diff --git a/packages/streams/src/ChromeRuntimeStream.test.ts b/packages/streams/src/ChromeRuntimeStream.test.ts
index b1e928216..eaa949691 100644
--- a/packages/streams/src/ChromeRuntimeStream.test.ts
+++ b/packages/streams/src/ChromeRuntimeStream.test.ts
@@ -20,8 +20,10 @@ import {
 const makeEnvelope = (
   value: unknown,
   target: ChromeRuntimeStreamTarget,
+  source: ChromeRuntimeStreamTarget,
 ): MessageEnvelope<unknown> => ({
   target,
+  source,
   payload: value,
 });
 
@@ -34,10 +36,11 @@ const makeRuntime = (extensionId: string = EXTENSION_ID) => {
   const dispatchRuntimeMessage = (
     message: unknown,
     target: ChromeRuntimeStreamTarget = ChromeRuntimeStreamTarget.Background,
+    source: ChromeRuntimeStreamTarget = ChromeRuntimeStreamTarget.Offscreen,
     senderId: string = extensionId,
   ): void => {
     listeners.forEach((listener) =>
-      listener(makeEnvelope(message, target), { id: senderId }),
+      listener(makeEnvelope(message, target, source), { id: senderId }),
     );
   };
 
@@ -69,6 +72,7 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     expect(reader).toBeInstanceOf(ChromeRuntimeReader);
@@ -81,6 +85,7 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const message = { foo: 'bar' };
@@ -94,12 +99,18 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const nextP = reader.next();
     const message1 = { foo: 'bar' };
     const message2 = { fizz: 'buzz' };
-    dispatchRuntimeMessage(message1, undefined, 'other-extension-id');
+    dispatchRuntimeMessage(
+      message1,
+      ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
+      'other-extension-id',
+    );
     dispatchRuntimeMessage(message2);
 
     expect(await nextP).toStrictEqual(makePendingResult(message2));
@@ -110,6 +121,7 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const nextP = reader.next();
@@ -133,20 +145,18 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const nextP = reader.next();
 
     vi.spyOn(console, 'warn');
     const message1 = { foo: 'bar' };
-    // @ts-expect-error Intentional destructive testing
-    dispatchRuntimeMessage(message1, 'foo');
-
-    expect(console.warn).toHaveBeenCalledWith(
-      `ChromeRuntimeReader received message for unexpected target: ${stringify({
-        target: 'foo',
-        payload: message1,
-      })}`,
+    dispatchRuntimeMessage(
+      message1,
+      // @ts-expect-error Intentional destructive testing
+      'foo',
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const message2 = { fizz: 'buzz' };
@@ -159,6 +169,7 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
     expect(listeners).toHaveLength(1);
 
@@ -175,6 +186,7 @@ describe('ChromeRuntimeReader', () => {
     const reader = new ChromeRuntimeReader(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
       onEnd,
     );
 
@@ -192,6 +204,7 @@ describe.concurrent('ChromeRuntimeWriter', () => {
     const writer = new ChromeRuntimeWriter(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     expect(writer).toBeInstanceOf(ChromeRuntimeWriter);
@@ -203,6 +216,7 @@ describe.concurrent('ChromeRuntimeWriter', () => {
     const writer = new ChromeRuntimeWriter(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
 
     const message = { foo: 'bar' };
@@ -210,7 +224,11 @@ describe.concurrent('ChromeRuntimeWriter', () => {
 
     expect(await nextP).toStrictEqual(makePendingResult(undefined));
     expect(runtime.sendMessage).toHaveBeenCalledWith(
-      makeEnvelope(message, ChromeRuntimeStreamTarget.Background),
+      makeEnvelope(
+        message,
+        ChromeRuntimeStreamTarget.Background,
+        ChromeRuntimeStreamTarget.Offscreen,
+      ),
     );
   });
 
@@ -220,6 +238,7 @@ describe.concurrent('ChromeRuntimeWriter', () => {
     const writer = new ChromeRuntimeWriter(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
       onEnd,
     );
 
@@ -237,13 +256,25 @@ describe.concurrent('ChromeRuntimeDuplexStream', () => {
     const duplexStreamP = ChromeRuntimeDuplexStream.make(
       asChromeRuntime(runtime),
       ChromeRuntimeStreamTarget.Background,
-      ChromeRuntimeStreamTarget.Background,
+      ChromeRuntimeStreamTarget.Offscreen,
     );
     dispatchRuntimeMessage(makeAck());
 
     return [await duplexStreamP, { runtime, dispatchRuntimeMessage }] as const;
   };
 
