fix(app): retain workspace explorer pane

Desktop workspaces need a stable hidden explorer pane so setup and pull-request tabs have a consistent destination without changing the active pane. Mobile keeps pull requests in its explorer sidebar.

packages/app/src/screens/workspace/workspace-screen.tsx

@@ -53,9 +53,10 @@ import { traceInstant } from "@/performance/native-trace";
 import { useSessionStore, type WorkspaceDescriptor } from "@/stores/session-store";
 import {
   collectAllTabs,
-  createDefaultLayout,
+  createWorkspaceLayoutWithExplorer,
   findPaneById,
   getFocusedBrowserId,
+  resolveExplorerPaneId,
   type WorkspaceLayout,
   useWorkspaceLayoutStore,
   useWorkspaceLayoutStoreHydrated,
@@ -1360,8 +1361,12 @@ function buildWorkspaceTerminalScopeKey(serverId: string, workspaceId: string):
   return `${serverId}:${workspaceId}`;
 }
 
-function canObservePullRequest(isRouteFocused: boolean, isGitCheckout: boolean): boolean {
-  return isRouteFocused && isGitCheckout;
+function canObservePullRequest(
+  isRouteFocused: boolean,
+  isGitCheckout: boolean,
+  isCompact: boolean,
+): boolean {
+  return isRouteFocused && isGitCheckout && !isCompact && supportsDesktopPaneSplits();
 }
 
 interface ToggleWorkspaceExplorerPaneInput {
@@ -1383,15 +1388,28 @@ function toggleWorkspaceExplorerPane(input: ToggleWorkspaceExplorerPaneInput): v
   }
 
   const store = useWorkspaceLayoutStore.getState();
-  const layout = store.layoutByWorkspace[input.persistenceKey] ?? createDefaultLayout();
+  const layout =
+    store.layoutByWorkspace[input.persistenceKey] ?? createWorkspaceLayoutWithExplorer();
   const parentTabId = findPaneById(layout.root, layout.focusedPaneId)?.focusedTabId ?? null;
-  const explorerPaneId = store.explorerPaneIdByWorkspace[input.persistenceKey] ?? null;
+  const explorerPaneId = resolveExplorerPaneId(
+    layout,
+    store.explorerPaneIdByWorkspace[input.persistenceKey],
+  );
   const explorerPane = findPaneById(layout.root, explorerPaneId);
   if (explorerPane) {
     if (explorerPane.hidden === true) {
       store.showPane(input.persistenceKey, explorerPane.id);
     } else {
       store.hidePane(input.persistenceKey, explorerPane.id);
+      return;
+    }
+    if (explorerPane.tabIds.length === 0) {
+      const tabId = parentTabId
+        ? store.openChildTabFocused(input.persistenceKey, { kind: "working_diff" }, parentTabId)
+        : store.openTabFocused(input.persistenceKey, { kind: "working_diff" });
+      if (tabId) {
+        store.moveTabToPane(input.persistenceKey, tabId, explorerPane.id);
+      }
     }
     return;
   }
@@ -1415,8 +1433,10 @@ function isWorkspaceExplorerPaneOpen(
   if (!persistenceKey) {
     return false;
   }
-  const paneId = state.explorerPaneIdByWorkspace[persistenceKey];
   const layout = state.layoutByWorkspace[persistenceKey];
+  const paneId = layout
+    ? resolveExplorerPaneId(layout, state.explorerPaneIdByWorkspace[persistenceKey])
+    : null;
   const pane = paneId && layout ? findPaneById(layout.root, paneId) : null;
   return Boolean(pane && pane.hidden !== true);
 }
@@ -1706,7 +1726,7 @@ function WorkspaceScreenContent({
     workspaceKey: persistenceKey,
     serverId: normalizedServerId,
     cwd: workspaceDirectory,
-    enabled: canObservePullRequest(isRouteFocused, isGitCheckout),
+    enabled: canObservePullRequest(isRouteFocused, isGitCheckout, isMobile),
   });
 
