diff --git a/src/renderer/src/lib/file-preview.test.ts b/src/renderer/src/lib/file-preview.test.ts
index bea6e40a3be..23df643b51b 100644
--- a/src/renderer/src/lib/file-preview.test.ts
+++ b/src/renderer/src/lib/file-preview.test.ts
@@ -2,18 +2,33 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import {
   REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE,
   getWorkspaceFileBrowserOpenTarget,
-  openFileInBrowserTab
+  openFileInBrowserTab,
+  openFilePreviewToSide
 } from './file-preview'
 
 const mocks = vi.hoisted(() => ({
   createBrowserTab: vi.fn(),
+  createEmptySplitGroup: vi.fn(() => 'group-2'),
+  createWebRuntimeSessionBrowserTab: vi.fn(),
+  environmentId: null as string | null,
   connectionId: null as string | null
 }))
 
+vi.mock('@/lib/worktree-runtime-owner', () => ({
+  getRuntimeEnvironmentIdForWorktree: () => mocks.environmentId
+}))
+
+vi.mock('@/runtime/web-runtime-session', () => ({
+  createWebRuntimeSessionBrowserTab: mocks.createWebRuntimeSessionBrowserTab
+}))
+
 vi.mock('@/store', () => ({
   useAppStore: {
     getState: () => ({
       createBrowserTab: mocks.createBrowserTab,
+      createEmptySplitGroup: mocks.createEmptySplitGroup,
+      groupsByWorktree: {},
+      layoutByWorktree: {},
       repos: [{ id: 'repo-1', connectionId: mocks.connectionId }],
       worktreesByRepo: {
         'repo-1': [{ id: 'wt-1', repoId: 'repo-1' }]
@@ -24,6 +39,8 @@ vi.mock('@/store', () => ({
 
 beforeEach(() => {
   vi.clearAllMocks()
+  mocks.createWebRuntimeSessionBrowserTab.mockResolvedValue(true)
+  mocks.environmentId = null
   mocks.connectionId = null
 })
 
@@ -40,6 +57,43 @@ describe('openFileInBrowserTab', () => {
     })
   })
 
+  it('creates paired-runtime file browsers at the owning host', () => {
+    mocks.environmentId = 'runtime-1'
+
+    openFileInBrowserTab({ filePath: '/srv/repo/example.html', worktreeId: 'wt-1' })
+
+    expect(mocks.createWebRuntimeSessionBrowserTab).toHaveBeenCalledWith({
+      worktreeId: 'wt-1',
+      environmentId: 'runtime-1',
+      url: 'file:///srv/repo/example.html',
+      stagedTitle: 'example.html',
+      stagedFocusAddressBar: false
+    })
+    expect(mocks.createBrowserTab).not.toHaveBeenCalled()
+  })
+
+  it('creates paired-runtime side previews in the requested split', () => {
+    mocks.environmentId = 'runtime-1'
+
+    openFilePreviewToSide({
+      language: 'html',
+      filePath: '/srv/repo/example.html',
+      worktreeId: 'wt-1',
+      sourceGroupId: 'group-1'
+    })
+
+    expect(mocks.createWebRuntimeSessionBrowserTab).toHaveBeenCalledWith({
+      worktreeId: 'wt-1',
+      environmentId: 'runtime-1',
+      url: 'file:///srv/repo/example.html',
+      clientTargetGroupId: 'group-2',
+      clientTargetGroupCreated: true,
+      stagedTitle: 'example.html',
+      stagedFocusAddressBar: false
+    })
+    expect(mocks.createBrowserTab).not.toHaveBeenCalled()
+  })
+
   it('returns unsupported for SSH worktrees without creating a local file URL tab', () => {
     mocks.connectionId = 'ssh-1'
 
diff --git a/src/renderer/src/lib/file-preview.ts b/src/renderer/src/lib/file-preview.ts
index fc23d680ad1..99cd8b56357 100644
--- a/src/renderer/src/lib/file-preview.ts
+++ b/src/renderer/src/lib/file-preview.ts
@@ -1,12 +1,23 @@
 import { toast } from 'sonner'
 import { absolutePathToFileUri } from '@/components/editor/markdown-internal-links'
 import { getConnectionId } from '@/lib/connection-context'
+import { getRuntimeEnvironmentIdForWorktree } from '@/lib/worktree-runtime-owner'
+import { createWebRuntimeSessionBrowserTab } from '@/runtime/web-runtime-session'
 import { useAppStore } from '@/store'
 import { findSiblingGroupId } from '@/store/slices/tabs'
 
 export type PreviewableLanguage = 'html'
 export const REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE =
   'Open in Orca Browser is only available for local files.'
+const FILE_BROWSER_OPEN_FAILED_MESSAGE = 'Unable to open this file in Orca Browser.'
+
+function reportRemoteFileBrowserOpen(result: Promise<boolean>): void {
+  void result.then((created) => {
+    if (!created) {
+      toast.error(FILE_BROWSER_OPEN_FAILED_MESSAGE)
+    }
+  })
+}
 
 export type WorkspaceFileBrowserOpenTarget =
   | {
@@ -51,6 +62,19 @@ export function openFileInBrowserTab(params: {
   }
 
   const state = useAppStore.getState()
+  const environmentId = getRuntimeEnvironmentIdForWorktree(state, params.worktreeId)
+  if (environmentId) {
+    reportRemoteFileBrowserOpen(
+      createWebRuntimeSessionBrowserTab({
+        worktreeId: params.worktreeId,
+        environmentId,
+        url: target.url,
+        stagedTitle: target.title,
+        stagedFocusAddressBar: false
+      })
+    )
+    return target
+  }
 
   state.createBrowserTab(params.worktreeId, target.url, {
     title: target.title,
@@ -114,6 +138,22 @@ export function openFilePreviewToSide(params: {
     return
   }
 
+  const environmentId = getRuntimeEnvironmentIdForWorktree(state, worktreeId)
+  if (environmentId) {
+    reportRemoteFileBrowserOpen(
+      createWebRuntimeSessionBrowserTab({
+        worktreeId,
+        environmentId,
+        url: target.url,
+        clientTargetGroupId: targetGroupId,
+        clientTargetGroupCreated: !existingSibling,
+        stagedTitle: target.title,
+        stagedFocusAddressBar: false
+      })
+    )
+    return
+  }
+
   state.createBrowserTab(worktreeId, target.url, {
     title: target.title,
     targetGroupId,
diff --git a/src/renderer/src/runtime/web-runtime-session.test.ts b/src/renderer/src/runtime/web-runtime-session.test.ts
index 71ecd304f96..e4cc677406d 100644
--- a/src/renderer/src/runtime/web-runtime-session.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session.test.ts
@@ -34,12 +34,18 @@ import {
   resetWebAgentSessionHandoffsForTests
 } from './web-agent-session-handoff'
 import { toRuntimeExecutionHostId } from '../../../shared/execution-host'
+import {
+  isWebSessionBrowserPlacementGroupReserved,
+  resetWebSessionBrowserPlacementsForTests
+} from './web-session-browser-placement'
 
 const mocks = vi.hoisted(() => ({
   getState: vi.fn(),
   setState: vi.fn(),
   setActiveWorktree: vi.fn(),
   createBrowserTab: vi.fn(),
+  closeEmptyGroup: vi.fn(),
+  moveUnifiedTabToGroup: vi.fn(),
   setRemoteBrowserPageHandle: vi.fn(),
   focusBrowserTabInWorktree: vi.fn(),
   applyFreshWebSessionTabsSnapshot: vi.fn(),
@@ -252,7 +258,10 @@ describe('createWebRuntimeSessionBrowserTab', () => {
       activeWorktreeId: WORKTREE_ID,
       browserPagesByWorkspace: {},
       remoteBrowserPageHandlesByPageId: {},
+      unifiedTabsByWorktree: {},
       createBrowserTab: mocks.createBrowserTab,
+      closeEmptyGroup: mocks.closeEmptyGroup,
+      moveUnifiedTabToGroup: mocks.moveUnifiedTabToGroup,
       setRemoteBrowserPageHandle: mocks.setRemoteBrowserPageHandle,
       focusBrowserTabInWorktree: mocks.focusBrowserTabInWorktree,
       setActiveWorktree: mocks.setActiveWorktree
@@ -268,6 +277,7 @@ describe('createWebRuntimeSessionBrowserTab', () => {
       activePageId: 'local-page-1',
       pageIds: ['local-page-1']
     })
+    mocks.moveUnifiedTabToGroup.mockReturnValue(true)
     mocks.applyFreshWebSessionTabsSnapshot.mockReturnValue({ state: 'after' })
     mocks.resolveHostSessionTabIdForWebSessionTab.mockReturnValue(null)
     mocks.deliverLaunchPromptToAgentTab.mockResolvedValue(true)
@@ -276,6 +286,7 @@ describe('createWebRuntimeSessionBrowserTab', () => {
   afterEach(() => {
     vi.unstubAllGlobals()
     clearRuntimeCompatibilityCacheForTests()
+    resetWebSessionBrowserPlacementsForTests()
     vi.clearAllMocks()
   })
 
