diff --git a/src/web-ui/src/app/components/panels/content-canvas/ContentCanvas.tsx b/src/web-ui/src/app/components/panels/content-canvas/ContentCanvas.tsx
index 1b636c9133..1ba02ece3b 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/ContentCanvas.tsx
+++ b/src/web-ui/src/app/components/panels/content-canvas/ContentCanvas.tsx
@@ -3,7 +3,7 @@
  * Shared content surface. The containing scene or panel owns its layout.
  */
 
-import React, { useCallback, useEffect, useMemo, useRef } from 'react';
+import React, { useCallback, useEffect, useMemo, useRef, useSyncExternalStore } from 'react';
 import { EditorArea } from './editor-area';
 import { AnchorZone } from './anchor-zone';
 import { MissionControl } from './mission-control';
@@ -17,6 +17,7 @@ import { useCurrentWorkspace } from '@/infrastructure/contexts/WorkspaceContext'
 import { openMainSession } from '@/flow_chat/services/sessionActivation';
 import { isSamePath } from '@/shared/utils/pathUtils';
 import './ContentCanvas.scss';
+import { flowChatStore } from '@/flow_chat/store/FlowChatStore';
 export interface ContentCanvasProps {
   /** Workspace path */
   workspacePath?: string;
@@ -71,6 +72,11 @@ export const ContentCanvas: React.FC<ContentCanvasProps> = ({
   const activeBtwSessionTab = useCanvasStore(state => selectActiveBtwSessionTab(state as any));
   const activeBtwSessionData = activeBtwSessionTab?.content.data as BtwSessionPanelData | undefined;
   const { workspace: currentWorkspace } = useCurrentWorkspace();
+  const activeSessionId = useSyncExternalStore(
+    flowChatStore.subscribe.bind(flowChatStore),
+    () => flowChatStore.getState().activeSessionId,
+    () => flowChatStore.getState().activeSessionId,
+  );
   const currentWorkspaceId = currentWorkspace?.id;
   const lastSyncedBtwTabIdRef = useRef<string | null>(null);
   // Initialize hooks
@@ -131,9 +137,10 @@ export const ContentCanvas: React.FC<ContentCanvasProps> = ({
   const hasRenderableTabs = useMemo(() => {
     const groups = [primaryGroup, secondaryGroup, tertiaryGroup];
     return groups.some(group =>
-      group.tabs.some(tab => !tab.isHidden || tab.content.type === 'terminal')
+      group.tabs.some(tab => !tab.isHidden && (tab.content.type !== 'btw-session' || tab.content.data?.parentSessionId === activeSessionId)
+        || tab.content.type === 'terminal')
     );
-  }, [primaryGroup, secondaryGroup, tertiaryGroup]);
+  }, [primaryGroup, secondaryGroup, tertiaryGroup, activeSessionId]);
 
   // Handle anchor close
   const handleAnchorClose = useCallback(() => {
@@ -177,6 +184,7 @@ export const ContentCanvas: React.FC<ContentCanvasProps> = ({
         <div className="canvas-content-canvas__editor" data-openbitfun-component="content-canvas" data-openbitfun-part="editor">
           <EditorArea
             workspacePath={workspacePath}
+            activeSessionId={activeSessionId}
             isSceneActive={isSceneActive}
             onOpenMissionControl={missionControlEnabled ? handleOpenMissionControl : undefined}
             onInteraction={onInteraction}
diff --git a/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorArea.tsx b/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorArea.tsx
index 69642ac999..29a1010baa 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorArea.tsx
+++ b/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorArea.tsx
@@ -10,6 +10,7 @@ import type {
 } from '../types';
 import './EditorArea.scss';
 export interface EditorAreaProps {
+  activeSessionId?: string | null;
   workspacePath?: string;
   isSceneActive?: boolean;
   onOpenMissionControl?: () => void;
@@ -21,6 +22,7 @@ export interface EditorAreaProps {
 }
 
 export const EditorArea: React.FC<EditorAreaProps> = ({
+  activeSessionId,
   workspacePath,
   isSceneActive = true,
   onOpenMissionControl,
@@ -127,6 +129,7 @@ export const EditorArea: React.FC<EditorAreaProps> = ({
   const renderEditorGroup = (groupId: EditorGroupId, group: typeof primaryGroup) => (
     <EditorGroup
       groupId={groupId}
+      activeSessionId={activeSessionId}
       group={group}
       isActive={activeGroupId === groupId}
       isSceneActive={isSceneActive}
diff --git a/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorGroup.tsx b/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorGroup.tsx
index 631ca7d7fc..4b800cd609 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorGroup.tsx
+++ b/src/web-ui/src/app/components/panels/content-canvas/editor-area/EditorGroup.tsx
@@ -28,6 +28,7 @@ import type {
   PanelContent,
   SplitMode,
 } from '../types';
+import { isCanvasTabVisibleForSession } from '../types';
 import './EditorGroup.scss';
 
