diff --git a/src/renderer/src/components/activity/activity-answered-ask-timeline.test.tsx b/src/renderer/src/components/activity/activity-answered-ask-timeline.test.tsx
index 49e53f64f7e..0f6a44629fc 100644
--- a/src/renderer/src/components/activity/activity-answered-ask-timeline.test.tsx
+++ b/src/renderer/src/components/activity/activity-answered-ask-timeline.test.tsx
@@ -40,8 +40,6 @@ vi.mock('@/store', async () => {
 })
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
-    state.testRuntimeOwner ?? null,
   getExecutionHostIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
     state.testRuntimeOwner ? `runtime:${state.testRuntimeOwner}` : 'local'
 }))
diff --git a/src/renderer/src/components/browser-pane/assemble-chrome/browser-deferred-lifecycle.test.tsx b/src/renderer/src/components/browser-pane/assemble-chrome/browser-deferred-lifecycle.test.tsx
index 0d1e0b08db1..ffaddf3cff8 100644
--- a/src/renderer/src/components/browser-pane/assemble-chrome/browser-deferred-lifecycle.test.tsx
+++ b/src/renderer/src/components/browser-pane/assemble-chrome/browser-deferred-lifecycle.test.tsx
@@ -35,7 +35,6 @@ vi.mock('@/store', async () => {
   }
 })
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: () => null,
   runtimeEnvironmentIdWithLegacyFallbackUnlessTwin: () => null,
   getExecutionHostIdForWorktree: () => mocks.executionHostId
 }))
diff --git a/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.test.ts b/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.test.ts
index b5f862d3a09..498d8fbb28e 100644
--- a/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.test.ts
+++ b/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.test.ts
@@ -63,26 +63,14 @@ vi.mock('@/store', () => ({
       },
       getKnownWorktreeById: () =>
         mocks.worktreePath === null ? undefined : { id: 'wt-1', path: mocks.worktreePath },
-      ...(mocks.twin
-        ? {
-            repos: [
-              { id: 'repo', executionHostId: 'local' },
-              { id: 'repo', connectionId: 'box', executionHostId: 'ssh:box' }
-            ],
-            worktreesByRepo: {
-              repo: [
-                { id: 'repo::/srv/repo', repoId: 'repo', hostId: 'local' },
-                { id: 'repo::/srv/repo', repoId: 'repo', hostId: 'ssh:box' }
-              ]
-            }
-          }
-        : {}),
+      ...(mocks.twin ? localAndSshTwinRows('repo', 'repo::/srv/repo') : {}),
       openFile: mocks.openFile
     })
   }
 }))
 
 import { openDocPreviewExternally, openDocPreviewSource } from './doc-preview-document-actions'
+import { localAndSshTwinRows } from '@/lib/workspace-twin-rows.test-fixture'
 
 const REMOTE_DOCUMENT = {
   filePath: '/root/demo/report/index.html',
diff --git a/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.ts b/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.ts
index 2828ae45d30..7fd8309f01e 100644
--- a/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.ts
+++ b/src/renderer/src/components/browser-pane/workspace-doc/doc-preview-document-actions.ts
@@ -3,7 +3,7 @@ import { toast } from 'sonner'
 import { translate } from '@/i18n/i18n'
 import { getConnectionIdForFileFromState } from '@/lib/connection-owner-resolution'
 import { runtimeEnvironmentIdWithLegacyFallbackUnlessTwin } from '@/lib/worktree-runtime-owner'
-import { resolveOwner } from '@/lib/resolve-owner'
+import { isTwinWorkspace } from '@/lib/resolve-owner'
 import { detectLanguage } from '@/lib/language-detect'
 import {
   buildWorkspaceFileContextForFile,
@@ -81,7 +81,7 @@ export function openDocPreviewExternally(document: DocPreviewDocument): void {
     runtimeEnvironmentId === null &&
     worktreeRoot !== null &&
     // Why: a twin reads as "no server", which is not proof this machine holds the file.
-    resolveOwner(state, { workspaceId: document.worktreeId }).kind !== 'ambiguous'
+    !isTwinWorkspace(state, document.worktreeId)
   if (ownedByThisMachine && canClientOsOpenWorkspaceFile(fileContext)) {
     void window.api.shell.openFilePath(document.filePath, LOCAL_EXECUTION_HOST_ID)
     return
diff --git a/src/renderer/src/components/native-chat/StructuredAgentSessionStatusBridge.test.tsx b/src/renderer/src/components/native-chat/StructuredAgentSessionStatusBridge.test.tsx
index 97d257ad0b5..06113cae6b1 100644
--- a/src/renderer/src/components/native-chat/StructuredAgentSessionStatusBridge.test.tsx
+++ b/src/renderer/src/components/native-chat/StructuredAgentSessionStatusBridge.test.tsx
@@ -46,8 +46,6 @@ vi.mock('@/store', async () => {
 })
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
-    state.testRuntimeOwner ?? null,
   getExecutionHostIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
     state.testRuntimeOwner ? `runtime:${state.testRuntimeOwner}` : 'local'
 }))
diff --git a/src/renderer/src/components/native-chat/native-chat-runtime-owner.ts b/src/renderer/src/components/native-chat/native-chat-runtime-owner.ts
index 3dffabd0234..dd5b6558119 100644
--- a/src/renderer/src/components/native-chat/native-chat-runtime-owner.ts
+++ b/src/renderer/src/components/native-chat/native-chat-runtime-owner.ts
@@ -26,14 +26,18 @@ export function selectNativeChatRuntimeEnvironmentId(
   state: NativeChatRuntimeOwnerState,
   terminalTabId: string
 ): string | null {
-  const worktreeId = findTerminalTabWorktreeId(state.tabsByWorktree, terminalTabId)
-  return worktreeId ? runtimeEnvironmentIdWithLegacyFallbackUnlessTwin(state, worktreeId) : null
+  return runtimeEnvironmentIdWithLegacyFallbackUnlessTwin(
+    state,
+    findTerminalTabWorktreeId(state.tabsByWorktree, terminalTabId)
+  )
 }
 