@@ -350,6 +361,86 @@ describe('createWebRuntimeSessionBrowserTab', () => {
     })
   })
 
+  it('keeps the requested split reserved until a pre-published browser gains a unified tab', async () => {
+    mocks.getState.mockReturnValue({
+      settings: { activeRuntimeEnvironmentId: ENVIRONMENT_ID },
+      activeWorktreeId: WORKTREE_ID,
+      browserPagesByWorkspace: {
+        'host-browser-workspace': [
+          { id: 'host-browser-page', workspaceId: 'host-browser-workspace' }
+        ]
+      },
+      remoteBrowserPageHandlesByPageId: {
+        'host-browser-page': {
+          environmentId: ENVIRONMENT_ID,
+          remotePageId: 'remote-browser-page-1'
+        }
+      },
+      unifiedTabsByWorktree: { [WORKTREE_ID]: [] },
+      createBrowserTab: mocks.createBrowserTab,
+      closeEmptyGroup: mocks.closeEmptyGroup,
+      moveUnifiedTabToGroup: mocks.moveUnifiedTabToGroup,
+      setRemoteBrowserPageHandle: mocks.setRemoteBrowserPageHandle,
+      focusBrowserTabInWorktree: mocks.focusBrowserTabInWorktree,
+      setActiveWorktree: mocks.setActiveWorktree
+    })
+    const runtimeCall = vi
+      .fn()
+      .mockResolvedValueOnce({
+        id: 'create',
+        ok: true,
+        result: { browserPageId: 'remote-browser-page-1' }
+      })
+      .mockResolvedValueOnce({ id: 'list', ok: true, result: makeSnapshot() })
+    vi.stubGlobal('window', { api: { runtimeEnvironments: { call: runtimeCall } } })
+
+    await expect(
+      createWebRuntimeSessionBrowserTab({
+        worktreeId: WORKTREE_ID,
+        environmentId: ENVIRONMENT_ID,
+        clientTargetGroupId: 'client-preview-group'
+      })
+    ).resolves.toBe(true)
+
+    expect(
+      isWebSessionBrowserPlacementGroupReserved({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        groupId: 'client-preview-group'
+      })
+    ).toBe(true)
+    expect(mocks.createBrowserTab).not.toHaveBeenCalled()
+    expect(mocks.closeEmptyGroup).not.toHaveBeenCalled()
+  })
+
+  it('releases and removes a newly-created split when host creation fails', async () => {
+    vi.stubGlobal('window', {
+      api: {
+        runtimeEnvironments: {
+          call: vi.fn().mockRejectedValue(new Error('offline'))
+        }
+      }
+    })
+
+    await expect(
+      createWebRuntimeSessionBrowserTab({
+        worktreeId: WORKTREE_ID,
+        environmentId: ENVIRONMENT_ID,
+        clientTargetGroupId: 'client-preview-group',
+        clientTargetGroupCreated: true
+      })
+    ).resolves.toBe(false)
+
+    expect(mocks.closeEmptyGroup).toHaveBeenCalledWith(WORKTREE_ID, 'client-preview-group')
+    expect(
+      isWebSessionBrowserPlacementGroupReserved({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        groupId: 'client-preview-group'
+      })
+    ).toBe(false)
+  })
+
   it('keeps the requested worktree selected while the browser snapshot catches up', async () => {
     const snapshot = makeSnapshot()
     const setStateResults: unknown[] = []
diff --git a/src/renderer/src/runtime/web-runtime-session.ts b/src/renderer/src/runtime/web-runtime-session.ts
index afe64a8097e..efd30bd3756 100644
--- a/src/renderer/src/runtime/web-runtime-session.ts
+++ b/src/renderer/src/runtime/web-runtime-session.ts
@@ -36,7 +36,10 @@ import {
 } from './agent-session-create-operation'
 import { parseRemoteRuntimePtyId } from './runtime-terminal-stream'
 import { toRuntimeWorktreeSelector } from './runtime-worktree-selector'
-import { recordWebSessionFocusIntent } from './web-session-focus-intent'
+import {
+  clearWebSessionFocusIntentIfMatches,
+  recordWebSessionFocusIntent
+} from './web-session-focus-intent'
 import { clearWebSessionCloseIntent, recordWebSessionCloseIntent } from './web-session-close-intent'
 import {
   clearWebSessionReorderIntent,
@@ -61,6 +64,11 @@ import { translate } from '../i18n/i18n'
 import { getRuntimeEnvironmentRevision } from './runtime-environment-revision'
 import { parsePaneKey } from '../../../shared/stable-pane-id'
 import { toRuntimeExecutionHostId } from '../../../shared/execution-host'
+import {
+  recordWebSessionBrowserPlacement,
+  releaseWebSessionBrowserPlacementGroup,
+  reserveWebSessionBrowserPlacementGroup
+} from './web-session-browser-placement'
 
 export {
   HOST_TERMINAL_SURFACE_SEPARATOR,
@@ -423,6 +431,8 @@ export async function createWebRuntimeSessionBrowserTab(args: {
   url?: string
   profileId?: string | null
   targetGroupId?: string
+  clientTargetGroupId?: string
+  clientTargetGroupCreated?: boolean
   selectWorktree?: boolean
   stagedTitle?: string
   stagedFocusAddressBar?: boolean
@@ -440,6 +450,13 @@ export async function createWebRuntimeSessionBrowserTab(args: {
 
   const shouldSelectWorktree = args.selectWorktree !== false
   const stagedFromWorktreeId = useAppStore.getState().activeWorktreeId
+  if (args.clientTargetGroupId) {
+    reserveWebSessionBrowserPlacementGroup({
+      environmentId,
+      worktreeId: args.worktreeId,
+      groupId: args.clientTargetGroupId
+    })
+  }
   if (shouldSelectWorktree) {
     selectWebRuntimeSessionWorktree(args.worktreeId, environmentId)
   }
@@ -464,12 +481,20 @@ export async function createWebRuntimeSessionBrowserTab(args: {
     if (matchesWebSessionIntentOwner(intentOwner)) {
       recordWebSessionFocusIntent(intentOwner, args.worktreeId, created.browserPageId)
     }
-    stageWebRuntimeBrowserTab({
+    if (args.clientTargetGroupId) {
+      recordWebSessionBrowserPlacement({
+        environmentId,
+        worktreeId: args.worktreeId,
+        remotePageId: created.browserPageId,
+        groupId: args.clientTargetGroupId
+      })
+    }
+    const staged = stageWebRuntimeBrowserTab({
       environmentId,
       worktreeId: args.worktreeId,
       remotePageId: created.browserPageId,
       url: args.url,
-      targetGroupId: args.targetGroupId,
+      targetGroupId: args.clientTargetGroupId ?? args.targetGroupId,
       title: args.stagedTitle,
       focusAddressBar: args.stagedFocusAddressBar,
       restoreFocus:
@@ -477,11 +502,53 @@ export async function createWebRuntimeSessionBrowserTab(args: {
         (stagedFromWorktreeId === args.worktreeId ||
           useAppStore.getState().activeWorktreeId === args.worktreeId)
     })
-    void refreshWebRuntimeSessionTabsSnapshot(environmentId, args.worktreeId, {
-      expectedEnvironmentPairingRevision: intentOwner.pairingRevision
-    })
+    try {
+      await refreshWebRuntimeSessionTabsSnapshot(environmentId, args.worktreeId, {
+        expectedEnvironmentPairingRevision: intentOwner.pairingRevision
+      })
+    } catch (error) {
+      console.warn(
+        '[web-runtime-session] browser created but reconciliation failed:',
+        error instanceof Error ? error.message : String(error)
+      )
+    }
+    if (!staged) {
+      const stagedAfterRefresh = stageWebRuntimeBrowserTab({
+        environmentId,
+        worktreeId: args.worktreeId,
+        remotePageId: created.browserPageId,
+        url: args.url,
+        targetGroupId: args.clientTargetGroupId,
+        title: args.stagedTitle,
+        focusAddressBar: args.stagedFocusAddressBar,
+        restoreFocus: shouldSelectWorktree
+      })
+      if (stagedAfterRefresh && args.clientTargetGroupId) {
+        releaseWebSessionBrowserPlacementGroup({
+          environmentId,
+          worktreeId: args.worktreeId,
+          groupId: args.clientTargetGroupId
+        })
+      }
+    } else if (args.clientTargetGroupId) {
+      releaseWebSessionBrowserPlacementGroup({
+        environmentId,
+        worktreeId: args.worktreeId,
+        groupId: args.clientTargetGroupId
+      })
+    }
     return true
   } catch (error) {
+    if (args.clientTargetGroupId) {
+      releaseWebSessionBrowserPlacementGroup({
+        environmentId,
+        worktreeId: args.worktreeId,
+        groupId: args.clientTargetGroupId
+      })
+      if (args.clientTargetGroupCreated) {
+        useAppStore.getState().closeEmptyGroup(args.worktreeId, args.clientTargetGroupId)
+      }
+    }
     if (args.failureLogMode === 'operation-only') {
       console.warn('[web-runtime-session] failed to create browser tab')
     } else {
@@ -503,10 +570,10 @@ function stageWebRuntimeBrowserTab(args: {
   title?: string
   focusAddressBar?: boolean
   restoreFocus?: boolean
-}): void {
+}): boolean {
   const remotePageId = args.remotePageId.trim()
   if (!remotePageId) {
-    return
+    return false
   }
 
