diff --git a/apps/desktop/src/app/session/hooks/use-message-stream.ts b/apps/desktop/src/app/session/hooks/use-message-stream.ts
index 3ee52ec8eb7d..99330d997d13 100644
--- a/apps/desktop/src/app/session/hooks/use-message-stream.ts
+++ b/apps/desktop/src/app/session/hooks/use-message-stream.ts
@@ -17,7 +17,7 @@ import {
 } from '@/lib/chat-messages'
 import { coerceGatewayText, coerceThinkingText, normalizePersonalityValue } from '@/lib/chat-runtime'
 import { playCompletionSound } from '@/lib/completion-sound'
-import { gatewayEventRequiresSessionId } from '@/lib/gateway-events'
+import { resolveGatewayEventSessionId } from '@/lib/gateway-events'
 import {
   dedupeGeneratedImageEchoesInParts,
   generatedImageEchoSources,
@@ -262,6 +262,8 @@ export function useMessageStream({
   sessionStateByRuntimeIdRef,
   updateSessionState
 }: MessageStreamOptions) {
+  const unscopedStreamSessionIdRef = useRef<string | null>(null)
+
   const sessionInterrupted = useCallback(
     (sessionId: string) => sessionStateByRuntimeIdRef.current.get(sessionId)?.interrupted ?? false,
     [sessionStateByRuntimeIdRef]
@@ -715,11 +717,20 @@ export function useMessageStream({
       const payload = event.payload as GatewayEventPayload | undefined
       const explicitSid = event.session_id || ''
 
-      if (!explicitSid && gatewayEventRequiresSessionId(event.type)) {
+      const route = resolveGatewayEventSessionId({
+        activeSessionId: activeSessionIdRef.current,
+        eventType: event.type,
+        explicitSessionId: explicitSid,
+        unscopedStreamSessionId: unscopedStreamSessionIdRef.current
+      })
+
+      unscopedStreamSessionIdRef.current = route.nextUnscopedStreamSessionId
+
+      if (route.drop) {
         return
       }
 
-      const sessionId = explicitSid || activeSessionIdRef.current
+      const sessionId = route.sessionId
       const isActiveEvent = !!sessionId && sessionId === activeSessionIdRef.current
 
       if (event.type === 'gateway.ready') {
diff --git a/apps/desktop/src/lib/gateway-events.test.ts b/apps/desktop/src/lib/gateway-events.test.ts
index d51a943611f0..7435d22d6ee4 100644
--- a/apps/desktop/src/lib/gateway-events.test.ts
+++ b/apps/desktop/src/lib/gateway-events.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { gatewayEventRequiresSessionId } from './gateway-events'
+import { gatewayEventRequiresSessionId, resolveGatewayEventSessionId } from './gateway-events'
 
 describe('gateway event routing', () => {
   it('drops only unscoped subagent events (genuinely background work)', () => {
@@ -24,4 +24,75 @@ describe('gateway event routing', () => {
     expect(gatewayEventRequiresSessionId('session.info')).toBe(false)
     expect(gatewayEventRequiresSessionId(undefined)).toBe(false)
   })
+
+  it('keeps unscoped stream events pinned to the session that started them', () => {
+    const started = resolveGatewayEventSessionId({
+      activeSessionId: 'session-a',
+      eventType: 'message.start',
+      explicitSessionId: '',
+      unscopedStreamSessionId: null
+    })
+
+    expect(started).toEqual({
+      drop: false,
+      nextUnscopedStreamSessionId: 'session-a',
+      sessionId: 'session-a'
+    })
+
+    const delta = resolveGatewayEventSessionId({
+      activeSessionId: 'session-b',
+      eventType: 'message.delta',
+      explicitSessionId: '',
+      unscopedStreamSessionId: started.nextUnscopedStreamSessionId
+    })
+
+    expect(delta).toEqual({
+      drop: false,
+      nextUnscopedStreamSessionId: 'session-a',
+      sessionId: 'session-a'
+    })
+
+    const completed = resolveGatewayEventSessionId({
+      activeSessionId: 'session-b',
+      eventType: 'message.complete',
+      explicitSessionId: '',
+      unscopedStreamSessionId: delta.nextUnscopedStreamSessionId
+    })
+
+    expect(completed).toEqual({
+      drop: false,
+      nextUnscopedStreamSessionId: null,
+      sessionId: 'session-a'
+    })
+  })
+
+  it('routes a new unscoped stream start to the currently active session', () => {
+    const routed = resolveGatewayEventSessionId({
+      activeSessionId: 'session-b',
+      eventType: 'message.start',
+      explicitSessionId: '',
+      unscopedStreamSessionId: 'session-a'
+    })
+
+    expect(routed).toEqual({
+      drop: false,
+      nextUnscopedStreamSessionId: 'session-b',
+      sessionId: 'session-b'
+    })
+  })
+
+  it('keeps explicit events scoped and clears a matching pinned stream on completion', () => {
+    const routed = resolveGatewayEventSessionId({
+      activeSessionId: 'session-b',
+      eventType: 'message.complete',
+      explicitSessionId: 'session-a',
+      unscopedStreamSessionId: 'session-a'
+    })
+
+    expect(routed).toEqual({
+      drop: false,
+      nextUnscopedStreamSessionId: null,
+      sessionId: 'session-a'
+    })
+  })
 })
diff --git a/apps/desktop/src/lib/gateway-events.ts b/apps/desktop/src/lib/gateway-events.ts
index 673d1df8c6d6..d3f0e30999ee 100644
--- a/apps/desktop/src/lib/gateway-events.ts
+++ b/apps/desktop/src/lib/gateway-events.ts
@@ -11,6 +11,28 @@ function asRecord(payload: unknown): Record<string, unknown> {
   return payload && typeof payload === 'object' ? (payload as Record<string, unknown>) : {}
 }
 