 export function createNativeChatRuntimeSelector(terminalTabId: string) {
   const selectOwner = createNativeChatTabOwnerSelector(terminalTabId)
   return (state: NativeChatRuntimeOwnerState): string | null => {
-    const worktreeId = selectOwner({ tabsByWorktree: state.tabsByWorktree })
-    return worktreeId ? runtimeEnvironmentIdWithLegacyFallbackUnlessTwin(state, worktreeId) : null
+    return runtimeEnvironmentIdWithLegacyFallbackUnlessTwin(
+      state,
+      selectOwner({ tabsByWorktree: state.tabsByWorktree })
+    )
   }
 }
diff --git a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-clock.test.tsx b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-clock.test.tsx
index a52fd0897c7..e47ebea74ee 100644
--- a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-clock.test.tsx
+++ b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-clock.test.tsx
@@ -38,8 +38,6 @@ vi.mock('@/store', async () => {
 })
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
-    state.testRuntimeOwner ?? null,
   getExecutionHostIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
     state.testRuntimeOwner ? `runtime:${state.testRuntimeOwner}` : 'local'
 }))
diff --git a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-failed-start.test.tsx b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-failed-start.test.tsx
index 1f25263f53a..14fda1ba9d2 100644
--- a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-failed-start.test.tsx
+++ b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-failed-start.test.tsx
@@ -52,7 +52,6 @@ vi.mock('@/store', async () => {
 vi.mock('sonner', () => ({ toast: { error: vi.fn(), message: vi.fn() } }))
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: () => null,
   getExecutionHostIdForWorktree: () => 'local'
 }))
 
diff --git a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-stopping.test.tsx b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-stopping.test.tsx
index fc1fc8430c3..36ddd24817c 100644
--- a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-stopping.test.tsx
+++ b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-stopping.test.tsx
@@ -35,8 +35,6 @@ vi.mock('@/store', async () => {
 })
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
-    state.testRuntimeOwner ?? null,
   getExecutionHostIdForWorktree: (state: { testRuntimeOwner?: string | null }) =>
     state.testRuntimeOwner ? `runtime:${state.testRuntimeOwner}` : 'local'
 }))
diff --git a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-unconfirmed-start.test.tsx b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-unconfirmed-start.test.tsx
index ef0bc1215cf..784039a0e45 100644
--- a/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-unconfirmed-start.test.tsx
+++ b/src/renderer/src/components/native-chat/structured-agent-session-status-bridge-unconfirmed-start.test.tsx
@@ -53,7 +53,6 @@ vi.mock('@/store', async () => {
 vi.mock('sonner', () => ({ toast: { error: vi.fn(), message: vi.fn() } }))
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: () => null,
   getExecutionHostIdForWorktree: () => 'local'
 }))
 
diff --git a/src/renderer/src/components/native-chat/structured-child-records-switch.test.tsx b/src/renderer/src/components/native-chat/structured-child-records-switch.test.tsx
index ad5fb208099..7f05ebd304a 100644
--- a/src/renderer/src/components/native-chat/structured-child-records-switch.test.tsx
+++ b/src/renderer/src/components/native-chat/structured-child-records-switch.test.tsx
@@ -23,7 +23,6 @@ import type { TerminalTab } from '../../../../shared/terminal-tab-types'
 import { isExplicitAgentStatusFresh } from '@/lib/pane-agent-evidence'
 import type { AppState } from '@/store/types'
 import type * as RuntimeRpcClientModule from '@/runtime/runtime-rpc-client'
-import type * as WorktreeRuntimeOwnerModule from '@/lib/worktree-runtime-owner'
 
 type TestStore = {
   getState: () => AppState
@@ -52,12 +51,6 @@ vi.mock('@/store', async () => {
   return { useAppStore }
 })
 