   const existing = findLocalBrowserPageForRemotePage(
@@ -519,12 +586,27 @@ function stageWebRuntimeBrowserTab(args: {
   }
 
   if (existing) {
+    if (args.targetGroupId) {
+      const state = useAppStore.getState()
+      const unifiedTab = (state.unifiedTabsByWorktree[args.worktreeId] ?? []).find(
+        (tab) => tab.contentType === 'browser' && tab.entityId === existing.workspaceId
+      )
+      if (!unifiedTab) {
+        return false
+      }
+      if (
+        unifiedTab.groupId !== args.targetGroupId &&
+        !state.moveUnifiedTabToGroup(unifiedTab.id, args.targetGroupId, { activate: true })
+      ) {
+        return false
+      }
+    }
     if (args.restoreFocus !== false) {
       useAppStore
         .getState()
         .focusBrowserTabInWorktree(args.worktreeId, existing.pageId, { surfacePane: true })
     }
-    return
+    return true
   }
 
   const url = args.url?.trim() || 'about:blank'
@@ -537,28 +619,36 @@ function stageWebRuntimeBrowserTab(args: {
   })
   const pageId = browserTab.activePageId ?? browserTab.pageIds?.[0] ?? null
   if (!pageId) {
-    return
+    return false
   }
   useAppStore.getState().setRemoteBrowserPageHandle(pageId, {
     environmentId: args.environmentId,
     remotePageId
   })
+  return true
 }
 
 function selectWebRuntimeSessionWorktree(worktreeId: string, environmentId: string): void {
-  useAppStore.getState().setActiveWorktree(worktreeId, toRuntimeExecutionHostId(environmentId))
+  const state = useAppStore.getState()
+  if (
+    state.activeWorktreeId === worktreeId &&
+    state.activeWorkspaceExecutionHostId === toRuntimeExecutionHostId(environmentId)
+  ) {
+    return
+  }
+  state.setActiveWorktree(worktreeId, toRuntimeExecutionHostId(environmentId))
 }
 
 function findLocalBrowserPageForRemotePage(
   state: AppState,
   environmentId: string,
   remotePageId: string
-): { pageId: string } | null {
-  for (const pages of Object.values(state.browserPagesByWorkspace)) {
+): { pageId: string; workspaceId: string } | null {
+  for (const [workspaceId, pages] of Object.entries(state.browserPagesByWorkspace)) {
     for (const page of pages) {
       const handle = state.remoteBrowserPageHandlesByPageId[page.id]
       if (handle?.environmentId === environmentId && handle.remotePageId === remotePageId) {
-        return { pageId: page.id }
+        return { pageId: page.id, workspaceId }
       }
     }
   }
@@ -873,6 +963,7 @@ async function callWebRuntimeSessionTabMethod(
   const intentOwner = captureWebSessionIntentOwner(environmentId)
   const callEnvironment = captureRuntimeEnvironmentCall(environmentId, intentOwner.pairingRevision)
   const closeIntentTabIds = new Set<string>()
+  let activationHostTabId: string | null = null
 
   const isClose = method === 'session.tabs.close'
   const isLifecycleClose = isClose && args.reason !== 'user'
@@ -898,6 +989,11 @@ async function callWebRuntimeSessionTabMethod(
   try {
     const { resolveHostSessionTabIdForWebSessionTab } = await import('./web-session-tabs-sync')
     const state = useAppStore.getState()
+    const isBrowserActivation =
+      !isClose &&
+      (state.unifiedTabsByWorktree?.[args.worktreeId] ?? []).some(
+        (tab) => tab.id === args.tabId && tab.contentType === 'browser'
+      )
     const hostTabId =
       resolveHostSessionTabIdForWebSessionTab(state, {
         environmentId,
@@ -908,6 +1004,9 @@ async function callWebRuntimeSessionTabMethod(
       // Why: suppress until the host confirms removal, else an in-flight pre-close snapshot flashes the tab back.
       closeIntentTabIds.add(hostTabId)
       recordWebSessionCloseIntent(intentOwner, args.worktreeId, hostTabId, Date.now())
+    } else if (isBrowserActivation) {
+      activationHostTabId = hostTabId
+      recordWebSessionFocusIntent(intentOwner, args.worktreeId, hostTabId)
     }
     const response = await callEnvironment({
       // Why: old hosts cannot route this additive method, so a generation
@@ -956,6 +1055,9 @@ async function callWebRuntimeSessionTabMethod(
     }
     return true
   } catch (error) {
+    if (activationHostTabId) {
+      clearWebSessionFocusIntentIfMatches(intentOwner, args.worktreeId, activationHostTabId)
+    }
     for (const hostTabId of closeIntentTabIds) {
       clearWebSessionCloseIntent(intentOwner, args.worktreeId, hostTabId)
     }
diff --git a/src/renderer/src/runtime/web-session-browser-placement.test.ts b/src/renderer/src/runtime/web-session-browser-placement.test.ts
new file mode 100644
index 00000000000..55d7cd5c74f
--- /dev/null
+++ b/src/renderer/src/runtime/web-session-browser-placement.test.ts
@@ -0,0 +1,102 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import {
+  clearWebSessionBrowserPlacementsForEnvironment,
+  clearWebSessionBrowserPlacementsForWorktree,
+  getWebSessionBrowserPlacementGroup,
+  isWebSessionBrowserPlacementGroupReserved,
+  recordWebSessionBrowserPlacement,
+  reserveWebSessionBrowserPlacementGroup,
+  resetWebSessionBrowserPlacementsForTests
+} from './web-session-browser-placement'
+
+const ENVIRONMENT_ID = 'environment-1'
+const WORKTREE_ID = 'worktree-1'
+
+afterEach(resetWebSessionBrowserPlacementsForTests)
+
+describe('web session browser placement', () => {
+  it('bounds pending page placements and group reservations', () => {
+    for (let index = 0; index < 129; index += 1) {
+      recordWebSessionBrowserPlacement({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        remotePageId: `page-${index}`,
+        groupId: `group-${index}`
+      })
+      reserveWebSessionBrowserPlacementGroup({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        groupId: `group-${index}`
+      })
+    }
+
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        remotePageId: 'page-0'
+      })
+    ).toBeUndefined()
+    expect(
+      isWebSessionBrowserPlacementGroupReserved({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        groupId: 'group-0'
+      })
+    ).toBe(false)
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        remotePageId: 'page-128'
+      })
+    ).toBe('group-128')
+  })
+
+  it('clears only the requested worktree or environment', () => {
+    for (const [environmentId, worktreeId, suffix] of [
+      [ENVIRONMENT_ID, WORKTREE_ID, 'target'],
+      [ENVIRONMENT_ID, 'worktree-2', 'sibling'],
+      ['environment-2', WORKTREE_ID, 'other-environment']
+    ] as const) {
+      recordWebSessionBrowserPlacement({
+        environmentId,
+        worktreeId,
+        remotePageId: `page-${suffix}`,
+        groupId: `group-${suffix}`
+      })
+      reserveWebSessionBrowserPlacementGroup({
+        environmentId,
+        worktreeId,
+        groupId: `group-${suffix}`
+      })
+    }
+
+    clearWebSessionBrowserPlacementsForWorktree(ENVIRONMENT_ID, WORKTREE_ID)
+
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: WORKTREE_ID,
+        remotePageId: 'page-target'
+      })
+    ).toBeUndefined()
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: ENVIRONMENT_ID,
+        worktreeId: 'worktree-2',
+        remotePageId: 'page-sibling'
+      })
+    ).toBe('group-sibling')
+
+    clearWebSessionBrowserPlacementsForEnvironment('environment-2')
+
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: 'environment-2',
+        worktreeId: WORKTREE_ID,
+        remotePageId: 'page-other-environment'
+      })
+    ).toBeUndefined()
+  })
+})
diff --git a/src/renderer/src/runtime/web-session-browser-placement.ts b/src/renderer/src/runtime/web-session-browser-placement.ts
new file mode 100644
index 00000000000..a5bd07231b9
--- /dev/null
+++ b/src/renderer/src/runtime/web-session-browser-placement.ts
@@ -0,0 +1,131 @@
+type BrowserPlacement = { groupId: string; seen: boolean }
+
+const placementsByPage = new Map<string, BrowserPlacement>()
+const reservedGroups = new Set<string>()
+const MAX_PENDING_PLACEMENTS = 128
+
+function evictOldest(entries: Map<string, unknown> | Set<string>): void {
+  const oldest = entries.keys().next().value
+  if (oldest !== undefined) {
+    entries.delete(oldest)
+  }
+}
+
+function pageKey(environmentId: string, worktreeId: string, remotePageId: string): string {
+  return `${environmentId}\0${worktreeId}\0${remotePageId}`
+}
+
+function groupKey(environmentId: string, worktreeId: string, groupId: string): string {
+  return `${environmentId}\0${worktreeId}\0${groupId}`
+}
+
+function worktreePrefix(environmentId: string, worktreeId: string): string {
+  return `${environmentId}\0${worktreeId}\0`
+}
+
+export function reserveWebSessionBrowserPlacementGroup(args: {
+  environmentId: string
+  worktreeId: string
+  groupId: string
+}): void {
+  while (reservedGroups.size >= MAX_PENDING_PLACEMENTS) {
+    evictOldest(reservedGroups)
+  }
+  reservedGroups.add(groupKey(args.environmentId, args.worktreeId, args.groupId))
+}
+
+export function releaseWebSessionBrowserPlacementGroup(args: {
+  environmentId: string
+  worktreeId: string
+  groupId: string
+}): void {
+  reservedGroups.delete(groupKey(args.environmentId, args.worktreeId, args.groupId))
+}
+
+export function isWebSessionBrowserPlacementGroupReserved(args: {
+  environmentId: string
+  worktreeId: string
+  groupId: string
+}): boolean {
+  return reservedGroups.has(groupKey(args.environmentId, args.worktreeId, args.groupId))
+}
+
+export function recordWebSessionBrowserPlacement(args: {
+  environmentId: string
+  worktreeId: string
+  remotePageId: string
+  groupId: string
+}): void {
+  while (placementsByPage.size >= MAX_PENDING_PLACEMENTS) {
+    evictOldest(placementsByPage)
+  }
+  placementsByPage.set(pageKey(args.environmentId, args.worktreeId, args.remotePageId), {
+    groupId: args.groupId,
+    seen: false
+  })
+}
+
+export function getWebSessionBrowserPlacementGroup(args: {
+  environmentId: string
+  worktreeId: string
+  remotePageId: string
+}): string | undefined {
+  const placement = placementsByPage.get(
+    pageKey(args.environmentId, args.worktreeId, args.remotePageId)
+  )
+  if (placement) {
+    placement.seen = true
+    releaseWebSessionBrowserPlacementGroup({ ...args, groupId: placement.groupId })
+  }
+  return placement?.groupId
+}
+
+export function pruneWebSessionBrowserPlacements(
+  environmentId: string,
+  worktreeId: string,
+  liveRemotePageIds: ReadonlySet<string>
+): void {
+  const prefix = worktreePrefix(environmentId, worktreeId)
+  for (const [key, placement] of placementsByPage) {
+    const remotePageId = key.startsWith(prefix) ? key.slice(prefix.length) : null
+    if (remotePageId && placement.seen && !liveRemotePageIds.has(remotePageId)) {
+      placementsByPage.delete(key)
+    }
+  }
+}
+
+export function clearWebSessionBrowserPlacementsForWorktree(
+  environmentId: string,
+  worktreeId: string
+): void {
+  const prefix = worktreePrefix(environmentId, worktreeId)
+  for (const key of placementsByPage.keys()) {
+    if (key.startsWith(prefix)) {
+      placementsByPage.delete(key)
+    }
+  }
+  for (const key of reservedGroups) {
+    if (key.startsWith(prefix)) {
+      reservedGroups.delete(key)
+    }
+  }
+}
+
+export function clearWebSessionBrowserPlacementsForEnvironment(environmentId: string): void {
+  const prefix = `${environmentId}\0`
+  for (const key of placementsByPage.keys()) {
+    if (key.startsWith(prefix)) {
+      placementsByPage.delete(key)
+    }
+  }
+  for (const key of reservedGroups) {
+    if (key.startsWith(prefix)) {
+      reservedGroups.delete(key)
+    }
+  }
+}
+
+export function resetWebSessionBrowserPlacementsForTests(): void {
+  placementsByPage.clear()
+  reservedGroups.clear()
+}
diff --git a/src/renderer/src/runtime/web-session-focus-intent.ts b/src/renderer/src/runtime/web-session-focus-intent.ts
index 8ed33b8d15e..e4d94e12f0f 100644
--- a/src/renderer/src/runtime/web-session-focus-intent.ts
+++ b/src/renderer/src/runtime/web-session-focus-intent.ts
@@ -50,6 +50,17 @@ export function clearWebSessionFocusIntent(owner: WebSessionIntentOwner, worktre
   pendingFocusByOwnerAndWorktree.delete(focusIntentPartitionKey(owner, worktreeId))
 }
 
