refactor: extract parseA2UIBlocks to lib/a2ui.ts; remove unused import re

- Extract parseA2UIBlocks() from A2UIRenderer.tsx into its own
  frontend/src/lib/a2ui.ts module to satisfy react-refresh/only-export-
  components ESLint rule (A2UIRenderer should only export React components)
- Update ChatPanel.tsx and test files to import from lib/a2ui
- Split ChatPanel.test.tsx mock: separate vi.mock for lib/a2ui
  (parseA2UIBlocks) and A2UIRenderer (component only)
- Remove unused 'import re' from tests/test_runtime_html.py (ruff F401)

All 216 frontend tests and 242 bash tests still pass. TypeScript and
Vite builds are clean. Remaining ESLint warnings (react-hooks/set-state-
in-effect in MCPAppRenderer and useSessions) are pre-existing patterns
not introduced by Phase 3.

frontend/src/components/A2UIRenderer.tsx

@@ -230,23 +230,4 @@ export function A2UIRenderer({ block, onAction }: A2UIRendererProps) {
   }
 }
 
-// ─── parseA2UIBlocks ─────────────────────────────────────────────────────────
 
-export function parseA2UIBlocks(content: string): A2UIBlock[] {
-  const blocks: A2UIBlock[] = []
-  const regex = /```a2ui\s*\n([\s\S]*?)```/g
-  let match: RegExpExecArray | null
-
-  while ((match = regex.exec(content)) !== null) {
-    try {
-      const parsed = JSON.parse(match[1])
-      if (parsed && parsed.type) {
-        blocks.push(parsed as A2UIBlock)
-      }
-    } catch {
-      // Silently skip invalid JSON
-    }
-  }
-
-  return blocks
-}

frontend/src/components/ChatPanel.tsx

@@ -4,7 +4,8 @@ import ReactMarkdown from 'react-markdown'
 import { IconSend } from '@tabler/icons-react'
 import { ToolCallCard } from './ToolCallCard'
 import { MCPAppRenderer } from './MCPAppRenderer'
-import { A2UIRenderer, parseA2UIBlocks } from './A2UIRenderer'
+import { A2UIRenderer } from './A2UIRenderer'
+import { parseA2UIBlocks } from '../lib/a2ui'
 import type { ChatMessage } from '../hooks/useChat'
 
 interface ChatPanelProps {

frontend/src/lib/a2ui.ts

@@ -0,0 +1,25 @@
+import type { A2UIBlock } from './types'
+
+/**
+ * Parses `a2ui` fenced code blocks out of a markdown-like content string.
+ * Each block must contain a valid JSON object with a `type` field.
+ * Invalid blocks are silently skipped.
+ */
+export function parseA2UIBlocks(content: string): A2UIBlock[] {
+  const blocks: A2UIBlock[] = []
+  const regex = /```a2ui\s*\n([\s\S]*?)```/g
+  let match: RegExpExecArray | null
+
+  while ((match = regex.exec(content)) !== null) {
+    try {
+      const parsed = JSON.parse(match[1])
+      if (parsed && parsed.type) {
+        blocks.push(parsed as A2UIBlock)
+      }
+    } catch {
+      // Silently skip invalid JSON
+    }
+  }
+
+  return blocks
+}

frontend/src/test/A2UIRenderer.test.tsx

@@ -1,6 +1,7 @@
 import { describe, it, expect, vi } from 'vitest'
 import { render, screen, fireEvent } from '@testing-library/react'
-import { A2UIRenderer, parseA2UIBlocks } from '../components/A2UIRenderer'
+import { A2UIRenderer } from '../components/A2UIRenderer'
+import { parseA2UIBlocks } from '../lib/a2ui'
 import type { A2UIBlock } from '../lib/types'
 
 // Mock @tabler/icons-react so icon SVGs don't cause jsdom issues

frontend/src/test/ChatPanel.test.tsx

@@ -32,8 +32,8 @@ vi.mock('../components/MCPAppRenderer', () => ({
   ),
 }))
 