-// Partial: the status projection also resolves each chat's owner from the worktree.
-vi.mock('@/lib/worktree-runtime-owner', async (importOriginal) => ({
-  ...(await importOriginal<typeof WorktreeRuntimeOwnerModule>()),
-  getRuntimeEnvironmentIdForWorktree: () => null
-}))
-
 vi.mock('@/runtime/runtime-rpc-client', async (importOriginal) => ({
   ...(await importOriginal<typeof RuntimeRpcClientModule>()),
   runtimeEnvironmentSupportsCapability: vi.fn(async () => true)
diff --git a/src/renderer/src/components/right-sidebar/file-explorer-operation-owner.ts b/src/renderer/src/components/right-sidebar/file-explorer-operation-owner.ts
index 8a3b284e3d0..570cb831ad2 100644
--- a/src/renderer/src/components/right-sidebar/file-explorer-operation-owner.ts
+++ b/src/renderer/src/components/right-sidebar/file-explorer-operation-owner.ts
@@ -80,16 +80,7 @@ export function getFileExplorerOperationOwnerFromState(
   if (explicitOwner?.kind === 'ambiguous') {
     return { kind: 'unresolved' }
   }
-  const connectionId = getConnectionIdFromState(state, worktreeId ?? null)
-  const explicitRuntimeEnvironmentId = explicitOwner?.environmentId ?? null
-  // Why: global runtime focus is not ownership evidence while SSH/local
-  // metadata is unresolved; destructive actions must wait for explicit provenance.
-  if (connectionId === undefined && explicitRuntimeEnvironmentId === null) {
-    return { kind: 'unresolved' }
-  }
-  // Why: inferred SSH ownership outranks a projected runtime owner, but an explicit
-  // workspace runtime still owns its files.
-  const runtimeEnvironmentId = explicitRuntimeEnvironmentId?.trim()
+  const runtimeEnvironmentId = explicitOwner?.environmentId?.trim()
   if (runtimeEnvironmentId) {
     return {
       kind: 'runtime',
@@ -97,6 +88,9 @@ export function getFileExplorerOperationOwnerFromState(
       executionHostId: toRuntimeExecutionHostId(runtimeEnvironmentId)
     }
   }
+  const connectionId = getConnectionIdFromState(state, worktreeId ?? null)
+  // Why: global runtime focus is not ownership evidence while SSH/local
+  // metadata is unresolved; destructive actions must wait for explicit provenance.
   if (connectionId === undefined) {
     return { kind: 'unresolved' }
   }
diff --git a/src/renderer/src/components/right-sidebar/useFileSearchRunner.test.tsx b/src/renderer/src/components/right-sidebar/useFileSearchRunner.test.tsx
index 2f46e710715..227b209c870 100644
--- a/src/renderer/src/components/right-sidebar/useFileSearchRunner.test.tsx
+++ b/src/renderer/src/components/right-sidebar/useFileSearchRunner.test.tsx
@@ -4,6 +4,7 @@ import { act, renderHook } from '@testing-library/react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import type { SearchResult } from '../../../../shared/code-search-types'
 import { useFileSearchRunner } from './useFileSearchRunner'
+import { localAndSshTwinRows } from '@/lib/workspace-twin-rows.test-fixture'
 
 const mocks = vi.hoisted(() => ({
   getConnectionId: vi.fn(),
@@ -105,16 +106,7 @@ describe('useFileSearchRunner result ownership', () => {
     const worktreeId = 'twin-repo::/repo'
     const state = {
       settings: { activeRuntimeEnvironmentId: 'ambient-runtime-b' },
-      repos: [
-        { id: 'twin-repo', executionHostId: 'local' },
-        { id: 'twin-repo', connectionId: 'box', executionHostId: 'ssh:box' }
-      ],
-      worktreesByRepo: {
-        'twin-repo': [
-          { id: worktreeId, repoId: 'twin-repo', hostId: 'local' },
-          { id: worktreeId, repoId: 'twin-repo', hostId: 'ssh:box' }
-        ]
-      },
+      ...localAndSshTwinRows('twin-repo', worktreeId),
       fileSearchStateByWorktree: { [worktreeId]: {} }
     }
     const { hook, updates } = renderSearchRunner(state, worktreeId)
diff --git a/src/renderer/src/components/right-sidebar/useFileSearchRunner.ts b/src/renderer/src/components/right-sidebar/useFileSearchRunner.ts
index 964ab14dd97..1002ac2e93b 100644
--- a/src/renderer/src/components/right-sidebar/useFileSearchRunner.ts
+++ b/src/renderer/src/components/right-sidebar/useFileSearchRunner.ts
@@ -16,7 +16,7 @@ import {
   getExecutionHostIdForWorktree,
   runtimeEnvironmentIdWithLegacyFallbackUnlessTwin
 } from '@/lib/worktree-runtime-owner'
-import { resolveOwner } from '@/lib/resolve-owner'
+import { isTwinWorkspace } from '@/lib/resolve-owner'
 import type { SearchResult } from '../../../../shared/code-search-types'
 import { runtimeTargetForOwnerEnvironment } from '@/runtime/runtime-client-target'
 