 function CanvasContentView({ documentId, ...props }: React.ComponentProps<typeof FlexiblePanel> & { documentId: string }) {
@@ -59,6 +60,7 @@ function CanvasContentView({ documentId, ...props }: React.ComponentProps<typeof
 }
 
 export interface EditorGroupProps {
+  activeSessionId?: string | null;
   groupId: EditorGroupId;
   group: EditorGroupState;
   isActive: boolean;
@@ -87,6 +89,7 @@ export interface EditorGroupProps {
 }
 
 export const EditorGroup: React.FC<EditorGroupProps> = ({
+  activeSessionId,
   groupId,
   group,
   isActive,
@@ -115,7 +118,12 @@ export const EditorGroup: React.FC<EditorGroupProps> = ({
 }) => {
   const { t } = useTranslation('components');
   const mode = useContext(CanvasStoreModeContext);
-  const visibleTabs = useMemo(() => group.tabs.filter(t => !t.isHidden), [group.tabs]);
+  const visibleTabs = useMemo(() => group.tabs.filter(t =>
+    !t.isHidden && isCanvasTabVisibleForSession(t, activeSessionId),
+  ), [group.tabs, activeSessionId]);
+  const effectiveActiveTabId = visibleTabs.some(t => t.id === group.activeTabId)
+    ? group.activeTabId
+    : visibleTabs[0]?.id ?? null;
   const activeTabContentRef = useRef<HTMLDivElement | null>(null);
   const activeTabAnimationRef = useRef<Animation | null>(null);
   const previousActiveTabIdRef = useRef(group.activeTabId);
@@ -165,11 +173,11 @@ export const EditorGroup: React.FC<EditorGroupProps> = ({
   // unmounts its transcript while inactive and owns reading state until close.
   const tabsToRender = useMemo(() => {
     const result = group.tabs.filter(t => 
-      (!t.isHidden && (t.content.type === 'btw-session' || t.id === group.activeTabId || cachedTabsRef.current.has(t.id))) ||
+        (!t.isHidden && isCanvasTabVisibleForSession(t, activeSessionId) && (t.content.type === 'btw-session' || t.id === effectiveActiveTabId || cachedTabsRef.current.has(t.id))) ||
       (t.isHidden && isKeepAliveTerminalTab(t))
     );
     return result;
-  }, [group.tabs, group.activeTabId, isKeepAliveTerminalTab]);
+  }, [group.tabs, effectiveActiveTabId, activeSessionId, isKeepAliveTerminalTab]);
 
   const handleContentChange = useCallback((content: PanelContent | null) => {
     if (content && group.activeTabId) {
@@ -239,9 +247,9 @@ export const EditorGroup: React.FC<EditorGroupProps> = ({
     >
       {/* Tab bar */}
       <TabBar
-        tabs={group.tabs}
+        tabs={visibleTabs}
         groupId={groupId}
-        activeTabId={group.activeTabId}
+        activeTabId={effectiveActiveTabId}
         isActiveGroup={isActive}
         onTabClick={handleVisibleTabClick}
         onTabDoubleClick={onTabDoubleClick}
@@ -269,18 +277,18 @@ export const EditorGroup: React.FC<EditorGroupProps> = ({
             tabsToRender.map((tab) => (
               <div
                 key={tab.id}
-                ref={group.activeTabId === tab.id ? activeTabContentRef : undefined}
+                ref={effectiveActiveTabId === tab.id ? activeTabContentRef : undefined}
                 data-openbitfun-component="canvas-editor-group"
                 data-openbitfun-part="tabContent"
                 className="canvas-editor-group__tab-content"
-                style={{ display: group.activeTabId === tab.id ? 'flex' : 'none' }}
+                style={{ display: effectiveActiveTabId === tab.id ? 'flex' : 'none' }}
               >
                 <CanvasContentView
                   documentId={`canvas:${tab.id}`}
                   content={tab.content as any}
-                  isActive={isSceneActive && group.activeTabId === tab.id}
-                  onContentChange={group.activeTabId === tab.id ? handleContentChange : undefined}
-                  onDirtyStateChange={group.activeTabId === tab.id ? handleDirtyStateChange : undefined}
+                  isActive={isSceneActive && effectiveActiveTabId === tab.id}
+                  onContentChange={effectiveActiveTabId === tab.id ? handleContentChange : undefined}
+                  onDirtyStateChange={effectiveActiveTabId === tab.id ? handleDirtyStateChange : undefined}
                   onFileMissingFromDiskChange={
                     onTabFileDeletedFromDiskChange
                       ? (missing) => onTabFileDeletedFromDiskChange(tab.id, missing)
diff --git a/src/web-ui/src/app/components/panels/content-canvas/hooks/canvasPanelOwnership.test.tsx b/src/web-ui/src/app/components/panels/content-canvas/hooks/canvasPanelOwnership.test.tsx
index 00648792a3..1088faa5bc 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/hooks/canvasPanelOwnership.test.tsx
+++ b/src/web-ui/src/app/components/panels/content-canvas/hooks/canvasPanelOwnership.test.tsx
@@ -206,7 +206,7 @@ describe('canvas host panel ownership', () => {
     expect(appManager.getState().layout.rightPanelCollapsed).toBe(true);
   });
 