+export function clearWebSessionFocusIntentIfMatches(
+  owner: WebSessionIntentOwner,
+  worktreeId: string,
+  hostTabId: string
+): void {
+  const key = focusIntentPartitionKey(owner, worktreeId)
+  if (pendingFocusByOwnerAndWorktree.get(key)?.hostTabId === hostTabId) {
+    pendingFocusByOwnerAndWorktree.delete(key)
+  }
+}
+
 export function clearWebSessionFocusIntentsForOwner(owner: WebSessionIntentOwner): void {
   const prefix = `${webSessionIntentOwnerKey(owner)}\0`
   for (const key of pendingFocusByOwnerAndWorktree.keys()) {
diff --git a/src/renderer/src/runtime/web-session-tabs-sync.test.ts b/src/renderer/src/runtime/web-session-tabs-sync.test.ts
index cad1147ed1e..5324eac70be 100644
--- a/src/renderer/src/runtime/web-session-tabs-sync.test.ts
+++ b/src/renderer/src/runtime/web-session-tabs-sync.test.ts
@@ -20,13 +20,24 @@ import {
   recordWebSessionReorderIntent,
   resetWebSessionReorderIntentForTests
 } from './web-session-reorder-intent'
-import type { BrowserPage, BrowserWorkspace, Tab, TerminalTab } from '../../../shared/types'
+import type {
+  BrowserPage,
+  BrowserWorkspace,
+  Tab,
+  TabGroupLayoutNode,
+  TerminalTab
+} from '../../../shared/types'
 import type { OpenFile } from '../store/slices/editor'
 import {
   confirmWebAgentSessionHandoffAfterCreate,
   recordWebAgentSessionHandoff,
   resetWebAgentSessionHandoffsForTests
 } from './web-agent-session-handoff'
+import {
+  getWebSessionBrowserPlacementGroup,
+  recordWebSessionBrowserPlacement,
+  reserveWebSessionBrowserPlacementGroup
+} from './web-session-browser-placement'
 import {
   _getWebSessionTabsTrackingCountsForTest,
   acceptReplayedWebSessionTabsSnapshot,
@@ -58,6 +69,16 @@ const SECOND_LEAF_ID = '22222222-2222-4222-8222-222222222222'
 const THIRD_LEAF_ID = '33333333-3333-4333-8333-333333333333'
 const HOST_SURFACE_ID = `host-tab-1::${LEAF_ID}`
 
+function layoutHasGroup(layout: TabGroupLayoutNode | undefined, groupId: string): boolean {
+  if (!layout) {
+    return false
+  }
+  if (layout.type === 'leaf') {
+    return layout.groupId === groupId
+  }
+  return layoutHasGroup(layout.first, groupId) || layoutHasGroup(layout.second, groupId)
+}
+
 function makeState(overrides: Partial<WebSessionTabsSyncState> = {}): WebSessionTabsSyncState {
   return {
     activeBrowserTabId: null,
@@ -3911,6 +3932,187 @@ describe('applyWebSessionTabsSnapshot', () => {
     expect(patch.layoutByWorktree).toBeUndefined()
   })
 