@@ -51,11 +51,7 @@ export function useFileSearchRunner({
     getExecutionHostIdForWorktree(state, activeWorktreeId)
   )
   // Why: a workspace two hosts publish names no owner, so either host's results would mislead.
-  const ownerIsTwin = useAppStore(
-    (state) =>
-      !!activeWorktreeId &&
-      resolveOwner(state, { workspaceId: activeWorktreeId }).kind === 'ambiguous'
-  )
+  const ownerIsTwin = useAppStore((state) => isTwinWorkspace(state, activeWorktreeId))
   const searchTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
   // Why: runtime searches can finish out of order; ids keep stale results
   // from overwriting the newest query state.
diff --git a/src/renderer/src/components/tab-group/useTabGroupTabCloseCommands.structured-session.test.ts b/src/renderer/src/components/tab-group/useTabGroupTabCloseCommands.structured-session.test.ts
index fd2af0f8f87..961fa7c2e45 100644
--- a/src/renderer/src/components/tab-group/useTabGroupTabCloseCommands.structured-session.test.ts
+++ b/src/renderer/src/components/tab-group/useTabGroupTabCloseCommands.structured-session.test.ts
@@ -63,8 +63,6 @@ vi.mock('../../runtime/web-runtime-session-environment', () => ({
   isWebRuntimeSessionActive: vi.fn(() => false)
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({ getRuntimeEnvironmentIdForWorktree: () => null }))
-
 vi.mock('@/runtime/remote-browser-tab-ownership', () => ({
   browserWorkspaceHasRemoteOwner: () => false
 }))
diff --git a/src/renderer/src/components/terminal-workspace-keydown.test.ts b/src/renderer/src/components/terminal-workspace-keydown.test.ts
index fdebeabb2b7..1b5471b1dd9 100644
--- a/src/renderer/src/components/terminal-workspace-keydown.test.ts
+++ b/src/renderer/src/components/terminal-workspace-keydown.test.ts
@@ -62,7 +62,6 @@ vi.mock('@/runtime/runtime-rpc-client', () => ({ callRuntimeRpc: mocks.callRunti
 vi.mock('@/lib/structured-agent-session-launch', () => ({
   cancelStructuredAgentLaunch: mocks.cancelStructuredAgentLaunch
 }))
-vi.mock('@/lib/worktree-runtime-owner', () => ({ getRuntimeEnvironmentIdForWorktree: () => null }))
 vi.mock('@/runtime/runtime-worktree-selector', () => ({
   toRuntimeWorktreeSelector: (id: string) => `id:${id}`
 }))
diff --git a/src/renderer/src/lib/file-preview.test.ts b/src/renderer/src/lib/file-preview.test.ts
index a40a1db8afa..4d85c691553 100644
--- a/src/renderer/src/lib/file-preview.test.ts
+++ b/src/renderer/src/lib/file-preview.test.ts
@@ -6,11 +6,8 @@ import {
   openFileInBrowserTab,
   openFilePreviewToSide
 } from './file-preview'
-import {
-  getWorkspaceFileBrowserOpenTarget,
-  REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE,
-  TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE
-} from './workspace-file-browser-open-target'
+import { TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE } from './workspace-file-browser-open-target'
+import { localAndSshTwinRows } from './workspace-twin-rows.test-fixture'
 import { folderWorkspaceKey } from '../../../shared/workspace-scope'
 import { useAppStore } from '@/store'
 
@@ -76,16 +73,12 @@ vi.mock('@/store', () => ({
       getKnownWorktreeById: () => ({ id: 'wt-1', path: '/srv/repo' }),
       groupsByWorktree: {},
       layoutByWorktree: mocks.layoutByWorktree,
-      repos: [
-        { id: 'repo-1', connectionId: mocks.connectionId },
-        ...(mocks.twin ? [{ id: 'repo-1', connectionId: 'box', executionHostId: 'ssh:box' }] : [])
-      ],
-      worktreesByRepo: {
-        'repo-1': [
-          { id: 'wt-1', repoId: 'repo-1', ...(mocks.twin ? { hostId: 'local' } : {}) },
-          ...(mocks.twin ? [{ id: 'wt-1', repoId: 'repo-1', hostId: 'ssh:box' }] : [])
-        ]
-      }
+      ...(mocks.twin
+        ? localAndSshTwinRows('repo-1', 'wt-1')
+        : {
+            repos: [{ id: 'repo-1', connectionId: mocks.connectionId }],
+            worktreesByRepo: { 'repo-1': [{ id: 'wt-1', repoId: 'repo-1' }] }
+          })
     })
   }
 }))
@@ -100,6 +93,7 @@ beforeEach(() => {
   mocks.browserPagesByWorkspace = {}
   mocks.unifiedTabsByWorktree = {}
   mocks.activeWorktreeId = 'wt-1'
+  mocks.twin = false
 })
 
 /**
@@ -484,47 +478,7 @@ describe('canShowWorkspaceFileBrowserAction', () => {
   })
 })
 
-describe('getWorkspaceFileBrowserOpenTarget', () => {
-  it('returns a reusable browser navigation target for local files', () => {
-    expect(
-      getWorkspaceFileBrowserOpenTarget({
-        filePath: 'C:\\repo\\demo page.html',
-        worktreeId: 'wt-1'
-      })
-    ).toEqual({
-      status: 'ready',
-      url: 'file:///C:/repo/demo%20page.html',
-      title: 'demo page.html'
-    })
-  })
-
-  it('still refuses remote files, which have no local file URL', () => {
-    mocks.connectionId = 'ssh-1'
-
-    expect(
-      getWorkspaceFileBrowserOpenTarget({
-        filePath: '/home/alice/report.html',
-        worktreeId: 'wt-1'
-      })
-    ).toEqual({
-      status: 'unsupported',
-      reason: 'remote-worktree',
-      message: REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE
-    })
-  })
-
-  it('refuses a file:// URL for a project two hosts publish, naming why', () => {
-    mocks.twin = true
-    expect(
-      getWorkspaceFileBrowserOpenTarget({ filePath: '/srv/repo/report.html', worktreeId: 'wt-1' })
-    ).toEqual({
-      status: 'unsupported',
-      reason: 'remote-worktree',
-      message: TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE
-    })
-    mocks.twin = false
-  })
-
+describe('getWorkspaceFilePreviewPlan', () => {
   it('plans no local browser tab for a project two hosts publish', () => {
     mocks.twin = true
     expect(
@@ -534,21 +488,6 @@ describe('getWorkspaceFileBrowserOpenTarget', () => {
       message: TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE,
       reason: 'no-channel'
     })
-    mocks.twin = false
-  })
-
-  it('refuses paired files even when their connection ID is null', () => {
-    mocks.environmentId = 'managed-host'
-    expect(
-      getWorkspaceFileBrowserOpenTarget({
-        filePath: '/srv/repo/report.html',
-        worktreeId: 'wt-1'
-      })
-    ).toEqual({
-      status: 'unsupported',
-      reason: 'remote-worktree',
-      message: REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE
-    })
   })
 })
 
