diff --git a/src/main/runtime/rpc/relay-transport.test.ts b/src/main/runtime/rpc/relay-transport.test.ts
index 360a13fab34..e1f2d7fa76f 100644
--- a/src/main/runtime/rpc/relay-transport.test.ts
+++ b/src/main/runtime/rpc/relay-transport.test.ts
@@ -109,7 +109,11 @@ describe('CloudRelayTransport', () => {
         )
       }
       const emit = (event: string, ...args: unknown[]): void => {
-        for (const fn of listeners.get(event) ?? []) {
+        const eventListeners = listeners.get(event) ?? []
+        if (event === 'error' && eventListeners.length === 0) {
+          throw args[0]
+        }
+        for (const fn of eventListeners) {
           fn(...args)
         }
       }
@@ -122,7 +126,7 @@ describe('CloudRelayTransport', () => {
         on: addListener,
         once: addListener,
         off: removeListener,
-        send: () => {},
+        send: vi.fn(),
         terminate: () => {}
       }
       const onConnectionClosed = vi.fn()
@@ -133,6 +137,13 @@ describe('CloudRelayTransport', () => {
         createSocket: () => fakeSocket as unknown as WebSocketClient,
         onConnectionClosed
       })
+      let reply: ((response: string) => void) | null = null
+      const onMessage = vi.fn(
+        (_message: string | Uint8Array<ArrayBufferLike>, respond: (response: string) => void) => {
+          reply = respond
+        }
+      )
+      transport.onMessage(onMessage)
       const opening = transport.openConnection({
         connId: 'conn-1',
         connTicket: 'ticket-1',
@@ -142,11 +153,16 @@ describe('CloudRelayTransport', () => {
       })
       emit('open')
       await opening
+      vi.mocked(fakeSocket.send).mockClear()
+      emit('message', 'before-stop', false)
+      expect(onMessage).toHaveBeenCalledOnce()
 
       let stopped = false
       const stopPromise = transport.stop().then(() => {
         stopped = true
       })
+      emit('message', 'during-stop', false)
+      expect(onMessage).toHaveBeenCalledOnce()
       await vi.advanceTimersByTimeAsync(4_999)
       expect(stopped).toBe(false)
       await vi.advanceTimersByTimeAsync(1)
@@ -165,6 +181,14 @@ describe('CloudRelayTransport', () => {
       // late frames must not reach wiring after their metadata was released.
       expect(() => emit('message', 'late-after-stop', false)).not.toThrow()
       expect(onLateMessage).not.toHaveBeenCalled()
+      expect(reply).not.toBeNull()
+      await transport.start()
+      reply!('late-reply')
+      expect(fakeSocket.send).not.toHaveBeenCalled()
+      expect(() => emit('error', new Error('late socket failure'))).not.toThrow()
+      emit('close')
+      expect(listeners.get('error')).toHaveLength(0)
+      expect(listeners.get('close')).toHaveLength(0)
       expect(() => transport.setGeneration(2)).not.toThrow()
     } finally {
       vi.useRealTimers()
diff --git a/src/main/runtime/rpc/relay-transport.ts b/src/main/runtime/rpc/relay-transport.ts
index a96f65fd355..fdb7e50a20f 100644
--- a/src/main/runtime/rpc/relay-transport.ts
+++ b/src/main/runtime/rpc/relay-transport.ts
@@ -163,6 +163,9 @@ export class CloudRelayTransport implements RpcTransport, MobileSocketTransport
         this.finalizeConnection(connection.connId, socket)
       }
       const onMessage = (raw: RawData, isBinary: boolean): void => {
+        if (this.stopped || finalized) {
+          return
+        }
         if (!attached) {
           attached = true
           clearTimeout(deadline)
@@ -173,7 +176,7 @@ export class CloudRelayTransport implements RpcTransport, MobileSocketTransport
         this.messageHandler?.(
           message,
           (response) => {
-            if (socket.readyState === socket.OPEN) {
+            if (!this.stopped && !finalized && socket.readyState === socket.OPEN) {
               socket.send(response)
             }
           },
@@ -203,6 +206,7 @@ export class CloudRelayTransport implements RpcTransport, MobileSocketTransport
         }
       }
       this.detachListenersBySocket.set(socket, () => {
+        finalized = true
         socket.off('message', onMessage)
         socket.off('open', onOpen)
         socket.off('error', onError)
@@ -236,6 +240,7 @@ export class CloudRelayTransport implements RpcTransport, MobileSocketTransport
         if (connectionId) {
           this.finalizeConnection(connectionId, socket)
         }
+        this.quarantineDetachedSocket(socket)
         resolve()
       }, RELAY_SOCKET_CLOSE_TIMEOUT_MS)
       socket.once('close', onClose)
@@ -250,6 +255,20 @@ export class CloudRelayTransport implements RpcTransport, MobileSocketTransport
     return metadata?.transport === 'relay' ? metadata.basisConnId : undefined
   }
 
+  private quarantineDetachedSocket(socket: WebSocket): void {
+    if (socket.readyState === socket.CLOSED) {
+      return
+    }
+    // Why: forced cleanup can precede ws's terminal error/close event.
+    const swallowLateError = (): void => {}
+    const clearQuarantine = (): void => {
+      socket.off('error', swallowLateError)
+      socket.off('close', clearQuarantine)
+    }
+    socket.on('error', swallowLateError)
+    socket.once('close', clearQuarantine)
+  }
+
   private finalizeConnection(connectionId: string, socket: WebSocket): void {
     if (this.socketsByConnectionId.get(connectionId) !== socket) {
       return