fix(app): keep Cmd+T working after switching workspaces

The new-tab menu handler registered itself as
`workspace-new-tab-menu:<serverId>:<paneId>`, leaving out the workspace.
Pane ids are namespaced per workspace — every workspace's default pane is
called "main" — so all workspaces on a host produced the same handler id.

The deck keeps several workspaces mounted at once, the dispatcher stores
one live handler per id, and useKeyboardActionHandler registers once per
id and never re-registers on focus change. So the second workspace to
mount evicted the first, and switching back left a mounted, focused
workspace with no handler at all: Cmd+T and Cmd+Shift+A/T/C/E silently
did nothing until the newer entry expired from the deck.

Handler ids are now built from the surface's full identity rather than
assembled at the call site, so the workspace can't be dropped again. The
three workspace-wide handlers move onto the same constructor; they were
already correct, but the shape belongs in one place.

packages/app/src/screens/workspace/workspace-desktop-tabs-row.tsx

@@ -104,6 +104,7 @@ import { useWorkspaceDirectory } from "@/stores/session-store-hooks";
 import { useCheckoutStatusQuery } from "@/git/use-status-query";
 import { TrailingActionScrim } from "@/components/ui/trailing-action-scrim";
 import { useKeyboardActionHandler } from "@/hooks/use-keyboard-action-handler";
+import { buildWorkspaceKeyboardHandlerId } from "@/keyboard/handler-id";
 import type { KeyboardActionDefinition } from "@/keyboard/keyboard-action-dispatcher";
 
 const DROPDOWN_WIDTH = 220;
@@ -1489,7 +1490,12 @@ function ResolvedWorkspaceDesktopTabsRow({
   );
 
   useKeyboardActionHandler({
-    handlerId: `workspace-new-tab-menu:${normalizedServerId}:${paneId ?? "main"}`,
+    handlerId: buildWorkspaceKeyboardHandlerId({
+      name: "workspace-new-tab-menu",
+      serverId: normalizedServerId,
+      workspaceId: normalizedWorkspaceId,
+      paneId,
+    }),
     actions: [
       "workspace.tab.menu.open",
       "workspace.tab.target.agent",

packages/app/src/screens/workspace/workspace-screen.tsx

@@ -67,6 +67,7 @@ import {
   type WorkspaceTabTarget,
 } from "@/workspace-tabs/model";
 import { useKeyboardActionHandler } from "@/hooks/use-keyboard-action-handler";
+import { buildWorkspaceKeyboardHandlerId } from "@/keyboard/handler-id";
 import type { KeyboardActionDefinition } from "@/keyboard/keyboard-action-dispatcher";
 import { useCreateFlowStore } from "@/stores/create-flow-store";
 import {
@@ -3042,7 +3043,11 @@ function WorkspaceScreenContent({
   );
 
   useKeyboardActionHandler({
-    handlerId: `workspace-tab-actions:${normalizedServerId}:${normalizedWorkspaceId}`,
+    handlerId: buildWorkspaceKeyboardHandlerId({
+      name: "workspace-tab-actions",
+      serverId: normalizedServerId,
+      workspaceId: normalizedWorkspaceId,
+    }),
     actions: [
       "workspace.agent.new",
       "workspace.tab.close-current",
@@ -3058,7 +3063,11 @@ function WorkspaceScreenContent({
   });
 
   useKeyboardActionHandler({
-    handlerId: `workspace-pane-actions:${normalizedServerId}:${normalizedWorkspaceId}`,
+    handlerId: buildWorkspaceKeyboardHandlerId({
+      name: "workspace-pane-actions",
+      serverId: normalizedServerId,
+      workspaceId: normalizedWorkspaceId,
+    }),
     actions: [
       "workspace.pane.split.right",
       "workspace.pane.split.down",
@@ -3080,7 +3089,11 @@ function WorkspaceScreenContent({
   });
 
   useKeyboardActionHandler({
-    handlerId: `workspace-sidebar-actions:${normalizedServerId}:${normalizedWorkspaceId}`,
+    handlerId: buildWorkspaceKeyboardHandlerId({
+      name: "workspace-sidebar-actions",
+      serverId: normalizedServerId,
+      workspaceId: normalizedWorkspaceId,
+    }),
     actions: ["sidebar.toggle.right"] as const,
     enabled: Boolean(isRouteFocused && normalizedServerId && normalizedWorkspaceId),
     priority: 100,