diff --git a/src/renderer/src/lib/file-preview.ts b/src/renderer/src/lib/file-preview.ts
index 2bbf3be9970..14965e2cc50 100644
--- a/src/renderer/src/lib/file-preview.ts
+++ b/src/renderer/src/lib/file-preview.ts
@@ -8,7 +8,7 @@ import { basename, getRelativePathInsideRoot } from '@/lib/path'
 import { getConnectionIdForFileFromState } from '@/lib/connection-owner-resolution'
 import { activateBrowserWorkspaceTab } from '@/lib/browser-workspace-tab-activation'
 import { runtimeEnvironmentIdWithLegacyFallbackUnlessTwin } from '@/lib/worktree-runtime-owner'
-import { resolveOwner } from '@/lib/resolve-owner'
+import { isTwinWorkspace } from '@/lib/resolve-owner'
 import {
   REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE,
   TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE
@@ -56,7 +56,7 @@ export function getWorkspaceFilePreviewPlan(
   filePath: string
 ): WorkspaceFilePreviewPlan {
   // Why: a twin reads as "no server" below, which would open this machine's copy of the path.
-  if (resolveOwner(state, { workspaceId: worktreeId }).kind === 'ambiguous') {
+  if (isTwinWorkspace(state, worktreeId)) {
     return {
       status: 'unsupported',
       message: TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE,
diff --git a/src/renderer/src/lib/launch-agent-structured-chat-guard.test.ts b/src/renderer/src/lib/launch-agent-structured-chat-guard.test.ts
index 6b46b1e5cad..ee3898257dd 100644
--- a/src/renderer/src/lib/launch-agent-structured-chat-guard.test.ts
+++ b/src/renderer/src/lib/launch-agent-structured-chat-guard.test.ts
@@ -178,7 +178,6 @@ vi.mock('@/runtime/local-runtime-capabilities', () => ({
 vi.mock('@/lib/worktree-runtime-owner', () => ({
   getExecutionHostIdForWorktree: () =>
     store.repos[0]?.connectionId ? `ssh:${store.repos[0].connectionId}` : 'local',
-  getRuntimeEnvironmentIdForWorktree: () => null,
   runtimeEnvironmentIdWithLegacyFallbackUnlessTwin: () => null
 }))
 vi.mock('@/runtime/structured-agent-session-client', () => ({
diff --git a/src/renderer/src/lib/resolve-owner.ts b/src/renderer/src/lib/resolve-owner.ts
index 6e6894d9694..4fd7b3db0f5 100644
--- a/src/renderer/src/lib/resolve-owner.ts
+++ b/src/renderer/src/lib/resolve-owner.ts
@@ -178,6 +178,14 @@ function focusFreeRouteState(state: WorktreeOperationRouteState): {
   }
 }
 
+/** Two hosts publish this workspace (or contest it), so no host-routed action may pick one. */
+export function isTwinWorkspace(
+  state: WorktreeOperationRouteState,
+  workspaceId: string | null | undefined
+): boolean {
+  return !!workspaceId && resolveOwner(state, { workspaceId }).kind === 'ambiguous'
+}
+
 /** Transport to the workspace's owner, or `null` when the rows name none or disagree. */
 export function runtimeTargetForWorkspaceOwner(
   state: WorktreeOperationRouteState,
@@ -270,13 +278,27 @@ export function isUnprovenServerSshRoute(
   ) {
     return false
   }
-  const repoId = getRepoIdFromWorktreeId(workspaceId)
-  const namesServer = (row: { id: string; hostId?: string; runtimeOwnerEnvironmentId?: string }) =>
-    row.id === workspaceId &&
-    parseExecutionHostId(row.hostId)?.id === at &&
-    row.runtimeOwnerEnvironmentId?.trim() === endpoint.environmentId
-  return !(
-    state.worktreesByRepo?.[repoId]?.some(namesServer) ||
-    state.detectedWorktreesByRepo?.[repoId]?.worktrees.some(namesServer)
+  return !someWorktreeCopy(
+    state,
+    workspaceId,
+    (row) =>
+      parseExecutionHostId(row.hostId)?.id === at &&
+      row.runtimeOwnerEnvironmentId?.trim() === endpoint.environmentId
+  )
+}
+
+type WorktreeCopy = { hostId?: string; runtimeOwnerEnvironmentId?: string }
+
+/** Whether a listed or detected row with this worktree id satisfies `matches`. */
+export function someWorktreeCopy(
+  state: Pick<WorktreeOperationRouteState, 'worktreesByRepo' | 'detectedWorktreesByRepo'>,
+  worktreeId: string,
+  matches: (row: WorktreeCopy) => boolean
+): boolean {
+  const repoId = getRepoIdFromWorktreeId(worktreeId)
+  const copyMatches = (row: WorktreeCopy & { id: string }) => row.id === worktreeId && matches(row)
+  return Boolean(
+    state.worktreesByRepo?.[repoId]?.some(copyMatches) ||
+    state.detectedWorktreesByRepo?.[repoId]?.worktrees.some(copyMatches)
   )
 }
diff --git a/src/renderer/src/lib/startup-draft-input-kind.test.ts b/src/renderer/src/lib/startup-draft-input-kind.test.ts
index 0f4dc8ffcba..0f9127459ad 100644
--- a/src/renderer/src/lib/startup-draft-input-kind.test.ts
+++ b/src/renderer/src/lib/startup-draft-input-kind.test.ts
@@ -22,8 +22,6 @@ vi.mock('@/store', () => ({
   }
 }))
 