+  it('keeps one remote browser in its client-owned side-preview group', () => {
+    const editorGroupId = 'client-editor-group'
+    const previewGroupId = 'client-preview-group'
+    recordWebSessionBrowserPlacement({
+      environmentId: ENV,
+      worktreeId: WT,
+      remotePageId: 'host-browser-page',
+      groupId: previewGroupId
+    })
+
+    const patch = applyWebSessionTabsSnapshot(
+      makeState({
+        groupsByWorktree: {
+          [WT]: [
+            {
+              id: editorGroupId,
+              worktreeId: WT,
+              activeTabId: 'local-editor',
+              tabOrder: ['local-editor']
+            },
+            {
+              id: previewGroupId,
+              worktreeId: WT,
+              activeTabId: null,
+              tabOrder: []
+            }
+          ]
+        },
+        layoutByWorktree: {
+          [WT]: {
+            type: 'split',
+            direction: 'horizontal',
+            first: { type: 'leaf', groupId: editorGroupId },
+            second: { type: 'leaf', groupId: previewGroupId },
+            ratio: 0.5
+          }
+        },
+        unifiedTabsByWorktree: {
+          [WT]: [
+            {
+              id: 'local-editor',
+              worktreeId: WT,
+              groupId: editorGroupId,
+              contentType: 'editor',
+              entityId: 'local-file',
+              label: 'example.html',
+              sortOrder: 0,
+              createdAt: NOW,
+              isPreview: false,
+              isPinned: false,
+              customLabel: null,
+              color: null
+            }
+          ]
+        }
+      }),
+      makeSnapshot(
+        [
+          {
+            type: 'browser',
+            id: 'host-browser-tab',
+            title: 'example.html',
+            browserWorkspaceId: 'host-browser-workspace',
+            browserPageId: 'host-browser-page',
+            url: 'file:///srv/repo/example.html',
+            loading: false,
+            canGoBack: false,
+            canGoForward: false,
+            isActive: true
+          }
+        ],
+        { activeTabId: 'host-browser-tab', activeTabType: 'browser' }
+      ),
+      ENV,
+      NOW
+    ) as Partial<WebSessionTabsSyncState>
+
+    const browserTab = patch.unifiedTabsByWorktree?.[WT]?.find(
+      (tab) => tab.contentType === 'browser'
+    )
+    expect(browserTab).toMatchObject({ id: 'host-browser-tab', groupId: previewGroupId })
+    expect(
+      patch.groupsByWorktree?.[WT]?.find((group) => group.id === previewGroupId)
+    ).toMatchObject({ activeTabId: 'host-browser-tab', tabOrder: ['host-browser-tab'] })
+    expect(patch.groupsByWorktree?.[WT]?.find((group) => group.id === editorGroupId)).toMatchObject(
+      { activeTabId: 'local-editor', tabOrder: ['local-editor'] }
+    )
+    expect(patch.browserTabsByWorktree?.[WT]).toHaveLength(1)
+  })
+
+  it('keeps a reserved side-preview split across a pre-publication snapshot', () => {
+    const editorGroupId = 'client-editor-group'
+    const previewGroupId = 'client-preview-group'
+    const initialLayout: TabGroupLayoutNode = {
+      type: 'split',
+      direction: 'horizontal',
+      first: { type: 'leaf', groupId: editorGroupId },
+      second: { type: 'leaf', groupId: previewGroupId },
+      ratio: 0.5
+    }
+    reserveWebSessionBrowserPlacementGroup({
+      environmentId: ENV,
+      worktreeId: WT,
+      groupId: previewGroupId
+    })
+
+    const patch = applyWebSessionTabsSnapshot(
+      makeState({
+        groupsByWorktree: {
+          [WT]: [
+            {
+              id: editorGroupId,
+              worktreeId: WT,
+              activeTabId: 'local-editor',
+              tabOrder: ['local-editor']
+            },
+            {
+              id: previewGroupId,
+              worktreeId: WT,
+              activeTabId: null,
+              tabOrder: []
+            }
+          ]
+        },
+        layoutByWorktree: { [WT]: initialLayout },
+        unifiedTabsByWorktree: {
+          [WT]: [
+            {
+              id: 'local-editor',
+              worktreeId: WT,
+              groupId: editorGroupId,
+              contentType: 'editor',
+              entityId: 'local-file',
+              label: 'example.html',
+              sortOrder: 0,
+              createdAt: NOW,
+              isPreview: false,
+              isPinned: false,
+              customLabel: null,
+              color: null
+            }
+          ]
+        }
+      }),
+      makeSnapshot([], {
+        activeTabType: null,
+        tabGroups: [{ id: editorGroupId, activeTabId: null, tabOrder: [], recentTabIds: [] }],
+        tabGroupLayout: { type: 'leaf', groupId: editorGroupId }
+      }),
+      ENV,
+      NOW
+    ) as Partial<WebSessionTabsSyncState>
+
+    expect(patch.groupsByWorktree?.[WT]?.map((group) => group.id)).toContain(previewGroupId)
+    expect(layoutHasGroup(patch.layoutByWorktree?.[WT] ?? initialLayout, previewGroupId)).toBe(true)
+  })
+
+  it('forgets client browser placement after the host removes the page', () => {
+    recordWebSessionBrowserPlacement({
+      environmentId: ENV,
+      worktreeId: WT,
+      remotePageId: 'host-browser-page',
+      groupId: 'client-preview-group'
+    })
+    getWebSessionBrowserPlacementGroup({
+      environmentId: ENV,
+      worktreeId: WT,
+      remotePageId: 'host-browser-page'
+    })
+
+    applyWebSessionTabsSnapshot(makeState(), makeSnapshot([]), ENV, NOW)
+
+    expect(
+      getWebSessionBrowserPlacementGroup({
+        environmentId: ENV,
+        worktreeId: WT,
+        remotePageId: 'host-browser-page'
+      })
+    ).toBeUndefined()
+  })
+
   it('creates a rendered web layout group when stale group records do not include it', () => {
     const visibleGroupId = 'visible-web-group'
     const hostOnlyGroupId = 'host-group-1'
diff --git a/src/renderer/src/runtime/web-session-tabs-sync.ts b/src/renderer/src/runtime/web-session-tabs-sync.ts
index 107c085db4e..195623d2e1d 100644
--- a/src/renderer/src/runtime/web-session-tabs-sync.ts
+++ b/src/renderer/src/runtime/web-session-tabs-sync.ts
@@ -90,6 +90,14 @@ import {
   installWindowVisibilitySubscriptionParking,
   type WindowVisibilitySubscriptionSpec
 } from './window-visibility-subscription-parking'
+import {
+  clearWebSessionBrowserPlacementsForEnvironment,
+  clearWebSessionBrowserPlacementsForWorktree,
+  getWebSessionBrowserPlacementGroup,
+  isWebSessionBrowserPlacementGroupReserved,
+  pruneWebSessionBrowserPlacements,
+  resetWebSessionBrowserPlacementsForTests
+} from './web-session-browser-placement'
 
 const WEB_SESSION_GROUP_PREFIX = 'web-session-tabs:'
 export const WEB_SESSION_TABS_VISIBILITY_RESUME_STAGGER_MS = 100
@@ -170,6 +178,7 @@ type MirroredBrowserTab = {
   remotePageId: string
   unifiedTab: Tab
   hostTabId: string
+  clientGroupId?: string
 }
 
 type MirroredEditorTab = {
@@ -633,6 +642,7 @@ export function resetWebSessionTabsSnapshotFreshnessForTests(): void {
   lastHostTerminalTabCountByWorktree.clear()
   hostSessionTabIdByLocalKey.clear()
   hostSessionTabMappingKeysByEnvironmentAndWorktree.clear()
+  resetWebSessionBrowserPlacementsForTests()
 }
 
 export function _getWebSessionTabsTrackingCountsForTest(): {
@@ -675,6 +685,7 @@ function clearWebSessionTabsTrackingForWorktree(environmentId: string, worktreeI
   clearWebSessionCloseIntentsForWorktree({ environmentId }, worktreeId)
   clearWebAgentSessionHandoffsForWorktree(environmentId, worktreeId)
   clearHostSessionTabIdMappings(environmentId, worktreeId)
+  clearWebSessionBrowserPlacementsForWorktree(environmentId, worktreeId)
 }
 
 export function clearWebSessionTabsTrackingForEnvironment(environmentId: string): void {
@@ -728,6 +739,7 @@ export function clearWebSessionTabsTrackingForEnvironment(environmentId: string)
     hostSessionTabMappingKeysByEnvironmentAndWorktree.delete(trimmedEnvironmentId)
   }
   clearWebAgentSessionHandoffsForEnvironment(trimmedEnvironmentId)
+  clearWebSessionBrowserPlacementsForEnvironment(trimmedEnvironmentId)
   clearAllWebRuntimeWakeTerminalRespawn()
 }
 
