fix(frontend): isolate sidebar registration to unblock navigation

Separate shell subscriptions from Home session data and cover effect convergence, transition cleanup, current callbacks and signed-out fallback with real React lifecycle tests. Record baseline-equivalent local failures and outstanding browser/build verification.

Co-Authored-By: Claude Code <noreply@anthropic.com>

frontend/src/app/(app)/layout.tsx

@@ -4,13 +4,13 @@ import type { ReactNode } from "react";
 
 import { AppSidebar } from "@/components/app-sidebar";
 import { SidebarInset, SidebarProvider } from "@/components/ui/sidebar";
-import { SessionListProvider, sessionListSidebarModel, useSessionList } from "@/hooks/use-session-list";
+import { SessionListProvider, sessionListSidebarModel, useSessionList, useShellRegistration } from "@/hooks/use-session-list";
 import "../site-styles";
 
 function AppShell({ children }: { children: ReactNode }) {
   const list = useSessionList();
-  const { sessions, account } = sessionListSidebarModel(list);
-  const registration = list.registration;
+  const registration = useShellRegistration();
+  const { sessions, account } = sessionListSidebarModel(list, registration);
 
   return (
     <SidebarProvider escapeBlocked={registration?.escapeBlocked ?? false}>

frontend/src/hooks/use-session-list.ts

@@ -1 +1 @@
-export { SessionListProvider, useSessionList, sessionListSidebarModel } from "@/lib/session-list-context";
+export { SessionListProvider, useSessionList, useShellRegistration, sessionListSidebarModel } from "@/lib/session-list-context";

frontend/src/lib/session-list-context.tsx

@@ -55,10 +55,13 @@ export type SessionListContextValue = {
   ready: Promise<void>;
   boot: () => SessionListBoot | null;
   registerShellControls: (registration: ShellRegistration | null) => void;
-  registration: ShellRegistration | null;
 };
 
 const SessionListContext = createContext<SessionListContextValue | null>(null);
+// Home produces these controls; only the shell subscribes to their updates.
+// Publishing them through the data context re-renders Home, whose registration
+// effect has fresh callbacks/rows, feeding another update back to the provider.
+const ShellRegistrationContext = createContext<ShellRegistration | null>(null);
 
 function createReadyGate(): { promise: Promise<void>; resolve: () => void } {
   let settle = () => {};
@@ -167,20 +170,24 @@ export function SessionListProvider({ children }: { children: ReactNode }) {
     ready: readyPack.promise,
     boot,
     registerShellControls,
-    registration,
   }), [
     account,
     boot,
     readyPack.promise,
     registerShellControls,
-    registration,
     sessions,
     sessionsCursor,
     settled,
     signedOut,
   ]);
 
-  return <SessionListContext.Provider value={value}>{children}</SessionListContext.Provider>;
+  return (
+    <SessionListContext.Provider value={value}>
+      <ShellRegistrationContext.Provider value={registration}>
+        {children}
+      </ShellRegistrationContext.Provider>
+    </SessionListContext.Provider>
+  );
 }
 
 export function useSessionList(): SessionListContextValue {
@@ -191,11 +198,17 @@ export function useSessionList(): SessionListContextValue {
   return value;
 }
 
-export function sessionListSidebarModel(list: SessionListContextValue): {
+export function useShellRegistration(): ShellRegistration | null {
+  return useContext(ShellRegistrationContext);
+}
+
+export function sessionListSidebarModel(
+  list: SessionListContextValue,
+  registered: ShellRegistration | null,
+): {
   sessions: readonly SidebarSession[];
   account: SidebarAccount | null;
 } {
-  const registered = list.registration;
   return {
     sessions: registered?.sidebarSessions ?? sessionsToSidebarRows(list.sessions),
     account: registered?.sidebarAccount ?? toSidebarAccount(list.account),