feat: explain deterministic unknown selection

tests/graph/orchestrator.test.js

@@ -178,6 +178,9 @@ describe("lib/graph/orchestrator startCase", () => {
 
     expect(result.success).toBe(true);
     expect(result.situationGraph.activeUnknownNodeId).toBeTruthy();
+    expect(result.diagnostics.unknownSelectionExplanation?.selectedNodeId).toBe(
+      result.situationGraph.activeUnknownNodeId,
+    );
   });
 
   it("returns structured failure when graph reference validation fails", async () => {
@@ -262,6 +265,69 @@ describe("lib/graph/orchestrator startCase", () => {
     expect(result.diagnostics.compatibilityChanges).toHaveLength(1);
   });
 
+  it("preserves selected question bytes while adding selection explanation diagnostics", async () => {
+    const { updateCase } = await import("@/lib/graph/orchestrator.js");
+    const provider = {
+      generateReconstruction: vi.fn().mockResolvedValue(
+        makeProposal({
+          addedNodes: [
+            makeNode({
+              id: "n-build-decision",
+              label: "Build Confidence Engine decision",
+              description: "Decision introduced by the answer.",
+              kind: "state",
+              status: "supported",
+              confidence: "medium",
+            }),
+            makeNode({
+              id: "n-commercial-value",
+              label: "Commercial value definition",
+              description:
+                "Need a concrete definition because the decision depends on it.",
+              kind: "unknown",
+              status: "unknown",
+              confidence: "high",
+            }),
+          ],
+          addedEdges: [
+            {
+              id: "e-build-commercial-value",
+              fromNodeId: "n-build-decision",
+              toNodeId: "n-commercial-value",
+              relationship: "depends_on",
+              confidence: "medium",
+              description:
+                "The decision depends on commercial value definition.",
+            },
+          ],
+          selectedQuestion: {
+            nodeId: "n-commercial-value",
+            question:
+              "How should commercial value be defined for this decision?",
+            reason: "Consequential unresolved uncertainty remains.",
+          },
+        }),
+      ),
+    };
+
+    const first = await updateCase(makeUpdateRequest(), {
+      provider,
+      config: MOCK_CONFIG,
+      applyProposal: true,
+    });
+    const second = await updateCase(makeUpdateRequest(), {
+      provider,
+      config: MOCK_CONFIG,
+      applyProposal: true,
+    });
+
+    expect(first.selectedQuestion.question).toBe(
+      second.selectedQuestion.question,
+    );
+    expect(first.selectedQuestion.reason).toBe(second.selectedQuestion.reason);
+    expect(first.diagnostics.unknownSelectionExplanation).toBeTruthy();
+  });
+
   it("produces a validated update proposal for a valid request", async () => {
     const { updateCase } = await import("@/lib/graph/orchestrator.js");
     const provider = {