   const isCompactExplorerOpen = usePanelStore((state) =>
@@ -1785,6 +1805,12 @@ function WorkspaceScreenContent({
   const openWorkspaceTabInBackground = useWorkspaceLayoutStore(
     (state) => state.openTabInBackground,
   );
+  const openWorkspaceTabInExplorerPaneBackground = useWorkspaceLayoutStore(
+    (state) => state.openTabInExplorerPaneBackground,
+  );
+  const openWorkspaceTabInExplorerPaneFocused = useWorkspaceLayoutStore(
+    (state) => state.openTabInExplorerPaneFocused,
+  );
   const focusWorkspaceTab = useWorkspaceLayoutStore((state) => state.focusTab);
   const closeWorkspaceTab = useWorkspaceLayoutStore((state) => state.closeTab);
   const unpinWorkspaceAgent = useWorkspaceLayoutStore((state) => state.unpinAgent);
@@ -1994,7 +2020,6 @@ function WorkspaceScreenContent({
       ),
     [normalizedWorkspaceId, uiTabs],
   );
-
   const navigateToTabId = useCallback(
     function navigateToTabId(tabId: string) {
       if (!tabId || !persistenceKey) {
@@ -2020,6 +2045,64 @@ function WorkspaceScreenContent({
   const emptyWorkspaceSeedRef = useRef<string | null>(null);
   const autoOpenedSetupTabWorkspaceRef = useRef<string | null>(null);
 
+  useEffect(() => {
+    if (!isRouteFocused) {
+      return;
+    }
+    if (!persistenceKey) {
+      return;
+    }
+    if (!workspaceSetupSnapshot || !showWorkspaceSetup) {
+      if (autoOpenedSetupTabWorkspaceRef.current === persistenceKey) {
+        autoOpenedSetupTabWorkspaceRef.current = null;
+      }
+      return;
+    }
+
+    const snapshotAge = Date.now() - workspaceSetupSnapshot.updatedAt;
+    const shouldAutoOpen =
+      workspaceSetupSnapshot.status === "running" ||
+      snapshotAge <= WORKSPACE_SETUP_AUTO_OPEN_WINDOW_MS;
+    if (!shouldAutoOpen) {
+      return;
+    }
+    if (hasSetupTab) {
+      autoOpenedSetupTabWorkspaceRef.current = persistenceKey;
+      return;
+    }
+    if (autoOpenedSetupTabWorkspaceRef.current === persistenceKey) {
+      return;
+    }
+
+    const target = normalizeWorkspaceTabTarget({
+      kind: "setup",
+      workspaceId: normalizedWorkspaceId,
+    });
+    if (!target) {
+      return;
+    }
+
+    const tabId =
+      isMobile || !supportsDesktopPaneSplits()
+        ? openWorkspaceTabInBackground(persistenceKey, target)
+        : openWorkspaceTabInExplorerPaneBackground(persistenceKey, target);
+    if (!tabId) {
+      return;
+    }
+
+    autoOpenedSetupTabWorkspaceRef.current = persistenceKey;
+  }, [
+    hasSetupTab,
+    isMobile,
+    isRouteFocused,
+    normalizedWorkspaceId,
+    openWorkspaceTabInBackground,
+    openWorkspaceTabInExplorerPaneBackground,
+    persistenceKey,
+    showWorkspaceSetup,
+    workspaceSetupSnapshot,
+  ]);
+
   useEffect(() => {
     if (!isRouteFocused || !client || !normalizedServerId || !normalizedWorkspaceId) {
       return;
@@ -2075,59 +2158,6 @@ function WorkspaceScreenContent({
     workspaceAgentVisibility.activeAgentIds.size,
   ]);
 
