fix(sidebar): preserve pinned sessions and folder refs on empty session list (#1706)

Added sessions.length === 0 guard to useSidebarPersistence.ts and
sessions.length === 0 && archivedSessions.length === 0 guard to
useSessionFolderCleanup.ts. Prevents data loss when server returns
empty list during transient failures.

Co-authored-by: Leonid Skorobogatyy <bash@opencode.itc.local>

packages/ui/src/components/session/sidebar/hooks/useSessionFolderCleanup.ts

@@ -38,6 +38,10 @@ export const useSessionFolderCleanup = (args: Args): void => {
       return;
     }
 
+    if (sessions.length === 0 && archivedSessions.length === 0) {
+      return;
+    }
+
     const idsByScope = new Map<string, Set<string>>();
     sessions.forEach((session) => {
       const directory = normalizePath((session as Session & { directory?: string | null }).directory ?? null);

packages/ui/src/components/session/sidebar/hooks/useSidebarPersistence.ts

@@ -154,6 +154,10 @@ export const useSidebarPersistence = (args: Args) => {
       return;
     }
 
+    if (sessions.length === 0) {
+      return;
+    }
+
     const existingSessionIds = new Set(sessions.map((session) => session.id));
     setPinnedSessionIds((prev) => {
       let changed = false;