diff --git a/src/routing/trace.ts b/src/routing/trace.ts
index 169400d8d..daea4db9f 100644
--- a/src/routing/trace.ts
+++ b/src/routing/trace.ts
@@ -465,13 +465,20 @@ function parseCapability(raw: unknown, caps: ParseCaps): RouteCapabilityEvidence
   if (image !== undefined) out.image = image;
   const structuredOutput = unknownable(raw.structuredOutput);
   if (structuredOutput !== undefined) out.structuredOutput = structuredOutput;
-  if (Array.isArray(raw.reasoningEfforts)
-    && raw.reasoningEfforts.slice(0, 8).every((value): value is string => typeof value === "string")) {
-    if (raw.reasoningEfforts.some((value: unknown) => typeof value === "string"
+  const rawReasoningEfforts = Array.isArray(raw.reasoningEfforts)
+    ? raw.reasoningEfforts
+    : undefined;
+  const reasoningEfforts = rawReasoningEfforts
+    ? Array.from(
+      { length: Math.min(rawReasoningEfforts.length, 8) },
+      (_, index) => rawReasoningEfforts[index],
+    )
+    : undefined;
+  if (reasoningEfforts
+    && reasoningEfforts.every((value): value is string => typeof value === "string")) {
+    if (reasoningEfforts.some((value: unknown) => typeof value === "string"
       && value.length > MAX_TRACE_STRING)) caps.strings = true;
-    out.reasoningEfforts = raw.reasoningEfforts
-      .slice(0, 8)
-      .map(value => value.slice(0, MAX_TRACE_STRING));
+    out.reasoningEfforts = reasoningEfforts.map(value => value.slice(0, MAX_TRACE_STRING));
   }
   if (raw.serviceTier === "unknown") {
     out.serviceTier = "unknown";
diff --git a/tests/route-decision-trace.test.ts b/tests/route-decision-trace.test.ts
index 5a0c00579..f90d77f30 100644
--- a/tests/route-decision-trace.test.ts
+++ b/tests/route-decision-trace.test.ts
@@ -223,6 +223,66 @@ describe("route decision traces (RI-01)", () => {
     expect(trace.candidates.every(candidate => candidate.exclusions.length === MAX_EXCLUSIONS_PER_CANDIDATE)).toBe(true);
   });
 
+  test("normalization only inspects retained reasoning efforts", () => {
+    const reasoningEfforts = Array.from({ length: 1_000_000 }) as unknown[];
+    reasoningEfforts.fill("medium", 0, 8);
+    reasoningEfforts[0] = "x".repeat(MAX_TRACE_STRING + 1);
+    Object.defineProperty(reasoningEfforts, 8, {
+      get: () => { throw new Error("reasoning effort outside the retained range was inspected"); },
+    });
+    const raw = {
+      version: 1,
+      decisionId: "abcdef012345",
+      createdAt: 1,
+      requestedModel: "a/m1",
+      routeKind: "policy",
+      requirements: [],
+      candidates: [{
+        provider: "a",
+        model: "m1",
+        eligible: true,
+        exclusions: [],
+        capability: { reasoningEfforts },
+      }],
+      selected: { candidateIndex: 0, provider: "a", model: "m1", reason: "policy" },
+    };
+
+    const normalized = normalizeRouteDecisionTrace(raw);
+    expect(normalized).not.toBeNull();
+    if (!normalized) throw new Error("trace normalization unexpectedly failed");
+    expect(normalized.candidates[0]?.capability?.reasoningEfforts)
+      .toEqual(["x".repeat(MAX_TRACE_STRING), ...Array.from({ length: 7 }, () => "medium")]);
+    expect(normalized.truncated?.strings).toBe(true);
+  });
+
+  test("normalization rejects sparse retained reasoning efforts", () => {
+    const reasoningEfforts = Array(8) as unknown[];
+    reasoningEfforts[0] = "low";
+    reasoningEfforts[7] = "high";
+    const raw = {
+      version: 1,
+      decisionId: "abcdef012345",
+      createdAt: 1,
+      requestedModel: "a/m1",
+      routeKind: "policy",
+      requirements: [],
+      candidates: [{
+        provider: "a",
+        model: "m1",
+        eligible: true,
+        exclusions: [],
+        capability: { reasoningEfforts },
+      }],
+      selected: { candidateIndex: 0, provider: "a", model: "m1", reason: "policy" },
+    };
+
+    const normalized = normalizeRouteDecisionTrace(raw);
+    expect(normalized).not.toBeNull();
+    if (!normalized) throw new Error("trace normalization unexpectedly failed");
+    expect(normalized.candidates).toHaveLength(1);
+    expect(normalized.candidates[0]?.capability?.reasoningEfforts).toBeUndefined();
+  });
+
   test("startup hydration reads trace-sized usage rows", () => {
     const trace = oversizedTrace();
     for (let index = 0; index < 20; index++) {