fix: home's acting-on pick switches the current workspace (#11929)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/components/sessions/HomeSessionStarter.svelte

@@ -83,7 +83,7 @@
 
 {#snippet actingOn()}
 	{#if session}
-		<SessionWorkspaceBar {session} />
+		<SessionWorkspaceBar {session} switchesWorkspace />
 	{/if}
 {/snippet}
 

frontend/src/lib/components/sessions/SessionWorkspaceBar.svelte

@@ -8,8 +8,22 @@
 	} from './sessionState.svelte'
 	import WorkspaceFamilyPicker from './WorkspaceFamilyPicker.svelte'
 	import WorkspaceScopeTrigger from '$lib/components/WorkspaceScopeTrigger.svelte'
+	import { switchWorkspace } from '$lib/storeUtils'
+	import { workspaceAIClients } from '$lib/components/copilot/lib'
+	import { fixupUrlAfterWorkspaceSwitch } from '$lib/components/sidebar/workspaceSwitchUrl'
 
-	let { session }: { session: Session } = $props()
+	// `switchesWorkspace`: a pick also moves the navigation workspace. For a host whose page
+	// shows the navigation workspace around the composer (Home), where a pick that left it
+	// behind would read as ignored; the session page follows the session's own workspace instead.
+	let { session, switchesWorkspace = false }: { session: Session; switchesWorkspace?: boolean } =
+		$props()
+
+	function followPick(id: string) {
+		if (!switchesWorkspace || $workspaceStore === id) return
+		workspaceAIClients.init(id)
+		switchWorkspace(id)
+		void fixupUrlAfterWorkspaceSwitch(id)
+	}
 
 	// Effective workspace for display: committed → pending pick → active store.
 	const effectiveId = $derived(getEffectiveWorkspaceId(session) ?? $workspaceStore ?? undefined)
@@ -17,14 +31,15 @@
 
 	function pick(id: string) {
 		// Pre-send only: writes the pending pick. workspace_id stays undefined until
-		// the user sends their first message. The global workspaceStore is left
-		// untouched — the chat targets this pending workspace via the manager's
-		// workspace resolver, so picking here must not switch the active workspace.
+		// the user sends their first message. The chat targets this pending workspace
+		// via the manager's workspace resolver, not the global workspaceStore.
 		setSessionPendingWorkspace(session.id, id)
+		followPick(id)
 	}
 
 	function stageFork(req: { parent_workspace_id: string; id: string; name: string }) {
 		setSessionPendingFork(session.id, req)
+		followPick(req.parent_workspace_id)
 	}
 </script>