-  it('preserves manual collapse across content changes, workspace restore and host remount', async () => {
+  it('restores panel visibility when workspace content returns', async () => {
     switchAgentCanvasWorkspace(null, 'workspace-a');
     useAgentCanvasStore.getState().addTab(content('session'), 'active');
     await act(async () => root.render(<Hosts />));
@@ -222,10 +222,10 @@ describe('canvas host panel ownership', () => {
       root.render(<Hosts />);
     });
     expect(useAgentCanvasStore.getState().primaryGroup.tabs).toHaveLength(1);
-    expect(appManager.getState().layout.rightPanelCollapsed).toBe(true);
+    expect(appManager.getState().layout.rightPanelCollapsed).toBe(false);
     await act(async () => root.render(null));
     await act(async () => root.render(<Hosts />));
-    expect(appManager.getState().layout.rightPanelCollapsed).toBe(true);
+    expect(appManager.getState().layout.rightPanelCollapsed).toBe(false);
   });
 
   it('keeps an explicitly opened empty panel and counts all editor groups when closing', async () => {
@@ -245,7 +245,7 @@ describe('canvas host panel ownership', () => {
     expect(appManager.getState().layout.rightPanelCollapsed).toBe(true);
   });
 
-  it('preserves an open panel when workspace snapshots change before the shell rerenders', async () => {
+  it('collapses when a workspace snapshot has no visible content before the shell rerenders', async () => {
     switchAgentCanvasWorkspace(null, 'workspace-a');
     useAgentCanvasStore.getState().addTab(content('workspace-a'), 'active');
     appManager.updateLayout({ rightPanelCollapsed: false });
@@ -253,7 +253,7 @@ describe('canvas host panel ownership', () => {
     await act(async () => switchAgentCanvasWorkspace('workspace-a', 'workspace-b'));
     expect(useAgentCanvasStore.getState().workspaceKey).toBe('workspace-b');
     expect(useAgentCanvasStore.getState().primaryGroup.tabs).toHaveLength(0);
-    expect(appManager.getState().layout.rightPanelCollapsed).toBe(false);
+    expect(appManager.getState().layout.rightPanelCollapsed).toBe(true);
     await act(async () => switchAgentCanvasWorkspace('workspace-b', 'workspace-a'));
     expect(useAgentCanvasStore.getState().primaryGroup.tabs).toHaveLength(1);
     expect(appManager.getState().layout.rightPanelCollapsed).toBe(false);
diff --git a/src/web-ui/src/app/components/panels/content-canvas/hooks/usePanelTabCoordinator.ts b/src/web-ui/src/app/components/panels/content-canvas/hooks/usePanelTabCoordinator.ts
index 6a1449a19d..6524c92a7f 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/hooks/usePanelTabCoordinator.ts
+++ b/src/web-ui/src/app/components/panels/content-canvas/hooks/usePanelTabCoordinator.ts
@@ -2,7 +2,6 @@ import { useEffect, useRef } from 'react';
 
 interface UsePanelTabCoordinatorOptions {
   visibleTabCount: number;
-  /** Changing workspace restores content without changing the user's layout. */
   scopeKey?: string;
   expandEventName: string;
   onExpand: () => void;
@@ -27,13 +26,18 @@ export function usePanelTabCoordinator({
     const previous = previousRef.current;
     previousRef.current = { visibleTabCount, scopeKey };
     if (
-      previous.scopeKey === scopeKey
-      && previous.visibleTabCount > 0
+      previous.visibleTabCount > 0
       && visibleTabCount === 0
     ) {
       onCollapse();
+    } else if (
+      previous.visibleTabCount === 0
+      && visibleTabCount > 0
+      && previous.scopeKey !== undefined
+    ) {
+      onExpand();
     }
-  }, [visibleTabCount, scopeKey, onCollapse]);
+  }, [visibleTabCount, scopeKey, onExpand, onCollapse]);
 
