fix: bootstrap embedded chat prompting state and review read-only handling

Pass initial subagent prompting settings into embedded chat URLs and views
Prevent inactive embedded chats from stealing focus on load
Treat review sessions as independent conversations when resolving prompt read-only state

packages/ui/src/components/layout/contextPanelEmbeddedChat.test.ts

@@ -128,6 +128,17 @@ describe('embedded session chat URL', () => {
     expect(new URL(second).searchParams.get('themeVariant')).toBe('dark');
   });
 
+  test('bootstraps subagent prompting before the embedded chat first renders', () => {
+    const src = buildEmbeddedSessionChatURL('ses_1', '/repo', false, {
+      mode: 'system',
+      lightThemeId: 'light-a',
+      darkThemeId: 'dark-a',
+      currentTheme: makeTheme('dark-a', 'dark'),
+    }, { allowPromptingSubagentSessions: true });
+
+    expect(new URL(src).searchParams.get('allowPromptingSubagentSessions')).toBe('1');
+  });
+
   test('rebuilds cached src when readOnly changes for an existing tab', () => {
     const cache = new Map<string, EmbeddedSessionChatURLCacheEntry>();
     const theme = {