fix(ui): collapse chat side panel after final tab closes (#130102)

* fix(ui): collapse side panel after final tab closes

* fix(ui): preserve side panel owner state

* fix(ui): preserve projected panel closure

* fix(ui): align projected panel close contract

ui/src/e2e/chat-rail-columns.e2e.test.ts

@@ -815,8 +815,10 @@ suite.define(() => {
               .getByRole("button", { name: `Close ${label}`, exact: true })
               .click();
           }
-          await sidePanel(page).locator(".side-panel-empty--selector").waitFor();
-          await sidePanel(page).getByRole("button", { name: "Close", exact: true }).click();
+          await expect.poll(() => sidePanel(page).count()).toBe(0);
+          await page.reload();
+          await page.locator(".chat-group").first().waitFor();
+          await expect.poll(() => sidePanel(page).count()).toBe(0);
           await page.locator(".chat-side-panel-toggle").click();
           await sidePanel(page).locator(".side-panel-empty--selector").waitFor();
           expect(await sidePanel(page).locator("wa-tab").count()).toBe(0);

ui/src/e2e/chat-sidebar-panel-contract.e2e.test.ts

@@ -407,6 +407,9 @@ suite.define(() => {
       await waitForControlUiGatewayReady(page);
 
       const panel = page.locator(".sidebar-region__right-runtime .side-panel");
+      await expect.poll(() => panel.count()).toBe(0);
+
+      await page.locator(".chat-side-panel-toggle").click();
       await panel.locator(".side-panel-empty--selector").waitFor();
       expect(await panel.locator("wa-tab").count()).toBe(0);
 

ui/src/pages/chat/chat-pane-sidebar-layout.test.ts

@@ -197,6 +197,25 @@ describe("chat pane sidebar layout", () => {
     }
   });
 
+  it("closes an empty Board projection and preserves visibility with a real tab", () => {
+    for (const open of [true, false]) {
+      const empty = resolveSidebarLayoutForBoard({
+        board: board("hidden", "chat"),
+        layout: { ...openSlot({ columns: [] }, "chat"), open },
+        paneWidth: 1_400,
+      });
+      expect(empty).toMatchObject({ columns: [], open: false });
+
+      const withDetail = resolveSidebarLayoutForBoard({
+        board: board("hidden", "chat"),
+        layout: { ...openSlot(openSlot({ columns: [] }, "chat"), "detail"), open },
+        paneWidth: 1_400,
+      });
+      expect(withDetail.columns[0]?.panels.map((panel) => panel.slot)).toEqual(["detail"]);
+      expect(withDetail.open).toBe(open);
+    }
+  });
+
   it("keeps the detail tab when its transient content is no longer available", () => {
     const layout = resolveSidebarLayoutForBoard({
       board: board("hidden", "chat"),

ui/src/pages/chat/chat-pane.test.ts

@@ -922,7 +922,7 @@ describe("chat pane keyboard shortcuts", () => {
     expect(state.sidebarLayout.columns[0]?.panels.map((panel) => panel.slot)).toEqual(["terminal"]);
     expect(press().defaultPrevented).toBe(true);
     expect(state.sidebarLayout.columns).toEqual([]);
-    expect(state.sidebarLayout.open).toBe(true);
+    expect(state.sidebarLayout.open).toBe(false);
   });
 });
 

ui/src/pages/chat/sidebar-layout-types.ts

@@ -21,7 +21,6 @@ export type SidebarColumn = {
 export type SidebarLayout = {
   columns: SidebarColumn[];
   dock?: SidebarDock;
-  /** The panel may stay open as a type picker after its last tab closes. */
   open?: boolean;
   expanded?: boolean;
 };

ui/src/pages/chat/sidebar-layout.test.ts

@@ -71,9 +71,16 @@ describe("sidebar layout", () => {
     expect(chat?.slot).toBe("chat");
   });
 
-  it("keeps the panel open as a type selector after its final tab closes", () => {
+  it("collapses the panel after its final tab closes", () => {
     const closed = closeSlot(openSlot({ columns: [] }, "detail"), "detail");
-    expect(closed).toEqual({ columns: [], open: true });
+    expect(closed).toEqual({ columns: [], open: false });
+  });
+
+  it("does not reopen a minimized panel when another tab remains", () => {
+    const minimized = { ...openAll(), open: false };
+    const closed = closeSlot(minimized, "detail");
+    expect(closed.open).toBe(false);
+    expect(closed.columns[0]?.panels.map((panel) => panel.slot)).toEqual(["discussion", "chat"]);
   });
 
   it("minimizes and expands without discarding tabs", () => {

ui/src/pages/chat/sidebar-layout.ts

@@ -122,6 +122,9 @@ export function closeSlot(layout: SidebarLayout, slot: SidebarSlotId): SidebarLa
     .find((entry) => entry.slot === slot);
   if (panel) {
     removePanel(next, panel.id);
+    if (next.columns.length === 0) {
+      next.open = false;
+    }
   }
   return next;
 }