diff --git a/lib/graph/orchestrator.js b/lib/graph/orchestrator.js
index cbbc894..2f561ca 100644
--- a/lib/graph/orchestrator.js
+++ b/lib/graph/orchestrator.js
@@ -17,6 +17,7 @@ import { applyValidatedProposal } from "./apply-proposal.js";
 import { buildGraphUpdatePrompt } from "./prompt-builder.js";
 import { parseGraphUpdateProposal } from "./update-proposal.js";
 import {
+  explainUnknownSelection,
   selectActiveUnknownCandidate,
   validateGraphReferences,
 } from "./utils.js";
@@ -31,7 +32,12 @@ function toValidationErrors(error) {
   );
 }
 
-function buildDiagnostics({ analysis, graph, graphReferenceValidation }) {
+function buildDiagnostics({
+  analysis,
+  graph,
+  graphReferenceValidation,
+  unknownSelectionExplanation,
+}) {
   return {
     promptVersion: analysis?.promptVersion ?? null,
     modelName: analysis?.modelName ?? null,
@@ -43,6 +49,7 @@ function buildDiagnostics({ analysis, graph, graphReferenceValidation }) {
     compatibilityApplied: analysis?.compatibilityApplied ?? false,
     compatibilityChanges: analysis?.compatibilityChanges ?? [],
     compatibilityWarnings: analysis?.compatibilityWarnings ?? [],
+    unknownSelectionExplanation: unknownSelectionExplanation ?? null,
   };
 }
 
@@ -54,6 +61,7 @@ function buildUpdateDiagnostics({
   graph,
   graphReferenceValidation,
   selectedQuestion,
+  unknownSelectionExplanation,
 }) {
   return {
     promptVersion: promptVersion ?? "v0.4",
@@ -71,6 +79,7 @@ function buildUpdateDiagnostics({
       selectedQuestion?.investigationStrategy ??
       selectedQuestion?.strategy ??
       null,
+    unknownSelectionExplanation: unknownSelectionExplanation ?? null,
   };
 }
 
@@ -131,6 +140,10 @@ export async function startCase(body) {
   situationGraphSchema.parse(situationGraph);
 
   const graphReferenceValidation = validateGraphReferences(situationGraph);
+  const unknownSelectionExplanation = explainUnknownSelection(
+    situationGraph,
+    [],
+  );
   if (!graphReferenceValidation.valid) {
     return {
       success: false,
@@ -139,6 +152,7 @@ export async function startCase(body) {
         analysis,
         graph: situationGraph,
         graphReferenceValidation,
+        unknownSelectionExplanation,
       }),
       validationErrors: graphReferenceValidation.errors,
       statusCode: 500,
@@ -153,6 +167,7 @@ export async function startCase(body) {
       analysis,
       graph: situationGraph,
       graphReferenceValidation,
+      unknownSelectionExplanation,
     }),
   };
 }
@@ -290,6 +305,10 @@ async function updateCaseWithDependencies(body, dependencies = {}) {
             graph: situationGraph,
             graphReferenceValidation: graphReferenceValidation,
             selectedQuestion: null,
+            unknownSelectionExplanation: explainUnknownSelection(
+              situationGraph,
+              situationGraph.resolvedNodeIds || [],
+            ),
           }),
         },
         statusCode:
@@ -320,6 +339,10 @@ async function updateCaseWithDependencies(body, dependencies = {}) {
         graph: applicationResult.updatedSituationGraph,
         graphReferenceValidation: applicationResult.graphReferenceValidation,
         selectedQuestion: applicationResult.selectedQuestion,
+        unknownSelectionExplanation: explainUnknownSelection(
+          applicationResult.updatedSituationGraph,
+          applicationResult.updatedSituationGraph.resolvedNodeIds || [],
+        ),
       }),
     };
   }
@@ -336,6 +359,10 @@ async function updateCaseWithDependencies(body, dependencies = {}) {
       graph: situationGraph,
       graphReferenceValidation,
       selectedQuestion: null,
+      unknownSelectionExplanation: explainUnknownSelection(
+        situationGraph,
+        situationGraph.resolvedNodeIds || [],
+      ),
     }),
   };
 }
diff --git a/lib/graph/utils.js b/lib/graph/utils.js
index c1fc6cc..cd2cebf 100644
--- a/lib/graph/utils.js
+++ b/lib/graph/utils.js
@@ -95,6 +95,127 @@ function classifyUnknownPriority(text) {
   return matches;
 }
 