   // Compatibility for callers that explicitly request this panel, including
   // actions that reveal an existing tab without creating another one.
diff --git a/src/web-ui/src/app/components/panels/content-canvas/types/content.ts b/src/web-ui/src/app/components/panels/content-canvas/types/content.ts
index 9429f961d7..f75d0d59dd 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/types/content.ts
+++ b/src/web-ui/src/app/components/panels/content-canvas/types/content.ts
@@ -5,6 +5,17 @@
 
 export type { PanelContentType, PanelContent } from '../../base/types';
 import type { PanelContentType } from '../../base/types';
+import type { CanvasTab } from './tab';
+
+/** BTW and subagent tabs are scoped to the primary session that opened them. */
+export const isCanvasTabVisibleForSession = (
+  tab: Pick<CanvasTab, 'content'>,
+  activeSessionId?: string | null,
+): boolean => {
+  if (tab.content.type !== 'btw-session') return true;
+  const parentSessionId = tab.content.data?.parentSessionId;
+  return Boolean(activeSessionId && parentSessionId === activeSessionId);
+};
 
 /**
  * File viewer types (code, markdown, images, etc.).
diff --git a/src/web-ui/src/app/components/panels/content-canvas/types/index.ts b/src/web-ui/src/app/components/panels/content-canvas/types/index.ts
index 33d29edba7..6f1706e779 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/types/index.ts
+++ b/src/web-ui/src/app/components/panels/content-canvas/types/index.ts
@@ -46,5 +46,6 @@ export type {
 export {
   FILE_VIEWER_TYPES,
   isFileViewerType,
+  isCanvasTabVisibleForSession,
   TAB_EVENTS,
 } from './content';
diff --git a/src/web-ui/src/app/scenes/session/AuxPane.tsx b/src/web-ui/src/app/scenes/session/AuxPane.tsx
index fbd604d32c..0f85b30514 100644
--- a/src/web-ui/src/app/scenes/session/AuxPane.tsx
+++ b/src/web-ui/src/app/scenes/session/AuxPane.tsx
@@ -5,7 +5,7 @@
  * Renamed from panels/ContentPanel. All logic preserved.
  */
 
-import { forwardRef, useEffect, useRef, useImperativeHandle, useCallback } from 'react';
+import { forwardRef, useEffect, useRef, useImperativeHandle, useCallback, useSyncExternalStore } from 'react';
 import { ContentCanvas, useCanvasStore } from '../../components/panels/content-canvas';
 import { usePanelTabCoordinator } from '../../components/panels/content-canvas/hooks/usePanelTabCoordinator';
 import { TAB_EVENTS } from '../../components/panels/content-canvas/types';
@@ -20,6 +20,8 @@ import { useI18n } from '@/infrastructure/i18n';
 import type { PanelContent as OldPanelContent } from '../../components/panels/base/types';
 import type { PanelContent } from '../../components/panels/content-canvas/types';
 import { createLogger } from '@/shared/utils/logger';
+import { flowChatStore } from '@/flow_chat/store/FlowChatStore';
+import { isCanvasTabVisibleForSession } from '../../components/panels/content-canvas/types';
 
 import './AuxPane.scss';
 
@@ -44,6 +46,11 @@ const AuxPane = forwardRef<AuxPaneRef, AuxPaneProps>(
     const { t } = useI18n('components');
     const { workspace } = useCurrentWorkspace();
     const workspaceId = workspace?.id;
+    const activeSessionId = useSyncExternalStore(
+      flowChatStore.subscribe.bind(flowChatStore),
+      () => flowChatStore.getState().activeSessionId,
+      () => flowChatStore.getState().activeSessionId,
+    );
 
     // Fine-grained selectors so unrelated store changes do not re-render.
     const addTab = useCanvasStore(state => state.addTab);
@@ -57,7 +64,9 @@ const AuxPane = forwardRef<AuxPaneRef, AuxPaneProps>(
     const canvasWorkspaceKey = useCanvasStore(state => state.workspaceKey);
     const { expandPanel, collapsePanel } = usePanelTabCoordinator({
       visibleTabCount: [primaryGroup, secondaryGroup, tertiaryGroup]
-        .reduce((count, group) => count + group.tabs.filter(tab => !tab.isHidden).length, 0),
+        .reduce((count, group) => count + group.tabs.filter(tab =>
+          !tab.isHidden && isCanvasTabVisibleForSession(tab, activeSessionId),
+        ).length, 0),
       scopeKey: canvasWorkspaceKey,
       expandEventName: TAB_EVENTS.EXPAND_RIGHT_PANEL,
       onExpand: expandSessionAuxPane,