+  it('throws an error when localTarget and remoteTarget are the same', async () => {
+    const { runtime } = makeRuntime();
+
+    await expect(
+      ChromeRuntimeDuplexStream.make(
+        asChromeRuntime(runtime),
+        ChromeRuntimeStreamTarget.Background,
+        ChromeRuntimeStreamTarget.Background,
+      ),
+    ).rejects.toThrow('localTarget and remoteTarget must be different');
+  });
+
   it('constructs a ChromeRuntimeDuplexStream', async () => {
     const [duplexStream] = await makeDuplexStream();
 
diff --git a/packages/streams/src/ChromeRuntimeStream.ts b/packages/streams/src/ChromeRuntimeStream.ts
index 903c77e6c..9ad5e8f65 100644
--- a/packages/streams/src/ChromeRuntimeStream.ts
+++ b/packages/streams/src/ChromeRuntimeStream.ts
@@ -26,10 +26,12 @@ import type { Dispatchable } from './utils.js';
 export enum ChromeRuntimeStreamTarget {
   Background = 'background',
   Offscreen = 'offscreen',
+  Devtools = 'devtools',
 }
 
 export type MessageEnvelope<Payload> = {
   target: ChromeRuntimeStreamTarget;
+  source: ChromeRuntimeStreamTarget;
   payload: Payload;
 };
 
@@ -39,6 +41,7 @@ const isMessageEnvelope = (
   typeof message === 'object' &&
   message !== null &&
   'target' in message &&
+  'source' in message &&
   'payload' in message;
 
 /**
@@ -56,11 +59,14 @@ export class ChromeRuntimeReader<Read extends Json> extends BaseReader<Read> {
 
   readonly #target: ChromeRuntimeStreamTarget;
 
+  readonly #source: ChromeRuntimeStreamTarget;
+
   readonly #extensionId: string;
 
   constructor(
     runtime: ChromeRuntime,
     target: ChromeRuntimeStreamTarget,
+    source: ChromeRuntimeStreamTarget,
     onEnd?: OnEnd,
   ) {
     // eslint-disable-next-line prefer-const
@@ -76,6 +82,7 @@ export class ChromeRuntimeReader<Read extends Json> extends BaseReader<Read> {
 
     this.#receiveInput = super.getReceiveInput();
     this.#target = target;
+    this.#source = source;
     this.#extensionId = runtime.id;
 
     messageListener = this.#onMessage.bind(this);
@@ -99,11 +106,11 @@ export class ChromeRuntimeReader<Read extends Json> extends BaseReader<Read> {
       return;
     }
 
-    if (message.target !== this.#target) {
-      console.warn(
-        `ChromeRuntimeReader received message for unexpected target: ${stringify(
-          message,
-        )}`,
+    if (message.target !== this.#target || message.source !== this.#source) {
+      console.debug(
+        `ChromeRuntimeReader received message with incorrect target or source: ${stringify(message)}`,
+        `Expected target: ${this.#target}`,
+        `Expected source: ${this.#source}`,
       );
       return;
     }
@@ -126,6 +133,7 @@ export class ChromeRuntimeWriter<Write extends Json> extends BaseWriter<Write> {
   constructor(
     runtime: ChromeRuntime,
     target: ChromeRuntimeStreamTarget,
+    source: ChromeRuntimeStreamTarget,
     onEnd?: OnEnd,
   ) {
     super(
@@ -133,6 +141,7 @@ export class ChromeRuntimeWriter<Write extends Json> extends BaseWriter<Write> {
       async (value: Dispatchable<Write>) => {
         await runtime.sendMessage({
           target,
+          source,
           payload: value,
         });
       },
@@ -172,13 +181,19 @@ export class ChromeRuntimeDuplexStream<
     const reader = new ChromeRuntimeReader<Read>(
       runtime,
       localTarget,
+      remoteTarget,
       async () => {
         await writer.return();
       },
     );
-    writer = new ChromeRuntimeWriter<Write>(runtime, remoteTarget, async () => {
-      await reader.return();
-    });
+    writer = new ChromeRuntimeWriter<Write>(
+      runtime,
+      remoteTarget,
+      localTarget,
+      async () => {
+        await reader.return();
+      },
+    );
     super(reader, writer);
     harden(this);
   }
@@ -188,6 +203,10 @@ export class ChromeRuntimeDuplexStream<
     localTarget: ChromeRuntimeStreamTarget,
     remoteTarget: ChromeRuntimeStreamTarget,
   ): Promise<ChromeRuntimeDuplexStream<Read, Write>> {
+    if (localTarget === remoteTarget) {
+      throw new Error('localTarget and remoteTarget must be different');
+    }
+
     const stream = new ChromeRuntimeDuplexStream<Read, Write>(
       runtime,
       localTarget,