-  useEffect(() => {
-    if (!isRouteFocused) {
-      return;
-    }
-    if (!persistenceKey) {
-      return;
-    }
-    if (!workspaceSetupSnapshot || !showWorkspaceSetup) {
-      if (autoOpenedSetupTabWorkspaceRef.current === persistenceKey) {
-        autoOpenedSetupTabWorkspaceRef.current = null;
-      }
-      return;
-    }
-
-    const snapshotAge = Date.now() - workspaceSetupSnapshot.updatedAt;
-    const shouldAutoOpen =
-      workspaceSetupSnapshot.status === "running" ||
-      snapshotAge <= WORKSPACE_SETUP_AUTO_OPEN_WINDOW_MS;
-    if (!shouldAutoOpen) {
-      return;
-    }
-    if (hasSetupTab) {
-      autoOpenedSetupTabWorkspaceRef.current = persistenceKey;
-      return;
-    }
-    if (autoOpenedSetupTabWorkspaceRef.current === persistenceKey) {
-      return;
-    }
-
-    const target = normalizeWorkspaceTabTarget({
-      kind: "setup",
-      workspaceId: normalizedWorkspaceId,
-    });
-    if (!target) {
-      return;
-    }
-
-    const tabId = openWorkspaceTabInBackground(persistenceKey, target);
-    if (!tabId) {
-      return;
-    }
-
-    autoOpenedSetupTabWorkspaceRef.current = persistenceKey;
-  }, [
-    hasSetupTab,
-    isRouteFocused,
-    normalizedWorkspaceId,
-    openWorkspaceTabInBackground,
-    persistenceKey,
-    showWorkspaceSetup,
-    workspaceSetupSnapshot,
-  ]);
-
   const handleOpenFileFromExplorer = useCallback(
     function handleOpenFileFromExplorer(filePath: string) {
       if (!persistenceKey) {
@@ -2704,8 +2734,18 @@ function WorkspaceScreenContent({
     if (!target) {
       return;
     }
+    if (isMobile || !supportsDesktopPaneSplits()) {
       openWorkspaceTabFocused(persistenceKey, target);
-  }, [normalizedWorkspaceId, openWorkspaceTabFocused, persistenceKey]);
+      return;
+    }
+    openWorkspaceTabInExplorerPaneFocused(persistenceKey, { target });
+  }, [
+    isMobile,
+    normalizedWorkspaceId,
+    openWorkspaceTabFocused,
+    openWorkspaceTabInExplorerPaneFocused,
+    persistenceKey,
+  ]);
 
   const handleBulkCloseTabs = useCallback(
     async (input: { tabsToClose: WorkspaceTabDescriptor[]; title: string; logLabel: string }) => {

packages/app/src/stores/workspace-layout-actions.ts

@@ -140,6 +140,7 @@ interface ReorderFocusedPaneTabsInLayoutInput {
 interface CloseTabInLayoutInput {
   layout: WorkspaceLayout;
   tabId: string;
+  preserveEmptyPaneId?: string | null;
 }
 
 interface SplitPaneInLayoutInput {
@@ -211,6 +212,8 @@ export interface WorkspaceTabSnapshot {
 }
 
 const DEFAULT_PANE_ID = "main";
+export const DEFAULT_EXPLORER_PANE_ID = "explorer";
+const DEFAULT_LAYOUT_GROUP_ID = "workspace-root";
 
 function trimNonEmpty(value: string | null | undefined): string | null {
   if (typeof value !== "string") {
@@ -1051,6 +1054,22 @@ export function createDefaultLayout(): WorkspaceLayout {
   };
 }
 
+/** The desktop companion pane exists before it is first shown. */
+export function createWorkspaceLayoutWithExplorer(): WorkspaceLayout {
+  return {
+    root: createGroupNode({
+      id: DEFAULT_LAYOUT_GROUP_ID,
+      direction: "horizontal",
+      children: [
+        createPaneNode({ id: DEFAULT_PANE_ID }),
+        createPaneNode({ id: DEFAULT_EXPLORER_PANE_ID, hidden: true }),
+      ],
+      sizes: [0.5, 0.5],
+    }),
+    focusedPaneId: DEFAULT_PANE_ID,
+  };
+}
+
 export function insertSplit(
   root: SplitNode,
   targetPaneId: string,
@@ -1079,7 +1098,10 @@ export function removePaneFromTree(root: SplitNode, paneId: string): SplitNode {
 }
 
 export function removeTabFromTree(root: SplitNode, tabId: string): SplitNode {
-  return detachTabFromTree(asInternalNode(root), { tabId }).root;
+  return detachTabFromTree(asInternalNode(root), {
+    tabId,
+    preserveEmptyPaneId: DEFAULT_PANE_ID,
+  }).root;
 }
 
 function insertNewTabIntoFocusedPane(input: {
@@ -1182,6 +1204,9 @@ export function closeTabInLayout(input: CloseTabInLayoutInput): WorkspaceLayout
   if (!pane) {
     return null;
   }
+  const preserveEmptyPaneId =
+    input.preserveEmptyPaneId ??
+    (pane.id === DEFAULT_PANE_ID || pane.id === DEFAULT_EXPLORER_PANE_ID ? pane.id : null);
 