-vi.mock('./worktree-runtime-owner', () => ({ getRuntimeEnvironmentIdForWorktree: () => null }))
-
 vi.mock('./agent-draft-readiness', () => ({
   waitForAgentDraftInputReady: async () => true
 }))
diff --git a/src/renderer/src/lib/workspace-file-browser-open-target.test.ts b/src/renderer/src/lib/workspace-file-browser-open-target.test.ts
new file mode 100644
index 00000000000..254e4a1a391
--- /dev/null
+++ b/src/renderer/src/lib/workspace-file-browser-open-target.test.ts
@@ -0,0 +1,90 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import {
+  getWorkspaceFileBrowserOpenTarget,
+  REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE,
+  TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE
+} from './workspace-file-browser-open-target'
+import { localAndSshTwinRows } from './workspace-twin-rows.test-fixture'
+
+const mocks = vi.hoisted(() => ({
+  environmentId: null as string | null,
+  connectionId: null as string | null,
+  twin: false
+}))
+
+vi.mock('@/lib/worktree-runtime-owner', () => ({
+  runtimeEnvironmentIdWithLegacyFallbackUnlessTwin: () => mocks.environmentId
+}))
+
+vi.mock('@/store', () => ({
+  useAppStore: {
+    getState: () =>
+      mocks.twin
+        ? localAndSshTwinRows('repo-1', 'wt-1')
+        : {
+            repos: [{ id: 'repo-1', connectionId: mocks.connectionId }],
+            worktreesByRepo: { 'repo-1': [{ id: 'wt-1', repoId: 'repo-1' }] }
+          }
+  }
+}))
+
+beforeEach(() => {
+  mocks.environmentId = null
+  mocks.connectionId = null
+  mocks.twin = false
+})
+
+describe('getWorkspaceFileBrowserOpenTarget', () => {
+  it('returns a reusable browser navigation target for local files', () => {
+    expect(
+      getWorkspaceFileBrowserOpenTarget({
+        filePath: 'C:\\repo\\demo page.html',
+        worktreeId: 'wt-1'
+      })
+    ).toEqual({
+      status: 'ready',
+      url: 'file:///C:/repo/demo%20page.html',
+      title: 'demo page.html'
+    })
+  })
+
+  it('still refuses remote files, which have no local file URL', () => {
+    mocks.connectionId = 'ssh-1'
+
+    expect(
+      getWorkspaceFileBrowserOpenTarget({
+        filePath: '/home/alice/report.html',
+        worktreeId: 'wt-1'
+      })
+    ).toEqual({
+      status: 'unsupported',
+      reason: 'remote-worktree',
+      message: REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE
+    })
+  })
+
+  it('refuses a file:// URL for a project two hosts publish, naming why', () => {
+    mocks.twin = true
+    expect(
+      getWorkspaceFileBrowserOpenTarget({ filePath: '/srv/repo/report.html', worktreeId: 'wt-1' })
+    ).toEqual({
+      status: 'unsupported',
+      reason: 'remote-worktree',
+      message: TWIN_FILE_BROWSER_UNSUPPORTED_MESSAGE
+    })
+  })
+
+  it('refuses paired files even when their connection ID is null', () => {
+    mocks.environmentId = 'managed-host'
+    expect(
+      getWorkspaceFileBrowserOpenTarget({
+        filePath: '/srv/repo/report.html',
+        worktreeId: 'wt-1'
+      })
+    ).toEqual({
+      status: 'unsupported',
+      reason: 'remote-worktree',
+      message: REMOTE_FILE_BROWSER_UNSUPPORTED_MESSAGE
+    })
+  })
+})
diff --git a/src/renderer/src/lib/workspace-file-browser-open-target.ts b/src/renderer/src/lib/workspace-file-browser-open-target.ts
index e5271801f09..5cf848dd31d 100644
--- a/src/renderer/src/lib/workspace-file-browser-open-target.ts
+++ b/src/renderer/src/lib/workspace-file-browser-open-target.ts
@@ -1,7 +1,7 @@
 import { absolutePathToFileUri } from '@/components/editor/markdown-internal-links'
 import { getConnectionIdForFile } from '@/lib/connection-context'
 import { basename } from '@/lib/path'
-import { resolveOwner } from '@/lib/resolve-owner'
+import { isTwinWorkspace } from '@/lib/resolve-owner'
 import { runtimeEnvironmentIdWithLegacyFallbackUnlessTwin } from '@/lib/worktree-runtime-owner'
 import { useAppStore } from '@/store'
 
