From 668f6e05dd8aa7614036e4d8a9ef6431d5c6293a Mon Sep 17 00:00:00 2001
From: Julius Marminge <51714798+juliusmarminge@users.noreply.github.com>
Date: Tue, 27 Oct 2026 10:50:08 -0700
Subject: [PATCH] fix(web): closing the last Browser tab hides the right panel
 again

Closing the last right-panel tab hid the panel for Files, Diff and Terminal
tabs, but a Browser tab left it open on the empty "Open a surface" screen.

Cause: the close hook released the browser session before closing the tab.
Releasing drops the session from the preview store, and since #25006 the
browser-tab sync subscribes to that store directly, so it removed the tab
without hiding the panel; the store close then found nothing to close.

Fix: close the tab in the store first, then release its resources. Browser
reconciliation now also hides the panel when it removes the last
session-backed tab, so a browser closed by an agent or another client hides
it too, as file reconciliation already does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../preview/agentOpenedPreviews.test.ts        |  2 +-
 .../web/src/hooks/useRightPanelSurfaceClose.ts |  4 +++-
 apps/web/src/rightPanelStore.test.ts           | 18 ++++++++++++++++++
 apps/web/src/rightPanelStore.ts                |  6 ++++++
 4 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/apps/web/src/components/preview/agentOpenedPreviews.test.ts b/apps/web/src/components/preview/agentOpenedPreviews.test.ts
index 9464d832d7f79..f6ad67432acdd 100644
--- a/apps/web/src/components/preview/agentOpenedPreviews.test.ts
+++ b/apps/web/src/components/preview/agentOpenedPreviews.test.ts
@@ -258,7 +258,7 @@ describe("followPreviewSessions", () => {
     useRightPanelStore
       .getState()
       .byThreadKey[threadKey]?.surfaces.filter((surface) => surface.kind === "preview")
-      .map((surface) => surface.id);
+      .map((surface) => surface.id) ?? [];
 
   it("adds visible sessions as tabs and drops tabs whose session ended", () => {
     setup();
diff --git a/apps/web/src/hooks/useRightPanelSurfaceClose.ts b/apps/web/src/hooks/useRightPanelSurfaceClose.ts
index 6fc0185dbb187..294112b6ce1f9 100644
--- a/apps/web/src/hooks/useRightPanelSurfaceClose.ts
+++ b/apps/web/src/hooks/useRightPanelSurfaceClose.ts
@@ -88,8 +88,10 @@ export function useRightPanelSurfaceClose(input: {
       (left, right) => Number(left.id === activeId) - Number(right.id === activeId),
     );
     for (const surface of ordered) {
-      releaseSurfaceResources(threadRef, surface);
+      // Releasing a browser drops its session, which prunes the tab automatically; close it
+      // first so the close stays a user action that hides the panel after the last tab.
       store.closeSurface(threadRef, surface.id);
+      releaseSurfaceResources(threadRef, surface);
     }
     const nextActiveSurface = selectActiveRightPanelSurface(
       useRightPanelStore.getState().byThreadKey,
diff --git a/apps/web/src/rightPanelStore.test.ts b/apps/web/src/rightPanelStore.test.ts
index a29cecac37095..764fad8879bc4 100644
--- a/apps/web/src/rightPanelStore.test.ts
+++ b/apps/web/src/rightPanelStore.test.ts
@@ -1181,6 +1181,24 @@ describe("rightPanelStore", () => {
     });
   });
 
+  it("hides the panel when browser reconciliation removes its last session tab", () => {
+    const store = useRightPanelStore.getState();
+    store.openBrowser(refA, "tab-a");
+    store.reconcileBrowserSurfaces(refA, []);
+    expect(selectThreadRightPanelState(useRightPanelStore.getState().byThreadKey, refA)).toEqual({
+      isOpen: false,
+      activeSurfaceId: null,
+      surfaces: [],
+    });
+
+    store.openBrowser(refA, "tab-b");
+    store.open(refA, "diff");
+    store.reconcileBrowserSurfaces(refA, []);
+    expect(
+      selectThreadRightPanelState(useRightPanelStore.getState().byThreadKey, refA),
+    ).toMatchObject({ isOpen: true, activeSurfaceId: "diff" });
+  });
+
   it("moves a surface to a new index and keeps it there through browser reconciliation", () => {
     const store = useRightPanelStore.getState();
     store.openTerminal(refA, "term-1");
diff --git a/apps/web/src/rightPanelStore.ts b/apps/web/src/rightPanelStore.ts
index 5d4d68264aebd..33c537a3cf942 100644
--- a/apps/web/src/rightPanelStore.ts
+++ b/apps/web/src/rightPanelStore.ts
@@ -972,8 +972,14 @@ export const useRightPanelStore = create<RightPanelStoreState>()(
               (surface) => surface.id === current.activeSurfaceId,
             );
             const fallbackBrowser = surfaces.find((surface) => surface.kind === "preview");
+            // A closed session tab was the last surface: hide the panel rather than leave it on
+            // the empty picker, as a user close would. A dropped `browser:new` placeholder does not count.
+            const closedLastSessionTab =
+              surfaces.length === 0 &&
+              current.surfaces.some((surface) => surface.kind === "preview" && surface.resourceId);
             return {
               ...current,
+              isOpen: closedLastSessionTab ? false : current.isOpen,
               surfaces,
               activeSurfaceId: activeStillExists
                 ? current.activeSurfaceId