@@ -1494,6 +1506,10 @@ function buildMirroredBrowserTabs(
   sortOffset: number,
   now: number
 ): MirroredBrowserTab[] {
+  const renderedGroupIds = collectLayoutGroupIds(state.layoutByWorktree[snapshot.worktree])
+  const clientGroupIds = new Set(
+    (state.groupsByWorktree[snapshot.worktree] ?? []).map((group) => group.id)
+  )
   return snapshot.tabs.filter(isReadyBrowserTab).map((tab, index) => {
     const existing = findBrowserWorkspaceForRemotePage(
       state,
@@ -1504,7 +1520,18 @@ function buildMirroredBrowserTabs(
     const workspaceId = existing?.workspace.id ?? tab.browserWorkspaceId
     const pageId = existing?.page.id ?? tab.browserPageId
     const createdAt = existing?.page.createdAt ?? now + sortOffset + index
-    const groupId = hostGroupIdByTabId.get(tab.id) ?? fallbackGroupId
+    const recordedClientGroupId = getWebSessionBrowserPlacementGroup({
+      environmentId,
+      worktreeId: snapshot.worktree,
+      remotePageId: tab.browserPageId
+    })
+    const clientGroupId =
+      recordedClientGroupId &&
+      clientGroupIds.has(recordedClientGroupId) &&
+      (renderedGroupIds.size === 0 || renderedGroupIds.has(recordedClientGroupId))
+        ? recordedClientGroupId
+        : undefined
+    const groupId = clientGroupId ?? hostGroupIdByTabId.get(tab.id) ?? fallbackGroupId
     const title = tab.title.trim() || 'Browser'
     const nextPage: BrowserPage = {
       id: pageId,
@@ -1546,7 +1573,8 @@ function buildMirroredBrowserTabs(
       certificateFailure: tab.certificateFailure ?? null,
       remotePageId: tab.browserPageId,
       unifiedTab: buildBrowserUnifiedTab(workspace, tab, existing?.unifiedTab ?? null, groupId),
-      hostTabId: tab.id
+      hostTabId: tab.id,
+      ...(clientGroupId ? { clientGroupId } : {})
     }
   })
 }
@@ -1745,7 +1773,8 @@ function buildMirroredHostGroups({
   now,
   validUnifiedTabIds,
   environmentId,
-  worktreeId
+  worktreeId,
+  clientGroupIdByLocalTabId
 }: {
   currentGroups: readonly TabGroup[]
   hostGroups: readonly RuntimeMobileSessionTabGroup[]
@@ -1756,15 +1785,34 @@ function buildMirroredHostGroups({
   validUnifiedTabIds: ReadonlySet<string>
   environmentId: string
   worktreeId: string
+  clientGroupIdByLocalTabId: ReadonlyMap<string, string>
 }): TabGroup[] | null {
   const strippedGroups = currentGroups.map((group) => {
-    const tabOrder = group.tabOrder.filter(
-      (tabId) => validUnifiedTabIds.has(tabId) && !mirroredUnifiedIds.has(tabId)
+    const retainedTabOrder = group.tabOrder.filter(
+      (tabId) =>
+        validUnifiedTabIds.has(tabId) &&
+        (!mirroredUnifiedIds.has(tabId) || clientGroupIdByLocalTabId.get(tabId) === group.id)
     )
+    const placedTabIds = [...clientGroupIdByLocalTabId]
+      .filter(
+        ([tabId, groupId]) =>
+          groupId === group.id && validUnifiedTabIds.has(tabId) && !retainedTabOrder.includes(tabId)
+      )
+      .map(([tabId]) => tabId)
+    const tabOrder = [...retainedTabOrder, ...placedTabIds]
+    const activeTabId =
+      nextActiveUnifiedTabId && tabOrder.includes(nextActiveUnifiedTabId)
+        ? nextActiveUnifiedTabId
+        : group.activeTabId && tabOrder.includes(group.activeTabId)
+          ? group.activeTabId
+          : (tabOrder[0] ?? null)
     return {
       ...group,
       tabOrder,
-      recentTabIds: sanitizeRecentTabIds(group.recentTabIds, tabOrder)
+      activeTabId,
+      recentTabIds: activeTabId
+        ? pushRecentTabId(sanitizeRecentTabIds(group.recentTabIds, tabOrder), activeTabId)
+        : []
     }
   })
   const groupsById = new Map(strippedGroups.map((group) => [group.id, group]))
@@ -1775,7 +1823,12 @@ function buildMirroredHostGroups({
     const existing = groupsById.get(hostGroup.id)
     const localHostOrder = hostGroup.tabOrder
       .map((tabId) => hostToLocalTabId.get(tabId))
-      .filter((tabId): tabId is string => tabId !== undefined && validUnifiedTabIds.has(tabId))
+      .filter(
+        (tabId): tabId is string =>
+          tabId !== undefined &&
+          validUnifiedTabIds.has(tabId) &&
+          !clientGroupIdByLocalTabId.has(tabId)
+      )
     const hostTabOrder = [
       ...(existing?.tabOrder.filter((tabId) => !localHostOrder.includes(tabId)) ?? []),
       ...localHostOrder
@@ -1817,7 +1870,11 @@ function buildMirroredHostGroups({
   }
 
   for (const group of strippedGroups) {
-    if (!seen.has(group.id) && group.tabOrder.length > 0) {
+    if (
+      !seen.has(group.id) &&
+      (group.tabOrder.length > 0 ||
+        isWebSessionBrowserPlacementGroupReserved({ environmentId, worktreeId, groupId: group.id }))
+    ) {
       orderedGroups.push(group)
     }
   }
@@ -2408,6 +2465,7 @@ function applyWebSessionTabsSnapshotWithContext(
   const hostGroupIdByTabId = buildHostGroupIdByTabId(snapshot.tabGroups)
   const readyBrowserTabs = snapshot.tabs.filter(isReadyBrowserTab)
   const nextRemoteBrowserPageIds = new Set(readyBrowserTabs.map((tab) => tab.browserPageId))
+  pruneWebSessionBrowserPlacements(environmentId, worktreeId, nextRemoteBrowserPageIds)
   const mirroredBrowserTabs = buildMirroredBrowserTabs(
     snapshot,
     environmentId,
@@ -2692,6 +2750,11 @@ function applyWebSessionTabsSnapshotWithContext(
   })
 
   const currentGroups = state.groupsByWorktree[worktreeId] ?? []
+  const clientGroupIdByLocalTabId = new Map(
+    mirroredBrowserTabs.flatMap((entry) =>
+      entry.clientGroupId ? [[entry.unifiedTab.id, entry.clientGroupId]] : []
+    )
+  )
   const nextGroups = (() => {
     if (!nextUnifiedTabs || nextUnifiedTabs.length === 0) {
       return null
@@ -2706,21 +2769,40 @@ function applyWebSessionTabsSnapshotWithContext(
         now,
         validUnifiedTabIds,
         environmentId,
-        worktreeId
+        worktreeId,
+        clientGroupIdByLocalTabId
       })
     }
-    const strippedGroups = currentGroups.map((group) => ({
-      ...group,
-      tabOrder: group.tabOrder.filter(
-        (tabId) => validUnifiedTabIds.has(tabId) && !mirroredUnifiedIds.has(tabId)
-      ),
-      recentTabIds: sanitizeRecentTabIds(
-        group.recentTabIds,
-        group.tabOrder.filter(
-          (tabId) => validUnifiedTabIds.has(tabId) && !mirroredUnifiedIds.has(tabId)
-        )
+    const strippedGroups = currentGroups.map((group) => {
+      const retainedTabOrder = group.tabOrder.filter(
+        (tabId) =>
+          validUnifiedTabIds.has(tabId) &&
+          (!mirroredUnifiedIds.has(tabId) || clientGroupIdByLocalTabId.get(tabId) === group.id)
       )
-    }))
+      const placedTabIds = [...clientGroupIdByLocalTabId]
+        .filter(
+          ([tabId, groupId]) =>
+            groupId === group.id &&
+            validUnifiedTabIds.has(tabId) &&
+            !retainedTabOrder.includes(tabId)
+        )
+        .map(([tabId]) => tabId)
+      const tabOrder = [...retainedTabOrder, ...placedTabIds]
+      const activeTabId =
+        nextActiveUnifiedTabId && tabOrder.includes(nextActiveUnifiedTabId)
+          ? nextActiveUnifiedTabId
+          : group.activeTabId && tabOrder.includes(group.activeTabId)
+            ? group.activeTabId
+            : (tabOrder[0] ?? null)
+      return {
+        ...group,
+        tabOrder,
+        activeTabId,
+        recentTabIds: activeTabId
+          ? pushRecentTabId(sanitizeRecentTabIds(group.recentTabIds, tabOrder), activeTabId)
+          : []
+      }
+    })
     const target = strippedGroups.find((group) => group.id === targetGroupId) ?? {
       id: targetGroupId,
       worktreeId,
@@ -2730,7 +2812,9 @@ function applyWebSessionTabsSnapshotWithContext(
     }
     const targetOrder = [
       ...target.tabOrder.filter((tabId) => validUnifiedTabIds.has(tabId)),
-      ...mirroredUnifiedTabs.map((tab) => tab.id)
+      ...mirroredUnifiedTabs
+        .filter((tab) => !clientGroupIdByLocalTabId.has(tab.id))
+        .map((tab) => tab.id)
     ]
     const targetActiveTabId =
       nextActiveUnifiedTabId && targetOrder.includes(nextActiveUnifiedTabId)
@@ -2750,7 +2834,16 @@ function applyWebSessionTabsSnapshotWithContext(
     const merged = strippedGroups.some((group) => group.id === targetGroupId)
       ? strippedGroups.map((group) => (group.id === targetGroupId ? updatedTarget : group))
       : [...strippedGroups, updatedTarget]
-    return merged.filter((group) => group.id === targetGroupId || group.tabOrder.length > 0)
+    return merged.filter(
+      (group) =>
+        group.id === targetGroupId ||
+        group.tabOrder.length > 0 ||
+        isWebSessionBrowserPlacementGroupReserved({
+          environmentId,
+          worktreeId,
+          groupId: group.id
+        })
+    )
   })()
 
