diff --git a/apps/server/src/routes/sidebar.ts b/apps/server/src/routes/sidebar.ts
index 4b543db..be79948 100644
--- a/apps/server/src/routes/sidebar.ts
+++ b/apps/server/src/routes/sidebar.ts
@@ -18,7 +18,7 @@ export function registerSidebarRoutes(app: FastifyInstance, sql: Sql): void {
       projects.map(async (p) => {
         const [recent_sessions, countRows] = await Promise.all([
           sql<SidebarSession[]>`
-            SELECT id, name, model, updated_at
+            SELECT id, project_id, name, model, updated_at
             FROM sessions
             WHERE project_id = ${p.id}
             ORDER BY updated_at DESC
diff --git a/apps/server/src/schema.sql b/apps/server/src/schema.sql
index ee0fc89..66ca449 100644
--- a/apps/server/src/schema.sql
+++ b/apps/server/src/schema.sql
@@ -46,3 +46,14 @@ CREATE TABLE IF NOT EXISTS settings (
 );
 
 INSERT INTO settings (key, value) VALUES ('default_model', '"qwen3.6-35b-a3b-mxfp4"') ON CONFLICT (key) DO NOTHING;
+
+CREATE TABLE IF NOT EXISTS session_panes (
+  id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  session_id   UUID NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
+  position     INTEGER NOT NULL,
+  kind         TEXT NOT NULL CHECK (kind IN ('chat', 'file_browser')),
+  state        JSONB NOT NULL DEFAULT '{}',
+  created_at   TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp(),
+  UNIQUE (session_id, position)
+);
+CREATE INDEX IF NOT EXISTS session_panes_session_idx ON session_panes (session_id);
diff --git a/apps/server/src/types/api.ts b/apps/server/src/types/api.ts
index 3413f58..73068db 100644
--- a/apps/server/src/types/api.ts
+++ b/apps/server/src/types/api.ts
@@ -61,6 +61,7 @@ export interface ModelInfo {
 
 export interface SidebarSession {
   id: string;
+  project_id: string;
   name: string;
   model: string;
   updated_at: string;
@@ -76,3 +77,68 @@ export interface SidebarProject {
 export interface SidebarResponse {
   projects: SidebarProject[];
 }
+
+export type PaneKind = 'chat' | 'file_browser';
+
+export interface FileBrowserPaneState {
+  open_file?: string | null;
+  filter?: string;
+  expanded_dirs?: string[];
+}
+
+// chat panes have no state for now
+export type ChatPaneState = Record<string, never>;
+
+export type PaneState = ChatPaneState | FileBrowserPaneState;
+
+export interface Pane {
+  id: string;
+  session_id: string;
+  position: number;
+  kind: PaneKind;
+  state: PaneState;
+  created_at: string;
+}
+
+export interface PaneCreateRequest {
+  kind: PaneKind;
+  position?: number;  // optional; if omitted, append at end
+}
+
+export interface PaneUpdateRequest {
+  state?: PaneState;
+  position?: number;
+}
+
+// User-stream frames (broadcast on /ws/user channel)
+export interface ProjectCreatedFrame {
+  type: 'project_created';
+  project: Project;
+}
+export interface ProjectDeletedFrame {
+  type: 'project_deleted';
+  project_id: string;
+}
+export interface SessionCreatedFrame {
+  type: 'session_created';
+  session: Session;
+  project_id: string;
+}
+export interface SessionDeletedFrame {
+  type: 'session_deleted';
+  session_id: string;
+  project_id: string;
+}
+export interface SessionUpdatedFrame {
+  type: 'session_updated';
+  session_id: string;
+  project_id: string;
+  name: string;
+  updated_at: string;
+}
+export type UserStreamFrame =
+  | ProjectCreatedFrame
+  | ProjectDeletedFrame
+  | SessionCreatedFrame
+  | SessionDeletedFrame
+  | SessionUpdatedFrame;