+function buildScoreContributions(
+  matches,
+  downstreamCount,
+  unresolvedParentUnknownCount,
+) {
+  const contributions = [
+    {
+      rule: "downstream_dependencies",
+      value: downstreamCount,
+      weight: 4,
+      delta: downstreamCount * 4,
+    },
+  ];
+
+  if (matches.objective) {
+    contributions.push({
+      rule: "objective_match",
+      value: true,
+      weight: 12,
+      delta: 12,
+    });
+  }
+  if (matches.actor) {
+    contributions.push({
+      rule: "actor_match",
+      value: true,
+      weight: 10,
+      delta: 10,
+    });
+  }
+  if (matches.criteria) {
+    contributions.push({
+      rule: "criteria_match",
+      value: true,
+      weight: 11,
+      delta: 11,
+    });
+  }
+  if (matches.measure) {
+    contributions.push({
+      rule: "measure_match",
+      value: true,
+      weight: 8,
+      delta: 8,
+    });
+  }
+  if (matches.terminology) {
+    contributions.push({
+      rule: "terminology_match",
+      value: true,
+      weight: 7,
+      delta: 7,
+    });
+  }
+  if (matches.constraint) {
+    contributions.push({
+      rule: "constraint_match",
+      value: true,
+      weight: 9,
+      delta: 9,
+    });
+  }
+  if (matches.pricing) {
+    contributions.push({
+      rule: "pricing_penalty",
+      value: true,
+      weight: -8,
+      delta: -8,
+    });
+  }
+  if (matches.implementation) {
+    contributions.push({
+      rule: "implementation_penalty",
+      value: true,
+      weight: -10,
+      delta: -10,
+    });
+  }
+  if (matches.optimisation) {
+    contributions.push({
+      rule: "optimisation_penalty",
+      value: true,
+      weight: -9,
+      delta: -9,
+    });
+  }
+  if (matches.speculative) {
+    contributions.push({
+      rule: "speculative_penalty",
+      value: true,
+      weight: -12,
+      delta: -12,
+    });
+  }
+
+  if (
+    matches.pricing &&
+    !matches.objective &&
+    !matches.criteria &&
+    !matches.actor
+  ) {
+    contributions.push({
+      rule: "isolated_pricing_penalty",
+      value: true,
+      weight: -6,
+      delta: -6,
+    });
+  }
+
+  if (unresolvedParentUnknownCount > 0) {
+    contributions.push({
+      rule: "unresolved_prerequisite_penalty",
+      value: unresolvedParentUnknownCount,
+      weight: -7,
+      delta: unresolvedParentUnknownCount * -7,
+    });
+  }
+
+  return contributions;
+}
+
 export function scoreUnknownCandidate(graph, node, resolvedNodeIds = []) {
   const text = collectNodeText(node);
   const matches = classifyUnknownPriority(text);
@@ -105,30 +226,15 @@ export function scoreUnknownCandidate(graph, node, resolvedNodeIds = []) {
     resolvedNodeIds,
   );
 
-  let score = downstreamCount * 4;
-
-  if (matches.objective) score += 12;
-  if (matches.actor) score += 10;
-  if (matches.criteria) score += 11;
-  if (matches.measure) score += 8;
-  if (matches.terminology) score += 7;
-  if (matches.constraint) score += 9;
-
-  if (matches.pricing) score -= 8;
-  if (matches.implementation) score -= 10;
-  if (matches.optimisation) score -= 9;
-  if (matches.speculative) score -= 12;
-
-  if (
-    matches.pricing &&
-    !matches.objective &&
-    !matches.criteria &&
-    !matches.actor
-  ) {
-    score -= 6;
-  }
-
-  score -= unresolvedParentUnknownCount * 7;
+  const contributions = buildScoreContributions(
+    matches,
+    downstreamCount,
+    unresolvedParentUnknownCount,
+  );
+  const score = contributions.reduce(
+    (total, contribution) => total + contribution.delta,
+    0,
+  );
 
   return {
     nodeId: node.id,
@@ -137,6 +243,7 @@ export function scoreUnknownCandidate(graph, node, resolvedNodeIds = []) {
     downstreamCount,
     unresolvedParentUnknownCount,
     matches,
+    contributions,
   };
 }
 