   const closeSuccessorTabId = getCloseSuccessorTabId({
     pane,
@@ -1190,7 +1215,10 @@ export function closeTabInLayout(input: CloseTabInLayoutInput): WorkspaceLayout
     parentTabIdByTabId: input.layout.parentTabIdByTabId,
   });
   const fallbackPaneId = findNearestSiblingPaneId(internalLayout.root, pane.id);
-  const nextRoot = removeTabFromTree(internalLayout.root, input.tabId) as SplitNodeInternal;
+  const nextRoot = detachTabFromTree(internalLayout.root, {
+    tabId: input.tabId,
+    preserveEmptyPaneId,
+  }).root;
   const parentTabIdByTabId = normalizeParentTabMap({
     raw: input.layout.parentTabIdByTabId,
     openTabIds: new Set(collectAllTabs(nextRoot).map((tab) => tab.tabId)),

packages/app/src/stores/workspace-layout-store.test.ts

@@ -22,6 +22,7 @@ import {
   collectAllTabs,
   createWorkspaceLayoutStore,
   createDefaultLayout,
+  createWorkspaceLayoutWithExplorer,
   findPaneById,
   findPaneContainingTab,
   getFocusedBrowserId,
@@ -329,7 +330,7 @@ describe("workspace-layout-store actions", () => {
     });
   });
 
-  it("keeps layouts written before split sizes were persisted", async () => {
+  it("migrates legacy layouts to include the hidden registered explorer pane", async () => {
     const legacyLayout = createDefaultLayout();
     await AsyncStorage.setItem(
       "workspace-layout-state",
@@ -342,7 +343,12 @@ describe("workspace-layout-store actions", () => {
 
     await restored.persist.rehydrate();
 
-    expect(restored.getState().layoutByWorkspace.legacy).toEqual(legacyLayout);
+    const state = restored.getState();
+    const layout = state.layoutByWorkspace.legacy;
+    const explorerPaneId = state.explorerPaneIdByWorkspace.legacy;
+    expect(findPaneById(layout.root, "main")).toBeTruthy();
+    expect(explorerPaneId).toBeTruthy();
+    expect(findPaneById(layout.root, explorerPaneId)?.hidden).toBe(true);
     expect(restored.getState().splitSizesByWorkspace).toEqual({});
     await expect(AsyncStorage.getItem("workspace-layout-state")).resolves.not.toBeNull();
   });
@@ -407,6 +413,40 @@ describe("workspace-layout-store actions", () => {
     ]);
   });
 
+  it("reveals the registered explorer pane for a first detected pull request", () => {
+    const workspaceKey = createWorkspaceKey();
+    const store = workspaceLayoutStore.getState();
+
+    store.observePullRequest(workspaceKey, "url:https://example.test/pulls/1");
+
+    const state = workspaceLayoutStore.getState();
+    const layout = state.layoutByWorkspace[workspaceKey];
+    const explorerPaneId = state.explorerPaneIdByWorkspace[workspaceKey];
+    expect(explorerPaneId).toBe("explorer");
+    expect(findPaneById(layout.root, explorerPaneId)?.hidden).toBeUndefined();
+    expect(findPaneContainingTab(layout.root, "pull_request")?.id).toBe(explorerPaneId);
+  });
+
+  it("creates setup in the hidden explorer pane without changing focus", () => {
+    const workspaceKey = createWorkspaceKey();
+    const store = workspaceLayoutStore.getState();
+    const agentTabId = store.openTabFocused(workspaceKey, { kind: "agent", agentId: "agent-1" });
+
+    const tabId = store.openTabInExplorerPaneBackground(workspaceKey, {
+      kind: "setup",
+      workspaceId: WORKSPACE_ID,
+    });
+
+    const state = workspaceLayoutStore.getState();
+    const layout = state.layoutByWorkspace[workspaceKey];
+    const explorerPaneId = state.explorerPaneIdByWorkspace[workspaceKey];
+    expect(tabId).toBe("setup_ws-main");
+    expect(layout.focusedPaneId).toBe("main");
+    expect(findPaneById(layout.root, explorerPaneId)?.hidden).toBe(true);
+    expect(findPaneById(layout.root, "main")?.focusedTabId).toBe(agentTabId);
+    expect(findPaneContainingTab(layout.root, tabId!)?.id).toBe(explorerPaneId);
+  });
+
   it("places an auto-added pull request in the registered explorer pane", () => {
     const workspaceKey = createWorkspaceKey();
     const store = workspaceLayoutStore.getState();
@@ -445,8 +485,6 @@ describe("workspace-layout-store actions", () => {
   it("opens assistant files in an ensured explorer pane and reveals it on the next open", () => {
     const workspaceKey = createWorkspaceKey();
     const store = workspaceLayoutStore.getState();
-    useWorkspaceLayoutIds("explorer");
-
     const tabId = store.openTabInExplorerPaneFocused(workspaceKey, {
       target: { kind: "file", path: "/repo/worktree/a.ts" },
       parentTabId: "agent_agent-a",
@@ -454,7 +492,7 @@ describe("workspace-layout-store actions", () => {
     const createdState = workspaceLayoutStore.getState();
     const explorerPaneId = createdState.explorerPaneIdByWorkspace[workspaceKey];
 
