feat: back next questions with explicit graph unknowns

tests/graph/apply-proposal.test.js

@@ -1133,6 +1133,9 @@ describe("applyValidatedProposal", () => {
     expect(result.resolvedReasoningNodeIds).toEqual([
       "reasoning:comparability",
     ]);
+    expect(result.emergentReasoningNodeCreated).toBe(true);
+    expect(result.emergentReasoningNodeId).toBeTruthy();
+    expect(result.emergentReasoningNodeReason).toContain("backed by the graph");
     expect(result.previousReasoningState.comparabilityStatus).toBe("uncertain");
     expect(result.reasoningState).toMatchObject({
       comparabilityStatus: "confirmed",
@@ -1142,6 +1145,7 @@ describe("applyValidatedProposal", () => {
     expect(result.reasoningState.comparabilityEvidence).toEqual([
       comparabilityUnknownId,
     ]);
+    expect(result.selectedQuestion?.nodeId).toBe(result.newActiveUnknownNodeId);
     expect(result.selectedQuestion?.question).toMatch(
       /^What changed during that period that could help explain why /,
     );
@@ -1163,6 +1167,27 @@ describe("applyValidatedProposal", () => {
           "The observations concern connected business signals but do not establish a direct contradiction or cause.",
       },
     ]);
+    const emergentNode = result.updatedSituationGraph.nodes.find(
+      (node) => node.id === result.emergentReasoningNodeId,
+    );
+    expect(emergentNode).toMatchObject({
+      kind: "unknown",
+      status: "unknown",
+      confidence: "medium",
+    });
+    expect(emergentNode.description.toLowerCase()).toContain("because");
+    expect(
+      result.updatedSituationGraph.edges.filter(
+        (edge) => edge.toNodeId === result.emergentReasoningNodeId,
+      ),
+    ).not.toEqual([]);
+    expect(
+      result.updatedSituationGraph.edges.some(
+        (edge) =>
+          edge.toNodeId === result.emergentReasoningNodeId &&
+          edge.relationship === "causes",
+      ),
+    ).toBe(false);
     expect(
       JSON.stringify(
         result.updatedSituationGraph.nodes.find(
@@ -1171,4 +1196,40 @@ describe("applyValidatedProposal", () => {
       ),
     ).toBe(originalUnrelatedNode);
   });
+
+  it("reuses an equivalent existing unresolved reasoning unknown instead of creating a duplicate", () => {
+    const { graph, proposal } = makeComparabilityUpdateFixture();
+    graph.nodes.push(
+      makeNode({
+        id: "n-existing-explanation",
+        label:
+          "Explanation for why Revenue increased by 18%, but cash in the bank fell over the same period",
+        description:
+          "Need to understand what change or event could explain why these observations differ, because that is needed to investigate their relationship.",
+        kind: "unknown",
+        status: "unknown",
+        confidence: "medium",
+      }),
+    );
+
+    const result = applyValidatedProposal({
+      situationGraph: graph,
+      proposal,
+      previousQuestion:
+        "Were these figures measured on the same basis and at the same scale?",
+      answer:
+        "Yes. Both figures cover the same accounting period and are taken from the same management accounts.",
+    });
+
+    expect(result.success).toBe(true);
+    expect(result.emergentReasoningNodeCreated).toBe(false);
+    expect(result.emergentReasoningNodeId).toBe("n-existing-explanation");
+    expect(result.newActiveUnknownNodeId).toBe("n-existing-explanation");
+    expect(result.selectedQuestion?.nodeId).toBe("n-existing-explanation");
+    expect(
+      result.updatedSituationGraph.nodes.filter(
+        (node) => node.label === graph.nodes.at(-1).label,
+      ),
+    ).toHaveLength(1);
+  });
 });