@@ -406,6 +513,102 @@ export function selectActiveUnknownCandidate(graph, resolvedNodeIds) {
   };
 }
 
+export function explainUnknownSelection(graph, resolvedNodeIds = []) {
+  const unresolved = graph.nodes.filter(
+    (n) => n.kind === "unknown" && !resolvedNodeIds.includes(n.id),
+  );
+
+  if (unresolved.length === 0) {
+    return {
+      selectedNodeId: null,
+      selectedNodeLabel: null,
+      resolvedNodeIds: [...resolvedNodeIds],
+      candidates: [],
+      competitors: [],
+      tieBreakOrder: [
+        "score_desc",
+        "downstreamCount_desc",
+        "unresolvedParentUnknownCount_asc",
+        "label_asc",
+      ],
+      summary: {
+        candidateCount: 0,
+      },
+    };
+  }
+
+  const candidates = unresolved.map((node) => ({
+    nodeId: node.id,
+    label: node.label,
+    ...scoreUnknownCandidate(graph, node, resolvedNodeIds),
+  }));
+
+  candidates.sort((a, b) => {
+    if (b.score !== a.score) return b.score - a.score;
+    if (b.downstreamCount !== a.downstreamCount) {
+      return b.downstreamCount - a.downstreamCount;
+    }
+    if (a.unresolvedParentUnknownCount !== b.unresolvedParentUnknownCount) {
+      return a.unresolvedParentUnknownCount - b.unresolvedParentUnknownCount;
+    }
+    return a.label.localeCompare(b.label);
+  });
+
+  const selected = candidates[0];
+  const competitors = candidates.slice(1).map((candidate) => ({
+    nodeId: candidate.nodeId,
+    label: candidate.label,
+    score: candidate.score,
+    downstreamCount: candidate.downstreamCount,
+    unresolvedParentUnknownCount: candidate.unresolvedParentUnknownCount,
+    matches: candidate.matches,
+    contributions: candidate.contributions,
+    outrankedBy: {
+      scoreDelta: selected.score - candidate.score,
+      downstreamDelta: selected.downstreamCount - candidate.downstreamCount,
+      unresolvedPrerequisiteDelta:
+        candidate.unresolvedParentUnknownCount -
+        selected.unresolvedParentUnknownCount,
+      labelOrderWinner:
+        selected.score === candidate.score &&
+        selected.downstreamCount === candidate.downstreamCount &&
+        selected.unresolvedParentUnknownCount ===
+          candidate.unresolvedParentUnknownCount
+          ? selected.label.localeCompare(candidate.label) <= 0
+            ? selected.label
+            : candidate.label
+          : null,
+    },
+  }));
+
+  return {
+    selectedNodeId: selected.nodeId,
+    selectedNodeLabel: selected.label,
+    resolvedNodeIds: [...resolvedNodeIds],
+    tieBreakOrder: [
+      "score_desc",
+      "downstreamCount_desc",
+      "unresolvedParentUnknownCount_asc",
+      "label_asc",
+    ],
+    candidates,
+    selected: {
+      nodeId: selected.nodeId,
+      label: selected.label,
+      score: selected.score,
+      downstreamCount: selected.downstreamCount,
+      unresolvedParentUnknownCount: selected.unresolvedParentUnknownCount,
+      matches: selected.matches,
+      contributions: selected.contributions,
+    },
+    competitors,
+    summary: {
+      candidateCount: candidates.length,
+      selectedReason: `highest_score=${selected.score}; downstream=${selected.downstreamCount}; unresolved_prerequisites=${selected.unresolvedParentUnknownCount}`,
+    },
+  };
+}
+
 // ── Apply a graph update deterministically ──
 
 export function applyGraphUpdate(graph, update) {
diff --git a/tests/graph/orchestrator.test.js b/tests/graph/orchestrator.test.js
index 3a61642..2c241fa 100644
--- a/tests/graph/orchestrator.test.js
+++ b/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 = {