-    expect(explorerPaneId).toBe("pane_explorer");
+    expect(explorerPaneId).toBe("explorer");
     expect(
       findPaneContainingTab(createdState.layoutByWorkspace[workspaceKey].root, tabId!)?.id,
     ).toBe(explorerPaneId);
@@ -1276,7 +1314,7 @@ describe("workspace-layout-store actions", () => {
     expect(collectAllPanes(layout.root).map((pane) => pane.id)).toEqual(["main"]);
   });
 
-  it("splitPane enforces the maximum depth of four", () => {
+  it("splitPane preserves four user-created levels beneath the explorer split", () => {
     useWorkspaceLayoutIds(
       "11111111-1111-1111-1111-111111111111",
       "22222222-2222-2222-2222-222222222222",
@@ -1323,7 +1361,7 @@ describe("workspace-layout-store actions", () => {
     expect(pane2).toBe("pane_33333333-3333-3333-3333-333333333333");
     expect(pane3).toBe("pane_55555555-5555-5555-5555-555555555555");
     expect(pane4).toBeNull();
-    expect(getTreeDepth(layout.root)).toBe(4);
+    expect(getTreeDepth(layout.root)).toBe(5);
   });
 
   it("moveTabToPane collapses the source pane when its last tab moves out", () => {
@@ -1388,38 +1426,13 @@ describe("workspace-layout-store actions", () => {
 
     store.closeTab(workspaceKey, secondTabId!);
     const layout = workspaceLayoutStore.getState().layoutByWorkspace[workspaceKey];
-    const rootGroup = expectGroup(layout.root);
 
     expect(paneBId).toBe("pane_78787878-7878-7878-7878-787878787878");
     expect(paneCId).toBe("pane_9a9a9a9a-9a9a-9a9a-9a9a-9a9a9a9a9a9a");
     expect(layout.focusedPaneId).toBe(paneCId);
-    expect(rootGroup.group.direction).toBe("horizontal");
-    expect(rootGroup.group.children).toHaveLength(2);
-    expect(
-      rootGroup.group.children.map((child) => {
-        expect(child.kind).toBe("pane");
-        if (child.kind !== "pane") {
-          throw new Error("Expected pane child");
-        }
-        return {
-          id: child.pane.id,
-          tabIds: child.pane.tabIds,
-          focusedTabId: child.pane.focusedTabId,
-        };
-      }),
-    ).toEqual([
-      {
-        id: "main",
-        tabIds: ["file_/repo/worktree/a.ts"],
-        focusedTabId: "file_/repo/worktree/a.ts",
-      },
-      {
-        id: paneCId!,
-        tabIds: ["file_/repo/worktree/c.ts"],
-        focusedTabId: "file_/repo/worktree/c.ts",
-      },
-    ]);
-    expect(rootGroup.group.sizes).toEqual([0.5, 0.5]);
+    expect(findPaneById(layout.root, "main")?.tabIds).toEqual(["file_/repo/worktree/a.ts"]);
+    expect(findPaneById(layout.root, paneCId)?.tabIds).toEqual(["file_/repo/worktree/c.ts"]);
+    expect(findPaneById(layout.root, "explorer")?.hidden).toBe(true);
   });
 
   it("openTab focuses the existing tab instead of creating a duplicate entry", () => {
@@ -1546,17 +1559,21 @@ describe("workspace-layout-store actions", () => {
     const farRightPaneId = store.splitPane(workspaceKey, {
       tabId: c!,
       targetPaneId: rightPaneId!,
-      position: "right",
+      position: "bottom",
     });
 
