feat: implement new session behavior to clear selection and show empty state

- Added bilingual notes for the new session feature, detailing the transition to an empty state upon session creation.
- Updated `SessionsService` to include a `clear()` method that resets the current selection and persists the empty state.
- Enhanced the `EmptyState` component to reflect the new design, including workspace selection and input handling.
- Modified CSS styles for improved layout and visual consistency in the empty state.
- Updated tests to cover the new session clearing functionality and its effects on the UI.

packages/client/ui-sidebar/README.md

@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-client-ui-sidebar
 
-Sidebar plugin: session multi-level tree (cwd grouping + parentId nesting), search, by-workspace grouping, state dots, three creation entries. Collapse is a slide + crossfade into the layout-owned 56px rail (open / new session / new workspace / search — search expands and focuses the search box — plus the settings foot): the expanded content freezes at its width and fades in place while the column slides over it, then the rail — whale mark resting, panel icon on hover, tooltips on every control — crossfades in at settle as the wide content unmounts. Contract: the [slot system standard](../../../.agents/notes/implemented/architecture/2026-07-22-slot-type-chain-implementation.md).
+Sidebar plugin: session multi-level tree (cwd grouping + parentId nesting), search, by-workspace grouping, state dots, three creation entries. Top-level New Session / New Workspace clear the selection onto `conversation.empty`; per-project "+" still create-then-opens. Collapse is a slide + crossfade into the layout-owned 56px rail (open / new session / new workspace / search — search expands and focuses the search box — plus the settings foot): the expanded content freezes at its width and fades in place while the column slides over it, then the rail — whale mark resting, panel icon on hover, tooltips on every control — crossfades in at settle as the wide content unmounts. Contract: the [slot system standard](../../../.agents/notes/implemented/architecture/2026-07-22-slot-type-chain-implementation.md).
 
 `src/client/contract/slots.ts` is the single-domain contract file: `SidebarRootInjected` (the registrant's own injected share — plain service callbacks: onOpen/onCreate/onToggleSidebar) and `SidebarRootComponentProps = PropsRuntime<'sidebar'> & SidebarRootInjected` (owner `{collapsed,width}` plus the standard `useSessions` hook, resolved off ui-layout's SlotMap declaration, never re-stated). `apply` registers SidebarRoot cast-free against that composition; the inject factory closes over the plugin's own ctx.
 

packages/client/ui-sidebar/src/client/contract/slots.ts

@@ -25,8 +25,8 @@ export type SidebarRootInjected = {
   /** Open (switch to) a session. */
   onOpen: (id: SessionId) => void
   /**
-   * Create a session and open it; cwd targets a project group (the
-   * sidebar's three creation entries all land in the new session).
+   * New-session affordance: no cwd clears selection onto the empty-state
+   * launch; a cwd create-then-opens a session in that project group.
    */
   onCreate: (cwd?: string) => void
   /** Collapse the sidebar column (layout service action; owner share stays {collapsed,width}). */

packages/client/ui-sidebar/src/client/index.ts

@@ -27,9 +27,15 @@ export function apply(ctx: ClientContext): void {
     // list snapshot); layout keeps only panel geometry.
     onOpen: (id) => { ctx.sessions.open(id) },
     onCreate: (cwd) => {
-      // Create-then-open: the sidebar's three creation entries all land
-      // in the new session (empty-state first-send stays with ui-conversation).
-      void ctx.sessions.create(cwd === undefined ? {} : { cwd })
+      // Top-level New Session / New Workspace: clear selection so AppFrame
+      // shows conversation.empty (EmptyState + shared InputBar). Per-project
+      // "+" still create-then-opens into that cwd until workspace seeding
+      // reaches the empty-state picker.
+      if (cwd === undefined) {
+        ctx.sessions.clear()
+        return
+      }
+      void ctx.sessions.create({ cwd })
         .then((id: SessionId) => { ctx.sessions.open(id) })
     },
     onToggleSidebar: () => { ctx.layout.toggleSidebar() },

packages/client/ui-sidebar/tests/apply.spec.tsx

@@ -26,7 +26,12 @@ async function bench() {
     byId: { [sid('a')]: { id: sid('a'), title: 'alpha', displayTitle: 'alpha', cwd: '/proj', running: false, updatedAt: 1 } },
     current: undefined,
   })
-  const sessions = { list, create: vi.fn(async () => sid('minted')), open: vi.fn() }
+  const sessions = {
+    list,
+    create: vi.fn(async () => sid('minted')),
+    open: vi.fn(),
+    clear: vi.fn(),
+  }
   const layout = { toggleSidebar: vi.fn() }
   ctx.provide('sessions', sessions)
   ctx.provide('layout', layout)
@@ -91,14 +96,15 @@ describe('apply', () => {
     expect(sessions.open).toHaveBeenCalledWith('a')
 
     injected.onCreate()
-    expect(sessions.create).toHaveBeenCalledWith({})
+    expect(sessions.clear).toHaveBeenCalledOnce()
+    expect(sessions.create).not.toHaveBeenCalled()
+
+    injected.onCreate('/proj')
+    expect(sessions.create).toHaveBeenCalledWith({ cwd: '/proj' })
     // create-then-open lands after the create promise resolves.
     await Promise.resolve()
     await Promise.resolve()
     expect(sessions.open).toHaveBeenCalledWith('minted')
-
-    injected.onCreate('/proj')
-    expect(sessions.create).toHaveBeenCalledWith({ cwd: '/proj' })
   })
 
   it('teardown unregisters the slot entry', async () => {