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.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/routes/sessions.ts

@@ -40,11 +40,15 @@ const PaneKindZ = z.enum([
   'html_artifact',
 ]);
 
+// Mixed tabs: each tab carries its own kind (parallel to chatIds).
+const TabKindZ = z.enum(['chat', 'coder', 'terminal']);
+
 const WorkspacePaneZ = z.object({
   id: z.string().min(1).max(200),
   kind: PaneKindZ,
   chatId: z.string().min(1).max(200).optional(),
   chatIds: z.array(z.string().min(1).max(200)).max(50),
+  tabKinds: z.array(TabKindZ).max(50).optional(),
   activeChatIdx: z.number().int(),
   markdown_artifact_state: MarkdownArtifactStateZ.optional(),
   html_artifact_state: HtmlArtifactStateZ.optional(),
@@ -57,6 +61,7 @@ const WorkspacePaneZ = z.object({
 const ClosedPaneEntryZ = z.object({
   kind: PaneKindZ,
   chatIds: z.array(z.string().min(1).max(200)).max(50),
+  tabKinds: z.array(TabKindZ).max(50).optional(),
   activeChatIdx: z.number().int(),
 });