     const splitRoot = workspaceLayoutStore.getState().layoutByWorkspace[workspaceKey].root;
     const splitGroup = expectGroup(splitRoot);
-    const nestedGroup = expectGroup(splitGroup.group.children[1]);
+    const nestedGroup = expectGroup(
+      splitGroup.group.children.find((child) => child.kind === "group")!,
+    );
     store.resizeSplit(workspaceKey, nestedGroup.group.id, [0.01, 0.99]);
 
     const resizedRoot = workspaceLayoutStore.getState().layoutByWorkspace[workspaceKey].root;
     const resizedGroup = expectGroup(resizedRoot);
-    const resizedNestedGroup = expectGroup(resizedGroup.group.children[1]);
+    const resizedNestedGroup = expectGroup(
+      resizedGroup.group.children.find((child) => child.kind === "group")!,
+    );
     const total = resizedNestedGroup.group.sizes.reduce((sum, size) => sum + size, 0);
 
     expect(rightPaneId).toBe("pane_eeeeeeee-eeee-eeee-eeee-eeeeeeeeeeee");
@@ -1574,7 +1591,7 @@ describe("workspace-layout-store actions", () => {
     store.closeTab(workspaceKey, tabId!);
     const layout = workspaceLayoutStore.getState().layoutByWorkspace[workspaceKey];
 
-    expect(layout).toEqual(createDefaultLayout());
+    expect(layout).toEqual(createWorkspaceLayoutWithExplorer());
   });
 
   it("keeps pinned archived agents in memory per workspace without persisting them", () => {

packages/app/src/stores/workspace-layout-store.ts

@@ -15,6 +15,8 @@ import {
   collectAllTabs,
   convertDraftToAgentInLayout,
   createDefaultLayout,
+  createWorkspaceLayoutWithExplorer,
+  DEFAULT_EXPLORER_PANE_ID,
   findPaneById,
   findPaneContainingTab,
   focusPaneInLayout,
@@ -50,6 +52,7 @@ export {
   collectAllPanes,
   collectAllTabs,
   createDefaultLayout,
+  createWorkspaceLayoutWithExplorer,
   findPaneById,
   findPaneContainingTab,
   getFocusedBrowserId,
@@ -85,6 +88,10 @@ interface WorkspaceLayoutStore {
     parentTabId: string,
   ) => string | null;
   openTabInBackground: (workspaceKey: string, target: WorkspaceTabTarget) => string | null;
+  openTabInExplorerPaneBackground: (
+    workspaceKey: string,
+    target: WorkspaceTabTarget,
+  ) => string | null;
   ensureExplorerPane: (workspaceKey: string) => EnsureExplorerPaneResult | null;
   openTabInExplorerPaneFocused: (
     workspaceKey: string,
@@ -140,7 +147,9 @@ interface WorkspaceFocusRestorationState {
   tokens: string[];
 }
 
-const MAX_TREE_DEPTH = 4;
+// The root companion split is always present for the hidden explorer pane.
+// Preserve four user-created split levels beneath it.
+const MAX_TREE_DEPTH = 5;
 
 const WorkspaceDraftTabSetupStorageSchema = z.strictObject({
   provider: z.string(),
@@ -293,7 +302,52 @@ function getWorkspaceLayout(
   state: Record<string, WorkspaceLayout>,
   workspaceKey: string,
 ): WorkspaceLayout {
-  return normalizeLayout(state[workspaceKey] ?? createDefaultLayout());
+  return normalizeLayout(state[workspaceKey] ?? createWorkspaceLayoutWithExplorer());
+}
+
+export function resolveExplorerPaneId(
+  layout: WorkspaceLayout,
+  registeredPaneId: string | null | undefined,
+): string | null {
+  const registeredPane = findPaneById(layout.root, registeredPaneId ?? null);
+  if (registeredPane) {
+    return registeredPane.id;
+  }
+  const defaultPane = findPaneById(layout.root, DEFAULT_EXPLORER_PANE_ID);
+  return defaultPane?.id ?? null;
+}
+
+function ensurePersistedExplorerPane(input: {
+  layout: WorkspaceLayout;
+  registeredPaneId: string | null | undefined;
+  ids: WorkspaceLayoutIdSource;
+}): { layout: WorkspaceLayout; paneId: string } | null {
+  const existingPaneId = resolveExplorerPaneId(input.layout, input.registeredPaneId);
+  if (existingPaneId) {
+    return { layout: input.layout, paneId: existingPaneId };
+  }
+  const targetPaneId =
+    findPaneById(input.layout.root, input.layout.focusedPaneId)?.id ??
+    collectAllPanes(input.layout.root)[0]?.id;
+  if (!targetPaneId) {
+    return null;
+  }
+  const split = splitPaneEmptyInLayout({
+    layout: input.layout,
+    targetPaneId,
+    position: "right",
+    createNodeId: input.ids.createNodeId,
+    maxTreeDepth: MAX_TREE_DEPTH,
+  });
+  if (!split) {
+    return null;
+  }
+  const hiddenLayout = setPaneHiddenInLayout({
+    layout: split.layout,
+    paneId: split.paneId,
+    hidden: true,
+  });
+  return { layout: hiddenLayout ?? split.layout, paneId: split.paneId };
 }
 
