diff --git a/apps/web/src/components/mindmap/ReactFlowEditor.test.tsx b/apps/web/src/components/mindmap/ReactFlowEditor.test.tsx
new file mode 100644
index 0000000..c1c80b0
--- /dev/null
+++ b/apps/web/src/components/mindmap/ReactFlowEditor.test.tsx
@@ -0,0 +1,270 @@
+/**
+ * ReactFlowEditor Tests
+ * Tests for the boolean logic in handleDeleteSelected
+ * - When readOnly=false AND selectedNode=null, editing should be disabled
+ * - When readOnly=false AND selectedNode exists, editing should be enabled
+ * - When readOnly=true, editing should always be disabled
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/react";
+import { ReactFlowEditor } from "./ReactFlowEditor";
+import type { GraphData } from "./hooks/useGraphData";
+
+// Mock ReactFlow since it requires DOM APIs not available in test environment
+vi.mock("@xyflow/react", () => ({
+  ReactFlow: ({
+    nodes,
+    edges,
+    children,
+    onNodeClick,
+    onPaneClick,
+  }: {
+    nodes: unknown[];
+    edges: unknown[];
+    children: React.ReactNode;
+    onNodeClick?: (event: React.MouseEvent, node: { id: string }) => void;
+    onPaneClick?: () => void;
+  }): React.JSX.Element => (
+    <div data-testid="react-flow">
+      <div data-testid="node-count">{nodes.length}</div>
+      <div data-testid="edge-count">{edges.length}</div>
+      {/* Simulate node click for testing */}
+      <button
+        data-testid="mock-node-click"
+        onClick={(e): void => {
+          if (onNodeClick) {
+            onNodeClick(e as unknown as React.MouseEvent, { id: "node-1" });
+          }
+        }}
+      >
+        Click Node
+      </button>
+      {/* Simulate pane click for deselection */}
+      <button
+        data-testid="mock-pane-click"
+        onClick={(): void => {
+          if (onPaneClick) {
+            onPaneClick();
+          }
+        }}
+      >
+        Click Pane
+      </button>
+      {children}
+    </div>
+  ),
+  Background: (): React.JSX.Element => <div data-testid="background" />,
+  Controls: (): React.JSX.Element => <div data-testid="controls" />,
+  MiniMap: (): React.JSX.Element => <div data-testid="minimap" />,
+  Panel: ({
+    children,
+    position,
+  }: {
+    children: React.ReactNode;
+    position: string;
+  }): React.JSX.Element => <div data-testid={`panel-${position}`}>{children}</div>,
+  useNodesState: (initial: unknown[]): [unknown[], () => void, () => void] => [
+    initial,
+    vi.fn(),
+    vi.fn(),
+  ],
+  useEdgesState: (initial: unknown[]): [unknown[], () => void, () => void] => [
+    initial,
+    vi.fn(),
+    vi.fn(),
+  ],
+  addEdge: vi.fn(),
+  MarkerType: { ArrowClosed: "arrowclosed" },
+  BackgroundVariant: { Dots: "dots" },
+}));
+
+const mockGraphData: GraphData = {
+  nodes: [
+    {
+      id: "node-1",
+      title: "Test Node 1",
+      content: "Content 1",
+      node_type: "concept",
+      tags: ["test"],
+      domain: "test",
+      metadata: {},
+      created_at: new Date().toISOString(),
+      updated_at: new Date().toISOString(),
+    },
+    {
+      id: "node-2",
+      title: "Test Node 2",
+      content: "Content 2",
+      node_type: "task",
+      tags: ["test"],
+      domain: "test",
+      metadata: {},
+      created_at: new Date().toISOString(),
+      updated_at: new Date().toISOString(),
+    },
+  ],
+  edges: [
+    {
+      source_id: "node-1",
+      target_id: "node-2",
+      relation_type: "relates_to",
+      weight: 1.0,
+      metadata: {},
+      created_at: new Date().toISOString(),
+    },
+  ],
+};
+
+describe("ReactFlowEditor", (): void => {
+  beforeEach((): void => {
+    vi.clearAllMocks();
+  });
+
+  describe("rendering", (): void => {
+    it("should render the graph with nodes and edges", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} />);
+
+      expect(screen.getByTestId("react-flow")).toBeInTheDocument();
+      expect(screen.getByTestId("node-count")).toHaveTextContent("2");
+      expect(screen.getByTestId("edge-count")).toHaveTextContent("1");
+    });
+
+    it("should render controls and minimap", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} />);
+
+      expect(screen.getByTestId("controls")).toBeInTheDocument();
+      expect(screen.getByTestId("minimap")).toBeInTheDocument();
+    });
+
+    it("should display node and edge counts in panel", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} />);
+
+      expect(screen.getByText("2 nodes, 1 edges")).toBeInTheDocument();
+    });
+  });
+
+  describe("handleDeleteSelected boolean logic (CQ-WEB-5 fix)", (): void => {
+    it("should NOT show delete button when readOnly=false AND no node is selected", (): void => {
+      // This tests the core bug fix: when readOnly=false but selectedNode=null,
+      // the delete button should NOT appear because there's nothing to delete.
+      // The bug was using ?? instead of || which would fail this case.
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={false} />);
+
+      // No node selected initially, delete button should not appear
+      expect(screen.queryByRole("button", { name: /delete node/i })).not.toBeInTheDocument();
+    });
+
