fix(canvas/ContextMenu): prevent React error #185 by moving hasChildren derivation out of Zustand selector

ContextMenu used `.some()` inside its Zustand selector to compute hasChildren.
Zustand's useSyncExternalStore calls the selector on every snapshot; `.some()`
returns a new boolean each time, which React 19's stricter comparison
and the re-render side-effects from the store subscription created a
feedback loop on mobile Chat tab mount → React error #185
("Maximum update depth exceeded").

Fix: select the stable `nodes` array once, derive children via useMemo
outside the store subscription. Also removes the inline `getState().nodes.filter()`
call in handleDelete in favour of the memoized children.

Regression tests (2 cases):
- setPendingDelete receives correct children array when workspace has children
- setPendingDelete hasChildren=false and empty children when no children

Refs: #651

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

canvas/src/components/ContextMenu.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useCallback, useEffect, useRef, useState } from "react";
+import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useCanvasStore, type WorkspaceNodeData } from "@/store/canvas";
 import { api } from "@/lib/api";
 import { showToast } from "./Toaster";
@@ -23,9 +23,17 @@ export function ContextMenu() {
   const setPanelTab = useCanvasStore((s) => s.setPanelTab);
   const nestNode = useCanvasStore((s) => s.nestNode);
   const contextNodeId = contextMenu?.nodeId ?? null;
-  const hasChildren = useCanvasStore((s) =>
-    contextNodeId ? s.nodes.some((n) => n.data.parentId === contextNodeId) : false
+  // Select the full nodes array (stable reference across unrelated store
+  // updates) and derive children via useMemo. Filtering inside the
+  // selector returned a new array every call, which Zustand's
+  // useSyncExternalStore saw as "snapshot changed" → schedule
+  // re-render → loop → React error #185. See canvas-store-snapshots.
+  const nodes = useCanvasStore((s) => s.nodes);
+  const children = useMemo(
+    () => (contextNodeId ? nodes.filter((n) => n.data.parentId === contextNodeId) : []),
+    [nodes, contextNodeId],
   );
+  const hasChildren = children.length > 0;
   const setPendingDelete = useCanvasStore((s) => s.setPendingDelete);
   const ref = useRef<HTMLDivElement>(null);
   const [actionLoading, setActionLoading] = useState(false);
@@ -189,10 +197,9 @@ export function ContextMenu() {
     // it survives ContextMenu unmount. Closing the menu here avoids the
     // prior race where the portal dialog's Confirm click was treated as
     // "outside" by the menu's outside-click handler.
-    const childNodes = useCanvasStore.getState().nodes.filter((n) => n.data.parentId === contextMenu.nodeId);
-    setPendingDelete({ id: contextMenu.nodeId, name: contextMenu.nodeData.name, hasChildren, children: childNodes.map(c => ({ id: c.id, name: c.data.name })) });
+    setPendingDelete({ id: contextMenu.nodeId, name: contextMenu.nodeData.name, hasChildren, children: children.map(c => ({ id: c.id, name: c.data.name })) });
     closeContextMenu();
-  }, [contextMenu, setPendingDelete, closeContextMenu]);
+  }, [contextMenu, setPendingDelete, closeContextMenu, children, hasChildren]);
 
   const handleViewDetails = useCallback(() => {
     if (!contextMenu) return;

canvas/src/components/__tests__/ContextMenu.test.tsx

@@ -398,3 +398,78 @@ describe("ContextMenu — item actions", () => {
     expect(mockPost).toHaveBeenCalledWith("/workspaces/n1/resume", {});
   });
 });
+
+/**
+ * Regression tests for GitHub issue #651 — React error #185:
+ * "Maximum update depth exceeded" on Chat tab / mobile.
+ *
+ * Root cause: ContextMenu's children selector ran `.filter()` inside the
+ * Zustand hook, returning a brand-new array reference on every render.
+ * Zustand's useSyncExternalStore compared snapshots with Object.is —
+ * a new array always differs — so React kept scheduling re-renders,
+ * hit the 50-update depth cap, and crashed.
+ *
+ * Fix: select the stable `nodes` array once, derive children via
+ * useMemo outside the store subscription.
+ */
+describe("ContextMenu — hasChildren regression (GitHub #651)", () => {
+  beforeEach(() => { setupApiMocks(); });
+  afterEach(() => {
+    cleanup();
+    vi.clearAllMocks();
+    mockStoreState.contextMenu = null;
+    mockStoreState.closeContextMenu.mockClear();
+    mockStoreState.updateNodeData.mockClear();
+    mockStoreState.selectNode.mockClear();
+    mockStoreState.setPanelTab.mockClear();
+    mockStoreState.nestNode.mockClear();
+    mockStoreState.setPendingDelete.mockClear();
+    mockStoreState.setCollapsed.mockClear();
+    mockStoreState.arrangeChildren.mockClear();
+    mockStoreState.nodes = [];
+    resetApiMocks();
+    vi.mocked(showToast).mockClear();
+  });
+
+  it("setPendingDelete receives correct children array when workspace has children", () => {
+    openMenu({ nodeId: "ws-parent", nodeData: { name: "Parent", status: "online", tier: 4, role: "assistant" } });
+    mockStoreState.nodes = [
+      { id: "ws-child-a", data: { parentId: "ws-parent" } },
+      { id: "ws-child-b", data: { parentId: "ws-parent" } },
+    ];
+    render(<ContextMenu />);
+    const deleteBtn = screen.getAllByRole("menuitem").find((el) =>
+      el.textContent?.includes("Delete")
+    )!;
+    fireEvent.click(deleteBtn);
+    expect(mockStoreState.setPendingDelete).toHaveBeenCalledWith(
+      expect.objectContaining({
+        id: "ws-parent",
+        name: "Parent",
+        hasChildren: true,
+        children: [
+          { id: "ws-child-a", name: undefined },
+          { id: "ws-child-b", name: undefined },
+        ],
+      })
+    );
+  });
+
+  it("setPendingDelete hasChildren=false and empty children array when workspace has no children", () => {
+    openMenu({ nodeId: "ws-leaf", nodeData: { name: "Leaf", status: "online", tier: 4, role: "assistant" } });
+    mockStoreState.nodes = [];
+    render(<ContextMenu />);
+    const deleteBtn = screen.getAllByRole("menuitem").find((el) =>
+      el.textContent?.includes("Delete")
+    )!;
+    fireEvent.click(deleteBtn);
+    expect(mockStoreState.setPendingDelete).toHaveBeenCalledWith(
+      expect.objectContaining({
+        id: "ws-leaf",
+        name: "Leaf",
+        hasChildren: false,
+        children: [],
+      })
+    );
+  });
+});