 function withoutFocusRestoration(
@@ -447,6 +501,71 @@ export function createWorkspaceLayoutStore(
 
           return result.tabId;
         },
+        openTabInExplorerPaneBackground: (workspaceKey, target) => {
+          const normalizedWorkspaceKey = trimNonEmpty(workspaceKey);
+          const normalizedTarget = normalizeWorkspaceTabTarget(target);
+          if (!normalizedWorkspaceKey || !normalizedTarget) {
+            return null;
+          }
+
+          let tabId: string | null = null;
+          set((state) => {
+            const layout = getWorkspaceLayout(state.layoutByWorkspace, normalizedWorkspaceKey);
+            const explorerPaneId = resolveExplorerPaneId(
+              layout,
+              state.explorerPaneIdByWorkspace[normalizedWorkspaceKey],
+            );
+            const explorerPane = findPaneById(layout.root, explorerPaneId);
+            if (!explorerPane) {
+              return state;
+            }
+
+            const originalFocusedPaneId = layout.focusedPaneId;
+            const revealedLayout = focusPaneInLayout({ layout, paneId: explorerPane.id }) ?? layout;
+            const result = openTabInLayoutBackground({
+              layout: revealedLayout,
+              target: normalizedTarget,
+              now: Date.now(),
+            });
+            const currentPane = findPaneContainingTab(result.layout.root, result.tabId);
+            const placedLayout =
+              currentPane?.id === explorerPane.id
+                ? result.layout
+                : (moveTabToPaneInLayout({
+                    layout: result.layout,
+                    tabId: result.tabId,
+                    toPaneId: explorerPane.id,
+                  }) ?? result.layout);
+            const restoredVisibility = explorerPane.hidden
+              ? (setPaneHiddenInLayout({
+                  layout: placedLayout,
+                  paneId: explorerPane.id,
+                  hidden: true,
+                }) ?? placedLayout)
+              : placedLayout;
+            const restoredLayout =
+              originalFocusedPaneId && originalFocusedPaneId !== explorerPane.id
+                ? (focusPaneInLayout({
+                    layout: restoredVisibility,
+                    paneId: originalFocusedPaneId,
+                  }) ?? restoredVisibility)
+                : restoredVisibility;
+
+            tabId = result.tabId;
+            return {
+              ...withoutFocusRestoration(state, normalizedWorkspaceKey),
+              explorerPaneIdByWorkspace: {
+                ...state.explorerPaneIdByWorkspace,
+                [normalizedWorkspaceKey]: explorerPane.id,
+              },
+              layoutByWorkspace: {
+                ...state.layoutByWorkspace,
+                [normalizedWorkspaceKey]: restoredLayout,
+              },
+            };
+          });
+          return tabId;
+        },
         ensureExplorerPane: (workspaceKey) => {
           const normalizedWorkspaceKey = trimNonEmpty(workspaceKey);
           if (!normalizedWorkspaceKey) {
@@ -455,9 +574,15 @@ export function createWorkspaceLayoutStore(
 
