diff --git a/src/adapters/browser-transfer/resumable-upload/http-control-plane-adapter.ts b/src/adapters/browser-transfer/resumable-upload/http-control-plane-adapter.ts
index ced99e3..99cb96e 100644
--- a/src/adapters/browser-transfer/resumable-upload/http-control-plane-adapter.ts
+++ b/src/adapters/browser-transfer/resumable-upload/http-control-plane-adapter.ts
@@ -104,7 +104,7 @@ export function createResumableUploadHttpControlPlane(
           "UPLOAD_SESSION",
         );
         if (!response.ok) return response;
-        const session = decodeSession(response.value);
+        const session = decodeSafely(decodeSession, response.value);
         return session
           ? browserDataSuccess(session)
           : browserDataFailure(
@@ -140,7 +140,7 @@ export function createResumableUploadHttpControlPlane(
           "UPLOAD_RECONCILE",
         );
         if (!response.ok) return response;
-        const status = decodeStatus(response.value);
+        const status = decodeSafely(decodeStatus, response.value);
         return status
           ? browserDataSuccess(status)
           : browserDataFailure(
@@ -270,7 +270,7 @@ export function createResumableUploadHttpControlPlane(
           "UPLOAD_COMPLETE",
         );
         if (!response.ok) return response;
-        const completed = decodeCompletion(response.value);
+        const completed = decodeSafely(decodeCompletion, response.value);
         return completed
           ? browserDataSuccess(completed)
           : browserDataFailure(
@@ -579,6 +579,15 @@ function snapshotReceipt(value: UploadPartReceipt): UploadPartReceipt {
   return Object.freeze({ ...value });
 }
 
+/**
+ * TR-RR-08. `Object.keys` sees only enumerable own string keys, so a symbol or
+ * non-enumerable extra field passed unseen and a later property read invoked
+ * whatever accessor the sender installed — escaping the Result contract as a
+ * rejection of the public method.
+ *
+ * Every key is checked against its own property descriptor, and the whole probe
+ * runs inside a catch so a proxy trap is a decode failure, not an exception.
+ */
 function exactKeys(
   value: unknown,
   keys: readonly string[],
@@ -586,12 +595,39 @@ function exactKeys(
   if (!value || typeof value !== "object" || Array.isArray(value)) {
     return false;
   }
-  const actual = Object.keys(value).sort();
-  const expected = [...keys].sort();
-  return (
-    actual.length === expected.length &&
-    actual.every((key, index) => key === expected[index])
-  );
+  try {
+    if (Object.getOwnPropertySymbols(value).length > 0) return false;
+    const actual = Object.getOwnPropertyNames(value).sort();
+    const expected = [...keys].sort();
+    if (
+      actual.length !== expected.length ||
+      actual.some((key, index) => key !== expected[index])
+    ) {
+      return false;
+    }
+    return actual.every((key) => {
+      const descriptor = Object.getOwnPropertyDescriptor(value, key);
+      return Boolean(descriptor && "value" in descriptor);
+    });
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * TR-RR-08. Runs a decoder inside the adapter's failure boundary. A hostile
+ * object that still throws from a trap becomes a typed `CORRUPT_DATA` result
+ * rather than a native rejection out of a public method.
+ */
+function decodeSafely<Value>(
+  decode: (value: unknown) => Value | null,
+  value: unknown,
+): Value | null {
+  try {
+    return decode(value);
+  } catch {
+    return null;
+  }
 }
 
 function safeIdempotencyKey(value: string): boolean {
diff --git a/tests/unit/resumable-upload-http-control-plane.test.ts b/tests/unit/resumable-upload-http-control-plane.test.ts
index e34709f..7647f5b 100644
--- a/tests/unit/resumable-upload-http-control-plane.test.ts
+++ b/tests/unit/resumable-upload-http-control-plane.test.ts
@@ -158,6 +158,111 @@ function rangeSource(bytes: Uint8Array) {
 }
 
 describe("resumable upload HTTP control plane", () => {
+  /**
+   * TR-RR-08. `Object.keys` sees only enumerable own string keys, so a symbol
+   * or non-enumerable extra passed unseen and a later property read invoked
+   * whatever accessor the sender installed — escaping the Result contract as a
+   * rejection of a public method.
+   */
+  it("closes every hostile control-plane object as typed CORRUPT_DATA", async () => {
+    const fingerprint: UploadFileFingerprint = Object.freeze({
+      algorithm: "SHA-256-PARTS-V1",
+      digestHex: "a".repeat(64),
+      byteLength: 4,
+      partSizeBytes: 4,
+      partCount: 1,
+    });
+    const validSession = () => ({
+      protocol: RESUMABLE_UPLOAD_PROTOCOL,
+      sessionId: "session_01",
+      requestBindingSha256: "b".repeat(64),
+      fingerprint,
+      partSizeBytes: 4,
+      partCount: 1,
+      maxConcurrency: 1,
+      expiresAtEpochMs: NOW + 10_000,
+    });
+
+    const hostile: readonly (readonly [string, () => unknown])[] = [
+      [
+        "throwing getter",
+        () => {
+          const value = validSession() as Record<string, unknown>;
+          Object.defineProperty(value, "sessionId", {
+            configurable: true,
+            enumerable: true,
+            get: () => {
+              throw new TypeError("hostile getter");
+            },
+          });
+          return value;
+        },
+      ],
+      [
+        "symbol key",
+        () => ({ ...validSession(), [Symbol("injected")]: "leak" }),
+      ],
+      [
+        "non-enumerable extra",
+        () => {
+          const value = validSession() as Record<string, unknown>;
+          Object.defineProperty(value, "signedUrl", {
+            configurable: true,
+            enumerable: false,
+            value: "https://objects.example/secret?signature=leak",
+          });
+          return value;
+        },
+      ],
+      [
+        "ownKeys trap",
+        () =>
+          new Proxy(validSession() as Record<string, unknown>, {
+            ownKeys() {
+              throw new TypeError("hostile ownKeys");
+            },
+          }),
+      ],
+      [
+        "getOwnPropertyDescriptor trap",
+        () =>
+          new Proxy(validSession() as Record<string, unknown>, {
+            getOwnPropertyDescriptor() {
+              throw new TypeError("hostile descriptor");
+            },
+          }),
+      ],
+    ];
+
+    for (const [label, build] of hostile) {
+      const control = createResumableUploadHttpControlPlane({
+        transport: {
+          async execute() {
+            return browserDataSuccess(build());
+          },
+        },
+        partCapabilities: { issueUploadPart: vi.fn() },
+      });
+      const result = await control.createSession({
+        protocol: RESUMABLE_UPLOAD_PROTOCOL,
+        uploadKey: "upload_key_strict",
+        purpose: "attachment",
+        mediaType: "application/octet-stream",
+        requestBindingSha256: "b".repeat(64),
+        fingerprint,
+        requestedPartSizeBytes: 4,
+        requestedMaxConcurrency: 1,
+        idempotencyKey: "upload-create-idempotency-01",
+        signal: activeSignal,
+      });
+      expect(result, label).toMatchObject({
+        ok: false,
+        error: { code: "CORRUPT_DATA", operation: "UPLOAD_SESSION" },
+      });
+      expect(JSON.stringify(result)).not.toContain("signature=leak");
+    }
+  });
+
   it("rejects unknown response fields so URLs cannot cross the DTO boundary", async () => {
     const fingerprint: UploadFileFingerprint = Object.freeze({
       algorithm: "SHA-256-PARTS-V1",