@@ -30,7 +30,7 @@ export function getWorkspaceFileBrowserOpenTarget(params: {
 }): WorkspaceFileBrowserOpenTarget {
   const state = useAppStore.getState()
   // Why: a twin reads as "no server", which must not let a file:// URL open this machine's copy.
-  if (resolveOwner(state, { workspaceId: params.worktreeId }).kind === 'ambiguous') {
+  if (isTwinWorkspace(state, params.worktreeId)) {
     return {
       status: 'unsupported',
       reason: 'remote-worktree',
diff --git a/src/renderer/src/lib/workspace-twin-rows.test-fixture.ts b/src/renderer/src/lib/workspace-twin-rows.test-fixture.ts
new file mode 100644
index 00000000000..dd2162a4b87
--- /dev/null
+++ b/src/renderer/src/lib/workspace-twin-rows.test-fixture.ts
@@ -0,0 +1,23 @@
+import type { ExecutionHostId } from '../../../shared/execution-host'
+
+type TwinRepoRow = { id: string; connectionId?: string; executionHostId: ExecutionHostId }
+type TwinWorktreeRow = { id: string; repoId: string; hostId: ExecutionHostId }
+
+/** Repo and worktree rows for one project that this app and the SSH target `box` both publish. */
+export function localAndSshTwinRows(
+  repoId: string,
+  worktreeId: string
+): { repos: TwinRepoRow[]; worktreesByRepo: Record<string, TwinWorktreeRow[]> } {
+  return {
+    repos: [
+      { id: repoId, executionHostId: 'local' },
+      { id: repoId, connectionId: 'box', executionHostId: 'ssh:box' }
+    ],
+    worktreesByRepo: {
+      [repoId]: [
+        { id: worktreeId, repoId, hostId: 'local' },
+        { id: worktreeId, repoId, hostId: 'ssh:box' }
+      ]
+    }
+  }
+}
diff --git a/src/renderer/src/lib/worktree-runtime-owner.ts b/src/renderer/src/lib/worktree-runtime-owner.ts
index 989ae47c4e3..f7b6bba946e 100644
--- a/src/renderer/src/lib/worktree-runtime-owner.ts
+++ b/src/renderer/src/lib/worktree-runtime-owner.ts
@@ -22,7 +22,12 @@ import {
   getExecutionHostIdForFolderWorkspace,
   getRuntimeEnvironmentIdForFolderWorkspace
 } from './folder-workspace-runtime-owner'
-import { namedHostForOwnerRef, resolveOwner, type WorkspaceOwnerRef } from './resolve-owner'
+import {
+  namedHostForOwnerRef,
+  resolveOwner,
+  someWorktreeCopy,
+  type WorkspaceOwnerRef
+} from './resolve-owner'
 import { SELF_LOCAL_AUTHORITY, type HostAuthority } from '../../../shared/host-authority'
 import type { ExecutionHostOwnerMatch } from '../../../shared/worktree-execution-host-resolution'
 import {
@@ -249,16 +254,10 @@ function hasHostEvidence(state: WorktreeRuntimeOwnerState, workspaceId: string):
     )
   }
   const repoId = getRepoIdFromWorktreeId(workspaceId)
-  const isStampedCopy = (row: {
-    id: string
-    hostId?: string
-    runtimeOwnerEnvironmentId?: string
-  }) =>
-    row.id === workspaceId && Boolean(row.hostId?.trim() || row.runtimeOwnerEnvironmentId?.trim())
-  return Boolean(
-    state.worktreesByRepo?.[repoId]?.some(isStampedCopy) ||
-    state.detectedWorktreesByRepo?.[repoId]?.worktrees.some(isStampedCopy) ||
-    state.repos?.some((repo) => repo.id === repoId && hasRowHost(repo))
+  return (
+    someWorktreeCopy(state, workspaceId, (row) =>
+      Boolean(row.hostId?.trim() || row.runtimeOwnerEnvironmentId?.trim())
+    ) || Boolean(state.repos?.some((repo) => repo.id === repoId && hasRowHost(repo)))
   )
 }
 
