wip: pane/session + tab-bar checkpoint

Second checkpoint of in-flight work (sessions route, api types, ChatTabBar,
PaneHeaderActions, Workspace, useWorkspacePanes) so the Orchestrator branch
can rebase onto current main before merge.

apps/web/src/api/types.ts

@@ -392,6 +392,11 @@ export type WorkspacePaneKind =
   | 'markdown_artifact'
   | 'html_artifact';
 
+// Mixed tabs: a pane can hold tabs of different kinds (a BooChat tab next to a
+// BooCode tab next to a Terminal tab). Each tab carries its own kind; the active
+// tab's kind drives what the pane renders. `tabKinds` is parallel to `chatIds`.
+export type WorkspaceTabKind = 'chat' | 'coder' | 'terminal';
+
 // v1.14.x: per-pane artifact payloads. Optional + namespaced so older saved
 // pane rows (without these fields) deserialize unchanged.
 // v1.14.x: pane state is a reference only — the pane component fetches the
@@ -413,9 +418,17 @@ export interface HtmlArtifactState {
 
 export interface WorkspacePane {
   id: string;
+  // For a tabbed pane (chat/coder/terminal) this mirrors the ACTIVE tab's kind,
+  // so the existing render-by-pane.kind path renders the active tab. Special
+  // panes (empty/settings/artifact) keep their own kind.
   kind: WorkspacePaneKind;
   chatId?: string;
+  // Tab ids. For chat/coder tabs this is the chats-row id; for terminal tabs
+  // it's a generated id used to key the tmux session. Parallel to tabKinds.
   chatIds: string[];
+  // Per-tab kind, parallel to chatIds. Optional for legacy rows (back-filled on
+  // load from pane.kind via normalizePaneKind).
+  tabKinds?: WorkspaceTabKind[];
   activeChatIdx: number;
   // v1.14.x: populated only when kind === 'markdown_artifact' / 'html_artifact'.
   markdown_artifact_state?: MarkdownArtifactState;
@@ -428,6 +441,7 @@ export interface WorkspacePane {
 export interface ClosedPaneEntry {
   kind: WorkspacePane['kind'];
   chatIds: string[];
+  tabKinds?: WorkspaceTabKind[];
   activeChatIdx: number;
 }