+    it("should show delete button when readOnly=false AND a node is selected", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={false} />);
+
+      // Initially no delete button
+      expect(screen.queryByRole("button", { name: /delete node/i })).not.toBeInTheDocument();
+
+      // Select a node
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+
+      // Now delete button should appear
+      expect(screen.getByRole("button", { name: /delete node/i })).toBeInTheDocument();
+    });
+
+    it("should NOT show delete button when readOnly=true even with a node selected", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={true} />);
+
+      // Select a node
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+
+      // Delete button should NOT appear in readOnly mode
+      expect(screen.queryByRole("button", { name: /delete node/i })).not.toBeInTheDocument();
+    });
+
+    it("should hide delete button when node is deselected", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={false} />);
+
+      // Select a node
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+      expect(screen.getByRole("button", { name: /delete node/i })).toBeInTheDocument();
+
+      // Click on pane to deselect
+      fireEvent.click(screen.getByTestId("mock-pane-click"));
+
+      // Delete button should disappear
+      expect(screen.queryByRole("button", { name: /delete node/i })).not.toBeInTheDocument();
+    });
+
+    it("should call onNodeDelete when delete button is clicked with valid selection", (): void => {
+      const onNodeDelete = vi.fn();
+      render(
+        <ReactFlowEditor graphData={mockGraphData} readOnly={false} onNodeDelete={onNodeDelete} />
+      );
+
+      // Select a node
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+
+      // Click delete button
+      fireEvent.click(screen.getByRole("button", { name: /delete node/i }));
+
+      // onNodeDelete should be called with the node id
+      expect(onNodeDelete).toHaveBeenCalledWith("node-1");
+    });
+
+    it("should NOT call onNodeDelete in readOnly mode even if somehow triggered", (): void => {
+      // This tests that the handleDeleteSelected function early-returns
+      // when readOnly is true, providing defense in depth
+      const onNodeDelete = vi.fn();
+      render(
+        <ReactFlowEditor graphData={mockGraphData} readOnly={true} onNodeDelete={onNodeDelete} />
+      );
+
+      // Even if we try to select a node, readOnly should prevent deletion
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+
+      // No delete button should exist
+      expect(screen.queryByRole("button", { name: /delete node/i })).not.toBeInTheDocument();
+
+      // And the callback should never have been called
+      expect(onNodeDelete).not.toHaveBeenCalled();
+    });
+  });
+
+  describe("node selection", (): void => {
+    it("should call onNodeSelect when a node is clicked", (): void => {
+      const onNodeSelect = vi.fn();
+      render(<ReactFlowEditor graphData={mockGraphData} onNodeSelect={onNodeSelect} />);
+
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+
+      expect(onNodeSelect).toHaveBeenCalledWith(mockGraphData.nodes[0]);
+    });
+
+    it("should call onNodeSelect with null when pane is clicked", (): void => {
+      const onNodeSelect = vi.fn();
+      render(<ReactFlowEditor graphData={mockGraphData} onNodeSelect={onNodeSelect} />);
+
+      // First select a node
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+      expect(onNodeSelect).toHaveBeenCalledWith(mockGraphData.nodes[0]);
+
+      // Then click on pane to deselect
+      fireEvent.click(screen.getByTestId("mock-pane-click"));
+      expect(onNodeSelect).toHaveBeenLastCalledWith(null);
+    });
+  });
+
+  describe("readOnly mode", (): void => {
+    it("should hide interactive controls when readOnly is true", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={true} />);
+
+      // The delete panel should not appear even after clicking
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+      expect(screen.queryByText("Delete Node")).not.toBeInTheDocument();
+    });
+
+    it("should show interactive controls when readOnly is false and node is selected", (): void => {
+      render(<ReactFlowEditor graphData={mockGraphData} readOnly={false} />);
+
+      fireEvent.click(screen.getByTestId("mock-node-click"));
+      expect(screen.getByRole("button", { name: /delete node/i })).toBeInTheDocument();
+    });
+  });
+});
diff --git a/apps/web/src/components/mindmap/ReactFlowEditor.tsx b/apps/web/src/components/mindmap/ReactFlowEditor.tsx
index c8b8905..5801e1b 100644
--- a/apps/web/src/components/mindmap/ReactFlowEditor.tsx
+++ b/apps/web/src/components/mindmap/ReactFlowEditor.tsx
@@ -1,4 +1,3 @@
-/* eslint-disable @typescript-eslint/no-unnecessary-condition */
 "use client";
 
 import { useCallback, useEffect, useMemo, useState } from "react";
@@ -211,7 +210,7 @@ export function ReactFlowEditor({
   );
 
   const handleDeleteSelected = useCallback(() => {
-    if (readOnly ?? !selectedNode) return;
+    if (readOnly || !selectedNode) return;
 
     if (onNodeDelete) {
       onNodeDelete(selectedNode);