diff --git a/src/renderer/src/runtime/web-runtime-browser-capability-cleanup.test.ts b/src/renderer/src/runtime/web-runtime-browser-capability-cleanup.test.ts
index 96e06d16ccd..04975ee4e9d 100644
--- a/src/renderer/src/runtime/web-runtime-browser-capability-cleanup.test.ts
+++ b/src/renderer/src/runtime/web-runtime-browser-capability-cleanup.test.ts
@@ -40,8 +40,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: vi.fn()
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({ getRuntimeEnvironmentIdForWorktree: vi.fn() }))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn()
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-client-placement.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-client-placement.test.ts
index e93f664fa39..ac34590f857 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-client-placement.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-client-placement.test.ts
@@ -36,7 +36,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -70,9 +69,6 @@ vi.mock('./web-session-tabs-sync/tracking-mappings', () => ({
 vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-failure.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-failure.test.ts
index 251aaf60f6d..4676587c579 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-failure.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-failure.test.ts
@@ -29,7 +29,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -66,10 +65,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-focus.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-focus.test.ts
index 9f8b2eb05b1..07dc0c1c007 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-focus.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-focus.test.ts
@@ -31,7 +31,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -68,10 +67,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-split-placement.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-split-placement.test.ts
index 56a741bc07f..61299f8ec31 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-split-placement.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-split-placement.test.ts
@@ -32,7 +32,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -69,10 +68,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-staged-focus.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-staged-focus.test.ts
index 625a3a46826..ae0abdd658b 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-staged-focus.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-staged-focus.test.ts
@@ -37,7 +37,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -71,9 +70,6 @@ vi.mock('./web-session-tabs-sync/tracking-mappings', () => ({
 vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-staged-hosting-intent.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-staged-hosting-intent.test.ts
index f5a55c6adde..ce20a93584e 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-staged-hosting-intent.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-staged-hosting-intent.test.ts
@@ -37,7 +37,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -71,9 +70,6 @@ vi.mock('./web-session-tabs-sync/tracking-mappings', () => ({
 vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-create-staging.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-create-staging.test.ts
index d519d51ab78..88a8b6ab678 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-create-staging.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-create-staging.test.ts
@@ -32,7 +32,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -69,10 +68,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-browser-placement-staleness.test.ts b/src/renderer/src/runtime/web-runtime-session-browser-placement-staleness.test.ts
index add36d9a4dc..f5e7113ab0a 100644
--- a/src/renderer/src/runtime/web-runtime-session-browser-placement-staleness.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-browser-placement-staleness.test.ts
@@ -36,7 +36,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -69,9 +68,6 @@ vi.mock('./web-session-tabs-sync/tracking-mappings', () => ({
 vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-tab-activate-close.test.ts b/src/renderer/src/runtime/web-runtime-session-tab-activate-close.test.ts
index edbc982b58e..1f7169502af 100644
--- a/src/renderer/src/runtime/web-runtime-session-tab-activate-close.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-tab-activate-close.test.ts
@@ -42,7 +42,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -80,10 +79,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts b/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts
index b6ba507f063..3739e91ed3f 100644
--- a/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts
@@ -31,7 +31,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -69,10 +68,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-tab-move.test.ts b/src/renderer/src/runtime/web-runtime-session-tab-move.test.ts
index 4ea4ae504e2..c02af82a55d 100644
--- a/src/renderer/src/runtime/web-runtime-session-tab-move.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-tab-move.test.ts
@@ -26,7 +26,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -64,10 +63,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-terminal-host-authority.test.ts b/src/renderer/src/runtime/web-runtime-session-terminal-host-authority.test.ts
index 5e148cdeda8..4e43146dd3a 100644
--- a/src/renderer/src/runtime/web-runtime-session-terminal-host-authority.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-terminal-host-authority.test.ts
@@ -36,7 +36,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -74,10 +73,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-terminal-legacy-create.test.ts b/src/renderer/src/runtime/web-runtime-session-terminal-legacy-create.test.ts
index 3f0d8808ded..1ddafefba8b 100644
--- a/src/renderer/src/runtime/web-runtime-session-terminal-legacy-create.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-terminal-legacy-create.test.ts
@@ -28,7 +28,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -65,10 +64,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-terminal-pane-delegation.test.ts b/src/renderer/src/runtime/web-runtime-session-terminal-pane-delegation.test.ts
index f4b4ae42f57..48b99d758d9 100644
--- a/src/renderer/src/runtime/web-runtime-session-terminal-pane-delegation.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-terminal-pane-delegation.test.ts
@@ -32,7 +32,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -73,10 +72,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session-terminal-workspace-routing.test.ts b/src/renderer/src/runtime/web-runtime-session-terminal-workspace-routing.test.ts
index c1908ab2786..5c646f56f11 100644
--- a/src/renderer/src/runtime/web-runtime-session-terminal-workspace-routing.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session-terminal-workspace-routing.test.ts
@@ -29,7 +29,6 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn()
 }))
 
@@ -64,10 +63,6 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
   trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
 }))
 
-vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
-}))
-
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
   deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
   seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
diff --git a/src/renderer/src/runtime/web-runtime-session.test.ts b/src/renderer/src/runtime/web-runtime-session.test.ts
index f735f9bfd5a..1e2964eef76 100644
--- a/src/renderer/src/runtime/web-runtime-session.test.ts
+++ b/src/renderer/src/runtime/web-runtime-session.test.ts
@@ -31,7 +31,7 @@ const mocks = vi.hoisted(() => ({
   trackTerminalPaneSplit: vi.fn(),
   deliverLaunchPromptToAgentTab: vi.fn(),
   seedNativeChatLaunchDraftForAgentTab: vi.fn(),
-  getRuntimeEnvironmentIdForWorktree: vi.fn(),
+  runtimeEnvironmentIdWithLegacyFallbackUnlessTwin: vi.fn(),
   hasMaterializedWebRuntimeBrowserPage: vi.fn(),
   recoverWebSessionTerminalOrphansBeforeApply: vi.fn(
     async (_state: unknown, snapshot: unknown) => snapshot
@@ -76,8 +76,8 @@ vi.mock('@/lib/feature-education-telemetry', () => ({
 }))
 
 vi.mock('@/lib/worktree-runtime-owner', () => ({
-  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree,
-  runtimeEnvironmentIdWithLegacyFallbackUnlessTwin: mocks.getRuntimeEnvironmentIdForWorktree
+  runtimeEnvironmentIdWithLegacyFallbackUnlessTwin:
+    mocks.runtimeEnvironmentIdWithLegacyFallbackUnlessTwin
 }))
 
 vi.mock('@/lib/agent-launch-prompt-delivery', () => ({