0) {
+    const activeTiedCandidate = activeNodeId
+      ? topStructuralCandidates.find((candidate) => candidate.nodeId === activeNodeId)
+      : null;
+
     return {
       displayOrder,
-      best,
+      best: activeTiedCandidate || best,
       leadingCandidates: topStructuralCandidates,
       status: "selected",
       tieType: "complete_unresolved_tie",
-      usedAlphabeticalOrdering: true,
+      usedAlphabeticalOrdering: activeTiedCandidate ? false : true,
       reason:
-        "Leading candidates remained tied after score, structural, and semantic checks, so the stable deterministic display order was used as the final fallback.",
+        activeTiedCandidate
+          ? "Leading candidates remained tied after score, structural, and semantic checks, so existing active investigation ownership was preserved."
+          : "Leading candidates remained tied after score, structural, and semantic checks, so the stable deterministic display order was used as the final fallback.",
     };
   }
 
@@ -624,6 +630,7 @@ export function selectActiveUnknownCandidate(graph, resolvedNodeIds) {
       ...candidate,
       node,
     })),
+    graph?.activeUnknownNodeId ?? null,
   );
 
   if (selection.status === "ambiguous") {
@@ -690,7 +697,10 @@ export function explainUnknownSelection(graph, resolvedNodeIds = []) {
     ...scoreUnknownCandidate(graph, node, resolvedNodeIds),
   }));
 
-  const selection = classifyCandidateOrdering(candidates);
+  const selection = classifyCandidateOrdering(
+    candidates,
+    graph?.activeUnknownNodeId ?? null,
+  );
   const orderedCandidates = selection.displayOrder;
   const selected = selection.best;
   const competitors = orderedCandidates