fix(mobile): open a worktree on the tab the desktop is showing (#31215)

src/main/runtime/client-session-tab-selection.test.ts

@@ -130,15 +130,27 @@ describe('client session-tab selection', () => {
     expect(store.project(initial, 'device-a').activeTabId).toBe('terminal-a::leaf-a')
   })
 
-  it('does not expose host focus when initializing a new paired device', () => {
+  it('lands a device that has not picked a tab on the host focus', () => {
     const store = new ClientSessionTabSelectionStore()
-    const hostFocusedBrowser = snapshot('browser-unified')
 
-    const projected = store.project(hostFocusedBrowser, 'new-device')
+    const projected = store.project(snapshot('browser-unified'), 'new-device')
 
-    expect(projected.activeTabId).toBe('terminal-a::leaf-a')
-    expect(projected.activeGroupId).toBe('group-left')
-    expect(projected.tabs.find((tab) => tab.isActive)?.id).toBe('terminal-a::leaf-a')
+    expect(projected.activeTabId).toBe('browser-unified')
+    expect(projected.activeGroupId).toBe('group-right')
+    expect(projected.tabs.find((tab) => tab.isActive)?.id).toBe('browser-unified')
+    // A later open follows where the host moved, not the first projection.
+    expect(store.project(snapshot('terminal-a::leaf-b'), 'new-device').activeTabId).toBe(
+      'terminal-a::leaf-b'
+    )
+  })
+
+  it('keeps a device on its own pick when the host moves', () => {
+    const store = new ClientSessionTabSelectionStore()
+    store.activate(snapshot(), 'device-a', 'browser-unified')
+
+    expect(store.project(snapshot('terminal-a::leaf-b'), 'device-a').activeTabId).toBe(
+      'browser-unified'
+    )
   })
 
   it('persists activations and restores them across a store rebuild (host restart)', () => {

src/main/runtime/client-session-tab-selection.ts

@@ -193,7 +193,6 @@ export class ClientSessionTabSelectionStore {
     const statesByWorktree = this.getStatesByWorktree(clientNavigationId)
     const existingState = statesByWorktree.get(snapshot.worktree)
     const state = existingState ?? {
-      // Why: host focus is private navigation; a new paired device starts from deterministic topology instead of inheriting it.
       selection: emptyClientSessionTabSelection(),
       revision: 0,
       shouldPersist: false,
@@ -214,14 +213,18 @@ export class ClientSessionTabSelectionStore {
         snapshotVersion: snapshot.snapshotVersion + state.revision
       }
     }
-    const projected = projectClientSessionTabSelection(closed.snapshot, state.selection)
+    // Why: until the device picks a tab here, opening the worktree lands on what the host shows;
+    // clients keep their own tab while open, so this never moves a device mid-visit.
+    const selection = state.shouldPersist
+      ? state.selection
+      : deriveClientSessionTabSelection(closed.snapshot)
+    const projected = projectClientSessionTabSelection(closed.snapshot, selection)
     // Why: a browser guest process swap drops its tab for one snapshot; the topology fallback
     // must not overwrite (and persist) the device's explicit pick, or focus never returns.
     const selectionSurvived =
-      !state.selection.activeTabId ||
-      closed.snapshot.tabs.some((tab) => tab.id === state.selection.activeTabId)
+      !selection.activeTabId || closed.snapshot.tabs.some((tab) => tab.id === selection.activeTabId)
     statesByWorktree.set(snapshot.worktree, {
-      selection: selectionSurvived ? projected.selection : state.selection,
+      selection: selectionSurvived ? projected.selection : selection,
       revision: state.revision,
       shouldPersist: state.shouldPersist,
       closedTabIds: closed.retainedClosedTabIds

src/main/runtime/multi-client-navigation-isolation.integration.test.ts

@@ -807,7 +807,7 @@ describe('paired runtime navigation isolation', () => {
     )
     expect(remembered.activeTabId).toBe('client-a-tab')
     expect(remembered.tabs.find((tab) => tab.isActive)?.id).toBe('client-a-tab')
-    // Why: an unknown device must still start from deterministic topology, not inherit another device's restored state.
+    // Why: an unknown device starts from the host's view, not another device's restored state.
     const freshDevice = await restarted.listMobileSessionTabs(
       `id:${SESSION_WORKTREE_ID}`,
       'device-b'