diff --git a/packages/views/chat/components/use-chat-resize.ts b/packages/views/chat/components/use-chat-resize.ts
index a5f17622e..01a53ddeb 100644
--- a/packages/views/chat/components/use-chat-resize.ts
+++ b/packages/views/chat/components/use-chat-resize.ts
@@ -34,11 +34,16 @@ export function useChatResize(
     if (!parent) return;
 
     const update = () => {
-      boundsRef.current = {
-        maxW: Math.floor(parent.clientWidth * MAX_RATIO),
-        maxH: Math.floor(parent.clientHeight * MAX_RATIO),
-      };
-      setBoundsReady(true);
+      const maxW = Math.floor(parent.clientWidth * MAX_RATIO);
+      const maxH = Math.floor(parent.clientHeight * MAX_RATIO);
+      setBoundsReady(true); // idempotent once true
+      // Only trigger a re-render if the bounds actually changed. Without this
+      // guard, any spurious ResizeObserver notification (including sub-pixel
+      // layout jitter during mount) schedules a setState that feeds back into
+      // the observer, producing "Maximum update depth exceeded".
+      const prev = boundsRef.current;
+      if (prev.maxW === maxW && prev.maxH === maxH) return;
+      boundsRef.current = { maxW, maxH };
       setRevision((r) => r + 1);
     };
 
diff --git a/packages/views/layout/app-sidebar.tsx b/packages/views/layout/app-sidebar.tsx
index a24766030..16fc90b04 100644
--- a/packages/views/layout/app-sidebar.tsx
+++ b/packages/views/layout/app-sidebar.tsx
@@ -78,6 +78,16 @@ import { useDeletePin, useReorderPins } from "@multica/core/pins/mutations";
 import type { PinnedItem } from "@multica/core/types";
 import { useLogout } from "../auth";
 
+// Stable empty arrays for query defaults. Using an inline `= []` default on
+// `useQuery` creates a new array reference on every render when `data` is
+// undefined (e.g. query disabled or loading) — which in turn breaks any
+// `useEffect`/`useMemo` that depends on the value, and can trigger infinite
+// re-render loops when the effect itself calls `setState`.
+const EMPTY_PINS: PinnedItem[] = [];
+const EMPTY_WORKSPACES: Awaited<ReturnType<typeof api.listWorkspaces>> = [];
+const EMPTY_INVITATIONS: Awaited<ReturnType<typeof api.listMyInvitations>> = [];
+const EMPTY_INBOX: Awaited<ReturnType<typeof api.listInbox>> = [];
+
 // Nav items reference WorkspacePaths method names so they can be resolved
 // against the current workspace slug at render time (see AppSidebar body).
 // Only parameterless paths are valid nav destinations.
@@ -202,11 +212,11 @@ export function AppSidebar({ topSlot, searchSlot, headerClassName, headerStyle }
   const logout = useLogout();
   const workspace = useCurrentWorkspace();
   const p = useWorkspacePaths();
-  const { data: workspaces = [] } = useQuery(workspaceListOptions());
-  const { data: myInvitations = [] } = useQuery(myInvitationListOptions());
+  const { data: workspaces = EMPTY_WORKSPACES } = useQuery(workspaceListOptions());
+  const { data: myInvitations = EMPTY_INVITATIONS } = useQuery(myInvitationListOptions());
 
   const wsId = workspace?.id;
-  const { data: inboxItems = [] } = useQuery({
+  const { data: inboxItems = EMPTY_INBOX } = useQuery({
     queryKey: wsId ? inboxKeys.list(wsId) : ["inbox", "disabled"],
     queryFn: () => api.listInbox(),
     enabled: !!wsId,
@@ -216,7 +226,7 @@ export function AppSidebar({ topSlot, searchSlot, headerClassName, headerStyle }
     [inboxItems],
   );
   const hasRuntimeUpdates = useMyRuntimesNeedUpdate(wsId);
-  const { data: pinnedItems = [] } = useQuery({
+  const { data: pinnedItems = EMPTY_PINS } = useQuery({
     ...pinListOptions(wsId ?? "", userId ?? ""),
     enabled: !!wsId && !!userId,
   });