   const nextTabBarOrder = (() => {
diff --git a/tests/e2e/paired-remote-html-browser-focus.spec.ts b/tests/e2e/paired-remote-html-browser-focus.spec.ts
new file mode 100644
index 00000000000..f8e9302b415
--- /dev/null
+++ b/tests/e2e/paired-remote-html-browser-focus.spec.ts
@@ -0,0 +1,436 @@
+import { writeFileSync } from 'node:fs'
+import path from 'node:path'
+import { expect, test } from './helpers/orca-app'
+import { openFileExplorer } from './helpers/file-explorer'
+import {
+  createRuntimeDesktopPairingOffer,
+  launchPairedElectronClient,
+  type PairedElectronClient
+} from './helpers/paired-electron-client'
+import { ensureTerminalVisible, waitForActiveWorktree, waitForSessionReady } from './helpers/store'
+
+const FIXTURE_NAME = 'paired-html-focus.html'
+
+test('keeps a selected remote HTML browser tab focused after host adoption', async ({
+  orcaPage,
+  testRepoPath
+}, testInfo) => {
+  test.setTimeout(240_000)
+  writeFileSync(
+    path.join(testRepoPath, FIXTURE_NAME),
+    '<!doctype html><html><body><h1>paired html focus</h1></body></html>\n'
+  )
+  await waitForSessionReady(orcaPage)
+  await waitForActiveWorktree(orcaPage)
+  await ensureTerminalVisible(orcaPage)
+
+  const offer = await createRuntimeDesktopPairingOffer(orcaPage)
+  let client: PairedElectronClient | null = null
+  try {
+    client = await launchPairedElectronClient(offer, testInfo, 'Remote HTML focus')
+    const page = client.page
+    const worktreeId = await expect
+      .poll(
+        () =>
+          page.evaluate((repoPath) => {
+            const state = window.__store?.getState()
+            return state
+              ? (state.allWorktrees().find((worktree) => worktree.path === repoPath)?.id ?? null)
+              : null
+          }, testRepoPath),
+        { timeout: 60_000, message: 'paired client never received the host worktree' }
+      )
+      .not.toBeNull()
+      .then(() =>
+        page.evaluate((repoPath) => {
+          const state = window.__store?.getState()
+          return state?.allWorktrees().find((worktree) => worktree.path === repoPath)?.id ?? null
+        }, testRepoPath)
+      )
+    if (!worktreeId) {
+      throw new Error('paired client worktree disappeared after discovery')
+    }
+    await page.evaluate(
+      ({ environmentId, worktreeId }) => {
+        window.__store?.getState().setActiveWorktree(worktreeId, `runtime:${environmentId}`)
+      },
+      { environmentId: client.environmentId, worktreeId }
+    )
+    await openFileExplorer(page)
+    const fixtureRow = page.locator('[data-file-explorer-row]').filter({ hasText: FIXTURE_NAME })
+    await expect(fixtureRow).toBeVisible({ timeout: 30_000 })
+    await fixtureRow.click()
+    const openPreviewToSide = page.getByRole('button', { name: 'Open Preview to the Side' })
+    await expect(openPreviewToSide).toBeVisible({ timeout: 30_000 })
+    const sourceEditor = await page.evaluate((targetWorktreeId) => {
+      const state = window.__store?.getState()
+      const groupId = state?.activeGroupIdByWorktree[targetWorktreeId]
+      const group = (state?.groupsByWorktree[targetWorktreeId] ?? []).find(
+        (candidate) => candidate.id === groupId
+      )
+      const tab = (state?.unifiedTabsByWorktree[targetWorktreeId] ?? []).find(
+        (candidate) => candidate.id === group?.activeTabId && candidate.contentType === 'editor'
+      )
+      return groupId && tab ? { groupId, tabId: tab.id } : null
+    }, worktreeId)
+    if (!sourceEditor) {
+      throw new Error('paired client editor had no source identity before side preview')
+    }
+    const sourceGroupId = sourceEditor.groupId
+    const browserBaseline = await page.evaluate(
+      async ({ environmentId, worktreeId }) => {
+        const state = window.__store?.getState()
+        const response = await window.api.runtimeEnvironments.call({
+          selector: environmentId,
+          method: 'session.tabs.list',
+          params: { worktree: `id:${worktreeId}` },
+          timeoutMs: 15_000
+        })
+        return {
+          clientUnified: (state?.unifiedTabsByWorktree[worktreeId] ?? []).filter(
+            (tab) => tab.contentType === 'browser'
+          ).length,
+          clientWorkspaces: (state?.browserTabsByWorktree[worktreeId] ?? []).length,
+          host: response.ok
+            ? response.result.tabs.filter((tab) => tab.type === 'browser').length
+            : -1
+        }
+      },
+      { environmentId: client.environmentId, worktreeId }
+    )
+    await openPreviewToSide.click()
+
+    await expect
+      .poll(
+        () =>
+          page.evaluate(
+            async ({ environmentId, fixtureName, worktreeId }) => {
+              const state = window.__store?.getState()
+              if (!state) {
+                return null
+              }
+              const browser = (state.browserTabsByWorktree[worktreeId] ?? []).find((tab) =>
+                tab.url.endsWith(`/${fixtureName}`)
+              )
+              const browserPage = browser
+                ? (state.browserPagesByWorkspace[browser.id] ?? [])[0]
+                : null
+              const handle = browserPage
+                ? state.remoteBrowserPageHandlesByPageId[browserPage.id]
+                : null
+              const response = await window.api.runtimeEnvironments.call({
+                selector: environmentId,
+                method: 'session.tabs.list',
+                params: { worktree: `id:${worktreeId}` },
+                timeoutMs: 15_000
+              })
+              const hostHasHtml =
+                response.ok &&
+                response.result.tabs.some(
+                  (tab) => tab.type === 'browser' && tab.url.endsWith(`/${fixtureName}`)
+                )
+              return {
+                browserRuntimeEnvironmentId: browserPage?.browserRuntimeEnvironmentId ?? null,
+                handleEnvironmentId: handle?.environmentId ?? null,
+                handleRemotePageId: handle?.remotePageId ?? null,
+                hostHasHtml
+              }
+            },
+            { environmentId: client!.environmentId, fixtureName: FIXTURE_NAME, worktreeId }
+          ),
+        { timeout: 60_000, message: 'remote HTML browser ownership never converged' }
+      )
+      .toMatchObject({
+        browserRuntimeEnvironmentId: client.environmentId,
+        handleEnvironmentId: client.environmentId,
+        hostHasHtml: true
+      })
+    const htmlTabInventory = await page.evaluate(
+      async ({ environmentId, fixtureName, worktreeId }) => {
+        const state = window.__store?.getState()
+        const response = await window.api.runtimeEnvironments.call({
+          selector: environmentId,
+          method: 'session.tabs.list',
+          params: { worktree: `id:${worktreeId}` },
+          timeoutMs: 15_000
+        })
+        const clientWorkspaceIds = (state?.browserTabsByWorktree[worktreeId] ?? [])
+          .filter((tab) => tab.url.endsWith(`/${fixtureName}`))
+          .map((tab) => tab.id)
+        return {
+          clientWorkspaceIds,
+          clientUnifiedTabs: (state?.unifiedTabsByWorktree[worktreeId] ?? [])
+            .filter(
+              (tab) => tab.contentType === 'browser' && clientWorkspaceIds.includes(tab.entityId)
+            )
+            .map((tab) => ({ groupId: tab.groupId, id: tab.id })),
+          hostTabIds: response.ok
+            ? response.result.tabs
+                .filter((tab) => tab.type === 'browser' && tab.url.endsWith(`/${fixtureName}`))
+                .map((tab) => tab.id)
+            : [],
+          hostTabGroups: response.ok ? (response.result.tabGroups ?? []) : [],
+          totalClientUnified: (state?.unifiedTabsByWorktree[worktreeId] ?? []).filter(
+            (tab) => tab.contentType === 'browser'
+          ).length,
+          totalClientWorkspaces: (state?.browserTabsByWorktree[worktreeId] ?? []).length,
+          totalHost: response.ok
+            ? response.result.tabs.filter((tab) => tab.type === 'browser').length
+            : -1
+        }
+      },
+      { environmentId: client.environmentId, fixtureName: FIXTURE_NAME, worktreeId }
+    )
+    expect(htmlTabInventory.clientWorkspaceIds).toHaveLength(1)
+    expect(htmlTabInventory.clientUnifiedTabs).toHaveLength(1)
+    expect(htmlTabInventory.hostTabIds).toHaveLength(1)
+    expect(htmlTabInventory.totalClientUnified).toBe(browserBaseline.clientUnified + 1)
+    expect(htmlTabInventory.totalClientWorkspaces).toBe(browserBaseline.clientWorkspaces + 1)
+    expect(htmlTabInventory.totalHost).toBe(browserBaseline.host + 1)
+    expect(htmlTabInventory.clientUnifiedTabs[0]?.groupId).not.toBe(sourceGroupId)
+    expect(
+      htmlTabInventory.hostTabGroups.some(
+        (group) => group.id === htmlTabInventory.clientUnifiedTabs[0]?.groupId
+      )
+    ).toBe(false)
+    const hostBrowserGroupId = htmlTabInventory.hostTabGroups.find((group) =>
+      group.tabOrder.includes(htmlTabInventory.hostTabIds[0]!)
+    )?.id
+    expect(hostBrowserGroupId).toBeTruthy()
+    await expect(page.locator(`[data-tab-group-body-id="${sourceGroupId}"]`)).toBeVisible()
+    await expect(
+      page.locator(`[data-tab-group-body-id="${htmlTabInventory.clientUnifiedTabs[0]!.groupId}"]`)
+    ).toBeVisible()
+    await expect(page.getByTestId('remote-browser-frame')).toBeVisible({ timeout: 60_000 })
+
+    const tabIds = await page.evaluate(
