fix(web): recalculate dockview layout after fast-path session switch (#571)

* fix(web): recalculate dockview layout after fast-path session switch

The fast path in tryFastSessionSwitch removed ephemeral panels but
never called api.layout() to redistribute column widths, leaving a
gap on the right side of the screen. Both slow-path branches already
make this call.

* test(web): add regression test for fast-path layout call

Verifies that performSessionSwitch calls api.layout() on both the
fast path and slow path, preventing the squished-layout regression.

* test(web): cover saved-layout fast path branch

* fix(web): replace no-explicit-any cast in test

* fix(web): fix test isolation with mockReturnValueOnce

Use mockReturnValueOnce and clearAllMocks for proper test isolation
between fast-path and slow-path test cases.

* test(web): fix mock shape to match LayoutGroupIds type

apps/web/lib/state/dockview-session-switch.test.ts

@@ -0,0 +1,84 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { performSessionSwitch, type SessionSwitchParams } from "./dockview-session-switch";
+
+// Mock dependencies
+vi.mock("@/lib/local-storage", () => ({
+  getSessionLayout: vi.fn(() => null),
+}));
+
+vi.mock("./dockview-layout-builders", () => ({
+  applyLayoutFixups: vi.fn(() => ({
+    sidebarGroupId: "g1",
+    centerGroupId: "g2",
+    rightTopGroupId: "g3",
+    rightBottomGroupId: "g4",
+  })),
+}));
+
+vi.mock("./layout-manager", () => ({
+  fromDockviewApi: vi.fn(() => ({ columns: [] })),
+  savedLayoutMatchesLive: vi.fn(() => false),
+  layoutStructuresMatch: vi.fn(() => false),
+}));
+
+import { getSessionLayout } from "@/lib/local-storage";
+import { layoutStructuresMatch, savedLayoutMatchesLive } from "./layout-manager";
+
+function makeMockApi() {
+  return {
+    panels: [],
+    layout: vi.fn(),
+    fromJSON: vi.fn(),
+    getPanel: vi.fn(),
+  } as unknown as SessionSwitchParams["api"];
+}
+
+function makeParams(overrides?: Partial<SessionSwitchParams>): SessionSwitchParams {
+  return {
+    api: makeMockApi(),
+    oldSessionId: "old-session",
+    newSessionId: "new-session",
+    safeWidth: 800,
+    safeHeight: 600,
+    buildDefault: vi.fn(),
+    getDefaultLayout: vi.fn(() => ({ columns: [] })),
+    ...overrides,
+  };
+}
+
+describe("performSessionSwitch", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("calls api.layout on the fast path when structures match", () => {
+    vi.mocked(layoutStructuresMatch).mockReturnValueOnce(true);
+    const params = makeParams();
+
+    performSessionSwitch(params);
+
+    expect(params.api.layout).toHaveBeenCalledWith(800, 600);
+  });
+
+  it("calls api.layout on the fast path when saved layout matches", () => {
+    vi.mocked(getSessionLayout).mockReturnValueOnce({ grid: {} } as unknown as ReturnType<
+      typeof getSessionLayout
+    >);
+    vi.mocked(savedLayoutMatchesLive).mockReturnValueOnce(true);
+    const params = makeParams();
+
+    performSessionSwitch(params);
+
+    expect(params.api.layout).toHaveBeenCalledWith(800, 600);
+    expect(params.api.fromJSON).not.toHaveBeenCalled();
+  });
+
+  it("calls api.layout on the slow path (buildDefault fallback)", () => {
+    const params = makeParams();
+
+    performSessionSwitch(params);
+
+    expect(params.api.layout).toHaveBeenCalledWith(800, 600);
+    expect(params.buildDefault).toHaveBeenCalledWith(params.api);
+  });
+});

apps/web/lib/state/dockview-session-switch.ts

@@ -83,6 +83,7 @@ function tryFastSessionSwitch(params: SessionSwitchParams): LayoutGroupIds | nul
   // Session-scoped portals (terminal, browser, etc.) will be re-acquired
   // via usePortalSlot's sessionId dependency change.
   removeEphemeralPanels(api, newSessionId);
+  api.layout(params.safeWidth, params.safeHeight);
   return applyLayoutFixups(api);
 }