Keep forked chats focused in new tabs (#2038)

* fix(app): focus explicitly opened workspace tabs

Explicit tab navigation could be overwritten by attention-aware workspace
navigation when the visible agent had just finished. Make workspace navigation
own both normal attention selection and explicit targets so callers cannot
sequence them inconsistently.

* test(app): strengthen forked tab focus assertion

packages/app/src/utils/workspace-navigation.ts

@@ -1,16 +1,10 @@
-import { navigateToWorkspace } from "@/stores/navigation-active-workspace-store";
 import { useWorkspaceLayoutStore } from "@/stores/workspace-layout-store";
 import {
   prepareWorkspaceTab as prepareWorkspaceTabPure,
-  navigateToPreparedWorkspaceTab as navigateToPreparedWorkspaceTabPure,
   type PrepareWorkspaceTabInput,
-  type NavigateToPreparedWorkspaceTabInput,
 } from "./prepare-workspace-tab";
 
-export type {
-  PrepareWorkspaceTabInput,
-  NavigateToPreparedWorkspaceTabInput,
-} from "./prepare-workspace-tab";
+export type { PrepareWorkspaceTabInput } from "./prepare-workspace-tab";
 
 function layoutStoreDeps() {
   const store = useWorkspaceLayoutStore.getState();
@@ -20,13 +14,6 @@ function layoutStoreDeps() {
   };
 }
 
-export function prepareWorkspaceTab(input: PrepareWorkspaceTabInput): string {
-  return prepareWorkspaceTabPure(input, layoutStoreDeps());
-}
-
-export function navigateToPreparedWorkspaceTab(input: NavigateToPreparedWorkspaceTabInput): string {
-  return navigateToPreparedWorkspaceTabPure(input, {
-    ...layoutStoreDeps(),
-    navigateToWorkspace,
-  });
+export function prepareWorkspaceTab(input: PrepareWorkspaceTabInput): void {
+  prepareWorkspaceTabPure(input, layoutStoreDeps());
 }