diff --git a/src/domain/conformanceTrustGate.ts b/src/domain/conformanceTrustGate.ts
index 1642a721c..0b3e02b1c 100644
--- a/src/domain/conformanceTrustGate.ts
+++ b/src/domain/conformanceTrustGate.ts
@@ -319,11 +319,11 @@ function sortKeys(value: unknown): unknown {
   if (value === null || typeof value !== "object") return value;
   if (Array.isArray(value)) return value.map(sortKeys);
   if (!isRecord(value)) return value;
-  const sorted: Record<string, unknown> = {};
-  for (const key of Object.keys(value).sort()) {
-    sorted[key] = sortKeys(value[key]);
-  }
-  return sorted;
+  return Object.fromEntries(
+    Object.keys(value)
+      .sort()
+      .map((key) => [key, sortKeys(value[key])]),
+  );
 }
 
 /**
diff --git a/tests/conformance/providers/conformanceReplay.test.ts b/tests/conformance/providers/conformanceReplay.test.ts
index 6cce9cc28..eda3b2f20 100644
--- a/tests/conformance/providers/conformanceReplay.test.ts
+++ b/tests/conformance/providers/conformanceReplay.test.ts
@@ -262,3 +262,53 @@ describe("conformance replay package boundary", () => {
     ).rejects.toThrow(/replay_plans references unknown scenario missing/u);
   });
 });
+
+describe("conformance structured JSON drift", () => {
+  it("detects an added own __proto__ field in captured JSON as drift", async () => {
+    const expected = createEvidence(
+      undefined,
+      { id: "fixture-provider", name: "Fixture provider", version: "1" },
+      { operation: "run", parameters: {}, result: { filesystem: {} } },
+    );
+    const pkg = createConformancePackage({
+      ...validPackageInput,
+      expected_evidence: [
+        {
+          scenario_id: "s1",
+          envelopes: [expected],
+          bundle: null,
+          required_dimensions: ["filesystem"],
+        },
+      ],
+      verifier_contracts: [
+        {
+          scenario_id: "s1",
+          dimensions: [
+            { name: "filesystem", required: true, comparison: "semantic" },
+          ],
+          timing_tolerance_ms: 0,
+        },
+      ],
+    });
+    const captured: unknown = JSON.parse('{"__proto__":{"added":true}}');
+    const actualEvidenceId = `ev_${"4".repeat(64)}`;
+    const result = await replayConformancePackage(
+      pkg,
+      {
+        s1: {
+          evidence_id: actualEvidenceId,
+          normalized_result: { filesystem: captured },
+        },
+      },
+      passingRunner,
+    );
+
+    expect(result.drift_detected).toBe(true);
+    expect(result.trust_gate_results[0]?.verdict).toBe("fail");
+    expect(result.first_drift).toMatchObject({
+      scenario_id: "s1",
+      dimension: "filesystem",
+      evidence_id: actualEvidenceId,
+    });
+  });
+});
diff --git a/tests/conformance/providers/conformanceTrustGate.test.ts b/tests/conformance/providers/conformanceTrustGate.test.ts
index 5052066c8..4de72fb96 100644
--- a/tests/conformance/providers/conformanceTrustGate.test.ts
+++ b/tests/conformance/providers/conformanceTrustGate.test.ts
@@ -198,3 +198,39 @@ describe("conformance trust gates", () => {
     expect(result.verdict).toBe("fail");
   });
 });
+
+describe("conformance structured JSON comparison", () => {
+  it.each([
+    ['{"__proto__":{"version":1}}', '{"__proto__":{"version":2}}'],
+    ['{"__proto__":"before"}', '{"__proto__":"after"}'],
+    ["{}", '{"__proto__":null}'],
+    [
+      '{"entries":[{"payload":{"__proto__":{"version":1}}}]}',
+      '{"entries":[{"payload":{"__proto__":{"version":2}}}]}',
+    ],
+    ['{"constructor":1}', '{"constructor":2}'],
+    ['{"prototype":1}', '{"prototype":2}'],
+  ])("preserves changed own JSON keys in %s", (before, after) => {
+    const expected: unknown = JSON.parse(before);
+    const actual: unknown = JSON.parse(after);
+
+    expect(compareDimension("filesystem", expected, actual)).toMatchObject({
+      status: "mismatch",
+    });
+    expect(JSON.stringify(expected)).toBe(before);
+    expect(JSON.stringify(actual)).toBe(after);
+  });
+
+  it("ignores key order while preserving own JSON keys in nested objects", () => {
+    const expected: unknown = JSON.parse(
+      '{"__proto__":{"a":1,"b":2},"constructor":[{"x":1,"prototype":2}]}',
+    );
+    const actual: unknown = JSON.parse(
+      '{"constructor":[{"prototype":2,"x":1}],"__proto__":{"b":2,"a":1}}',
+    );
+
+    expect(compareDimension("filesystem", expected, actual)).toMatchObject({
+      status: "match",
+    });
+  });
+});