+      ({ fixtureName, worktreeId: targetWorktreeId }) => {
+        const state = window.__store?.getState()
+        if (!state) {
+          return null
+        }
+        const terminalId = state.tabsByWorktree[targetWorktreeId]?.[0]?.id ?? null
+        const browserId = (state.browserTabsByWorktree[targetWorktreeId] ?? []).find((tab) =>
+          tab.url.endsWith(`/${fixtureName}`)
+        )?.id
+        return terminalId && browserId ? { browserId, terminalId } : null
+      },
+      { fixtureName: FIXTURE_NAME, worktreeId }
+    )
+    if (!tabIds) {
+      throw new Error('paired client did not retain both terminal and HTML browser tabs')
+    }
+    await page.locator(`[data-tab-id="${tabIds.terminalId}"]`).click()
+    await expect
+      .poll(
+        () =>
+          page.evaluate((targetWorktreeId) => {
+            const state = window.__store?.getState()
+            return state?.activeTabTypeByWorktree[targetWorktreeId] ?? null
+          }, worktreeId),
+        { message: 'terminal tab never became active before the browser click' }
+      )
+      .toBe('terminal')
+    await expect
+      .poll(
+        () =>
+          page.evaluate(
+            async ({ environmentId, worktreeId }) => {
+              const response = await window.api.runtimeEnvironments.call({
+                selector: environmentId,
+                method: 'session.tabs.list',
+                params: { worktree: `id:${worktreeId}` },
+                timeoutMs: 15_000
+              })
+              if (!response.ok) {
+                return false
+              }
+              return (
+                response.result.tabs.find((tab) => tab.id === response.result.activeTabId)?.type ===
+                'terminal'
+              )
+            },
+            { environmentId: client.environmentId, worktreeId }
+          ),
+        { timeout: 30_000, message: 'host never accepted terminal activation' }
+      )
+      .toBe(true)
+    const hostBrowserTab = await page.evaluate(
+      async ({ environmentId, fixtureName, worktreeId }) => {
+        const response = await window.api.runtimeEnvironments.call({
+          selector: environmentId,
+          method: 'session.tabs.list',
+          params: { worktree: `id:${worktreeId}` },
+          timeoutMs: 15_000
+        })
+        const tab = response.ok
+          ? response.result.tabs.find(
+              (candidate) =>
+                candidate.type === 'browser' && candidate.url.endsWith(`/${fixtureName}`)
+            )
+          : null
+        return tab?.type === 'browser' ? { browserPageId: tab.browserPageId, id: tab.id } : null
+      },
+      { environmentId: client.environmentId, fixtureName: FIXTURE_NAME, worktreeId }
+    )
+    if (!hostBrowserTab?.browserPageId) {
+      throw new Error('host HTML browser tab disappeared before activation')
+    }
+    const clientRemotePageId = await page.evaluate(
+      ({ fixtureName, worktreeId }) => {
+        const state = window.__store?.getState()
+        const workspace = (state?.browserTabsByWorktree[worktreeId] ?? []).find((tab) =>
+          tab.url.endsWith(`/${fixtureName}`)
+        )
+        const browserPage = workspace
+          ? (state?.browserPagesByWorkspace[workspace.id] ?? [])[0]
+          : null
+        return browserPage
+          ? (state?.remoteBrowserPageHandlesByPageId[browserPage.id]?.remotePageId ?? null)
+          : null
+      },
+      { fixtureName: FIXTURE_NAME, worktreeId }
+    )
+    expect(clientRemotePageId).toBe(hostBrowserTab.browserPageId)
+    const content = await page.evaluate(
+      async ({ browserPageId, environmentId, worktreeId }) =>
+        window.api.runtimeEnvironments.call({
+          selector: environmentId,
+          method: 'browser.eval',
+          params: {
+            worktree: `id:${worktreeId}`,
+            page: browserPageId,
+            expression: 'document.querySelector("h1")?.textContent'
+          },
+          timeoutMs: 15_000
+        }),
+      {
+        browserPageId: hostBrowserTab.browserPageId,
+        environmentId: client.environmentId,
+        worktreeId
+      }
+    )
+    expect(content).toMatchObject({ ok: true, result: { result: 'paired html focus' } })
+    await expect
+      .poll(
+        () =>
+          page.evaluate(
+            ({ browserTabId, environmentId }) => {
+              const state = window.__store?.getState()
+              return (state?.browserPagesByWorkspace[browserTabId] ?? []).some((browserPage) => {
+                const handle = state?.remoteBrowserPageHandlesByPageId[browserPage.id]
+                return (
+                  handle?.environmentId === environmentId ||
+                  browserPage.browserRuntimeEnvironmentId === environmentId
+                )
+              })
+            },
+            { browserTabId: tabIds.browserId, environmentId: client.environmentId }
+          ),
+        { timeout: 30_000, message: 'client lost remote browser ownership before activation' }
+      )
+      .toBe(true)
+    await page.locator(`[data-tab-id="${tabIds.browserId}"]`).click()
+
+    await expect
+      .poll(
+        () =>
+          page.evaluate(
+            async ({ environmentId, fixtureName, worktreeId }) => {
+              const state = window.__store?.getState()
+              if (!state) {
+                return null
+              }
+              const response = await window.api.runtimeEnvironments.call({
+                selector: environmentId,
+                method: 'session.tabs.list',
+                params: { worktree: `id:${worktreeId}` },
+                timeoutMs: 15_000
+              })
+              const activeGroup = (state.groupsByWorktree[worktreeId] ?? []).find(
+                (group) => group.id === state.activeGroupIdByWorktree[worktreeId]
+              )
+              const activeUnified = (state.unifiedTabsByWorktree[worktreeId] ?? []).find(
+                (tab) => tab.id === activeGroup?.activeTabId
+              )
+              const hostActive = response.ok
+                ? response.result.tabs.find((tab) => tab.id === response.result.activeTabId)
+                : null
+              return {
+                activeGroupType: activeUnified?.contentType ?? null,
+                activeTabType: state.activeTabTypeByWorktree[worktreeId] ?? null,
+                hostActiveHtml:
+                  hostActive?.type === 'browser' && hostActive.url.endsWith(`/${fixtureName}`)
+              }
+            },
+            { environmentId: client!.environmentId, fixtureName: FIXTURE_NAME, worktreeId }
+          ),
+        { timeout: 30_000, message: 'browser click did not remain authoritative' }
+      )
+      .toEqual({ activeGroupType: 'browser', activeTabType: 'browser', hostActiveHtml: true })
+    await expect(page.getByTestId('remote-browser-frame')).toBeVisible()
+
+    const browserTab = page.locator(`[data-tab-id="${tabIds.browserId}"]`)
+    await browserTab.click({ button: 'right' })
+    await page.getByRole('menuitem', { name: 'Close', exact: true }).click()
+    await expect
+      .poll(
+        () =>
+          page.evaluate(
+            async ({
+              environmentId,
+              hostTabId,
+              sourceGroupId,
+              unifiedTabId,
+              workspaceId,
+              worktreeId
+            }) => {
+              const state = window.__store?.getState()
+              const response = await window.api.runtimeEnvironments.call({
+                selector: environmentId,
+                method: 'session.tabs.list',
+                params: { worktree: `id:${worktreeId}` },
+                timeoutMs: 15_000
+              })
+              return {
+                clientUnifiedPresent: (state?.unifiedTabsByWorktree[worktreeId] ?? []).some(
+                  (tab) => tab.id === unifiedTabId
+                ),
+                clientWorkspacePresent: (state?.browserTabsByWorktree[worktreeId] ?? []).some(
+                  (tab) => tab.id === workspaceId
+                ),
+                hostTabPresent: response.ok
+                  ? response.result.tabs.some((tab) => tab.id === hostTabId)
+                  : true,
+                sourceGroupPresent: (state?.groupsByWorktree[worktreeId] ?? []).some(
+                  (group) => group.id === sourceGroupId
+                )
+              }
+            },
+            {
+              environmentId: client!.environmentId,
+              hostTabId: hostBrowserTab.id,
+              sourceGroupId,
+              unifiedTabId: htmlTabInventory.clientUnifiedTabs[0]!.id,
+              workspaceId: htmlTabInventory.clientWorkspaceIds[0]!,
+              worktreeId
+            }
+          ),
+        { timeout: 30_000, message: 'remote HTML browser close did not converge cleanly' }
+      )
+      .toEqual({
+        clientUnifiedPresent: false,
+        clientWorkspacePresent: false,
+        hostTabPresent: false,
+        sourceGroupPresent: true
+      })
+    await expect(browserTab).toHaveCount(0)
+    await expect(page.locator(`[data-tab-id="${tabIds.terminalId}"]`)).toBeVisible()
+    await expect(page.locator(`[data-tab-id="${sourceEditor.tabId}"]`)).toBeVisible()
+    await expect(
+      page.locator(`[data-tab-group-body-id="${sourceGroupId}"] .monaco-editor`)
+    ).toBeVisible()
+  } finally {
+    await client?.dispose()
+  }
+})