           const store = get();
           const layout = getWorkspaceLayout(store.layoutByWorkspace, normalizedWorkspaceKey);
-          const explorerPaneId = store.explorerPaneIdByWorkspace[normalizedWorkspaceKey] ?? null;
+          const explorerPaneId = resolveExplorerPaneId(
+            layout,
+            store.explorerPaneIdByWorkspace[normalizedWorkspaceKey],
+          );
           const explorerPane = findPaneById(layout.root, explorerPaneId);
           if (explorerPane) {
+            if (store.explorerPaneIdByWorkspace[normalizedWorkspaceKey] !== explorerPane.id) {
+              store.setExplorerPaneId(normalizedWorkspaceKey, explorerPane.id);
+            }
             store.focusPane(normalizedWorkspaceKey, explorerPane.id);
             return { paneId: explorerPane.id, created: false };
           }
@@ -521,11 +646,16 @@ export function createWorkspaceLayoutStore(
             }
 
             const layout = getWorkspaceLayout(state.layoutByWorkspace, normalizedWorkspaceKey);
-            const explorerPaneId = state.explorerPaneIdByWorkspace[normalizedWorkspaceKey] ?? null;
+            const explorerPaneId = resolveExplorerPaneId(
+              layout,
+              state.explorerPaneIdByWorkspace[normalizedWorkspaceKey],
+            );
             const explorerPane = findPaneById(layout.root, explorerPaneId);
-            const placementLayout = explorerPane
-              ? (focusPaneInLayout({ layout, paneId: explorerPane.id }) ?? layout)
-              : layout;
+            if (!explorerPane) {
+              return state;
+            }
+            const placementLayout =
+              focusPaneInLayout({ layout, paneId: explorerPane.id }) ?? layout;
             const result = openTabInLayoutFocused({
               layout: placementLayout,
               target: { kind: "pull_request" },
@@ -538,6 +668,10 @@ export function createWorkspaceLayoutStore(
                 ...state.acknowledgedPullRequestByWorkspace,
                 [normalizedWorkspaceKey]: normalizedIdentity,
               },
+              explorerPaneIdByWorkspace: {
+                ...state.explorerPaneIdByWorkspace,
+                [normalizedWorkspaceKey]: explorerPane.id,
+              },
               layoutByWorkspace: {
                 ...state.layoutByWorkspace,
                 [normalizedWorkspaceKey]: result.layout,
@@ -553,9 +687,20 @@ export function createWorkspaceLayoutStore(
           }
 
           set((state) => {
+            const layout = getWorkspaceLayout(state.layoutByWorkspace, normalizedWorkspaceKey);
+            const explorerPaneId = resolveExplorerPaneId(
+              layout,
+              state.explorerPaneIdByWorkspace[normalizedWorkspaceKey],
+            );
+            const closingPane = findPaneContainingTab(layout.root, normalizedTabId);
+            const preserveEmptyPaneId =
+              closingPane?.id === "main" || closingPane?.id === explorerPaneId
+                ? closingPane.id
+                : null;
             const nextLayout = closeTabInLayout({
-              layout: getWorkspaceLayout(state.layoutByWorkspace, normalizedWorkspaceKey),
+              layout,
               tabId: normalizedTabId,
+              preserveEmptyPaneId,
             });
             if (!nextLayout) {
               return state;
@@ -1252,11 +1397,30 @@ export function createWorkspaceLayoutStore(
           if (!result.success) {
             return currentState;
           }
+          const layoutByWorkspace: Record<string, WorkspaceLayout> = {};
+          const explorerPaneIdByWorkspace: Record<string, string | null> = {
+            ...result.data.explorerPaneIdByWorkspace,
+          };
+          for (const [workspaceKey, persistedLayout] of Object.entries(
+            result.data.layoutByWorkspace,
+          )) {
+            const explorer = ensurePersistedExplorerPane({
+              layout: normalizeLayout(persistedLayout),
+              registeredPaneId: explorerPaneIdByWorkspace[workspaceKey],
+              ids,
+            });
+            if (!explorer) {
+              layoutByWorkspace[workspaceKey] = normalizeLayout(persistedLayout);
+              continue;
+            }
+            layoutByWorkspace[workspaceKey] = explorer.layout;
+            explorerPaneIdByWorkspace[workspaceKey] = explorer.paneId;
+          }
           return {
             ...currentState,
-            layoutByWorkspace: result.data.layoutByWorkspace,
+            layoutByWorkspace,
             splitSizesByWorkspace: result.data.splitSizesByWorkspace ?? {},
-            explorerPaneIdByWorkspace: result.data.explorerPaneIdByWorkspace ?? {},
+            explorerPaneIdByWorkspace,
             acknowledgedPullRequestByWorkspace:
               result.data.acknowledgedPullRequestByWorkspace ?? {},
           };