+const UNSCOPED_STREAM_EVENT_TYPES = new Set([
+  'approval.request',
+  'browser.progress',
+  'clarify.request',
+  'error',
+  'message.complete',
+  'message.delta',
+  'message.start',
+  'reasoning.available',
+  'reasoning.delta',
+  'secret.request',
+  'status.update',
+  'sudo.request',
+  'thinking.delta',
+  'tool.complete',
+  'tool.generating',
+  'tool.progress',
+  'tool.start'
+])
+
+const UNSCOPED_STREAM_END_EVENT_TYPES = new Set(['error', 'message.complete'])
+
 /**
  * Whether an unscoped event (no `session_id`) must be dropped rather than
  * attributed to the focused chat.
@@ -27,6 +49,63 @@ export function gatewayEventRequiresSessionId(eventType: string | undefined): bo
   return eventType?.startsWith('subagent.') ?? false
 }
 
+export interface GatewayEventSessionRouteInput {
+  activeSessionId: null | string
+  eventType: string | undefined
+  explicitSessionId: string
+  unscopedStreamSessionId: null | string
+}
+
+export interface GatewayEventSessionRoute {
+  drop: boolean
+  nextUnscopedStreamSessionId: null | string
+  sessionId: null | string
+}
+
+export function resolveGatewayEventSessionId({
+  activeSessionId,
+  eventType,
+  explicitSessionId,
+  unscopedStreamSessionId
+}: GatewayEventSessionRouteInput): GatewayEventSessionRoute {
+  if (explicitSessionId) {
+    const nextUnscopedStreamSessionId =
+      eventType && UNSCOPED_STREAM_END_EVENT_TYPES.has(eventType) && explicitSessionId === unscopedStreamSessionId
+        ? null
+        : unscopedStreamSessionId
+
+    return {
+      drop: false,
+      nextUnscopedStreamSessionId,
+      sessionId: explicitSessionId
+    }
+  }
+
+  if (gatewayEventRequiresSessionId(eventType)) {
+    return {
+      drop: true,
+      nextUnscopedStreamSessionId: unscopedStreamSessionId,
+      sessionId: null
+    }
+  }
+
+  const streamEvent = eventType ? UNSCOPED_STREAM_EVENT_TYPES.has(eventType) : false
+  const sessionId = eventType === 'message.start' ? activeSessionId : streamEvent ? unscopedStreamSessionId || activeSessionId : activeSessionId
+  let nextUnscopedStreamSessionId = unscopedStreamSessionId
+
+  if (eventType === 'message.start' && activeSessionId) {
+    nextUnscopedStreamSessionId = activeSessionId
+  } else if (eventType && UNSCOPED_STREAM_END_EVENT_TYPES.has(eventType)) {
+    nextUnscopedStreamSessionId = null
+  }
+
+  return {
+    drop: false,
+    nextUnscopedStreamSessionId,
+    sessionId
+  }
+}
+
 export function gatewayEventCompletedFileDiff(event: RpcEventLike): boolean {
   if (event.type !== 'tool.complete') {
     return false