-// Mock A2UIRenderer module (component + parseA2UIBlocks)
+// Mock lib/a2ui parseA2UIBlocks parser
-vi.mock('../components/A2UIRenderer', () => ({
+vi.mock('../lib/a2ui', () => ({
   parseA2UIBlocks: vi.fn((content: string) => {
     const blocks: Array<Record<string, unknown>> = []
     const regex = /```a2ui\s*\n([\s\S]*?)```/g
@@ -48,6 +48,10 @@ vi.mock('../components/A2UIRenderer', () => ({
     }
     return blocks
   }),
+}))
+
+// Mock A2UIRenderer component
+vi.mock('../components/A2UIRenderer', () => ({
   A2UIRenderer: ({
     block,
     onAction,

tests/test_runtime_html.py

@@ -7,7 +7,7 @@ as specified in task-5.
 """
 
 import os
-import re
+
 import pytest
 
 HTML_FILE = os.path.join(
@@ -31,7 +31,10 @@ class TestFileExists:
         assert os.path.exists(HTML_FILE), f"runtime.html not found at {HTML_FILE}"
 
     def test_is_complete_html_document(self, html_content):
-        assert "<!DOCTYPE html>" in html_content or "<!doctype html>" in html_content.lower()
+        assert (
+            "<!DOCTYPE html>" in html_content
+            or "<!doctype html>" in html_content.lower()
+        )
         assert "<html" in html_content
         assert "</html>" in html_content
 
@@ -40,21 +43,32 @@ class TestCDNLibraries:
     """Verify all required CDN libraries are present in the head section."""
 
     def test_tabler_css_cdn(self, html_content):
-        assert "https://cdn.jsdelivr.net/npm/@tabler/core@1.0.0-beta20/dist/css/tabler.min.css" in html_content
+        assert (
+            "https://cdn.jsdelivr.net/npm/@tabler/core@1.0.0-beta20/dist/css/tabler.min.css"
+            in html_content
+        )
 
     def test_leaflet_css_cdn(self, html_content):
-        assert "https://cdn.jsdelivr.net/npm/leaflet@1.9/dist/leaflet.css" in html_content
+        assert (
+            "https://cdn.jsdelivr.net/npm/leaflet@1.9/dist/leaflet.css" in html_content
+        )
 
     def test_chartjs_cdn(self, html_content):
         assert "https://cdn.jsdelivr.net/npm/chart.js@4" in html_content
 
     def test_leaflet_js_cdn(self, html_content):
-        assert "https://cdn.jsdelivr.net/npm/leaflet@1.9/dist/leaflet.js" in html_content
+        assert (
+            "https://cdn.jsdelivr.net/npm/leaflet@1.9/dist/leaflet.js" in html_content
+        )
 
     def test_react_19_umd(self, html_content):
         # React 19 production UMD
         assert "react@19" in html_content
-        assert "umd" in html_content.lower() or "unpkg.com" in html_content or "cdn.jsdelivr.net" in html_content
+        assert (
+            "umd" in html_content.lower()
+            or "unpkg.com" in html_content
+            or "cdn.jsdelivr.net" in html_content
+        )
 
     def test_react_dom_19_umd(self, html_content):
         # ReactDOM 19 production UMD
@@ -73,7 +87,9 @@ class TestStyles:
         assert "transparent" in html_content
 
     def test_dark_color_scheme(self, html_content):
-        assert "color-scheme: dark" in html_content or "color-scheme:dark" in html_content
+        assert (
+            "color-scheme: dark" in html_content or "color-scheme:dark" in html_content
+        )
 
     def test_body_padding_16px(self, html_content):
         assert "16px" in html_content
@@ -83,7 +99,11 @@ class TestStyles:
 
     def test_visual_error_red_color(self, html_content):
         # red text color for error class
-        assert "#ff" in html_content.lower() or "red" in html_content or "color: #" in html_content
+        assert (
+            "#ff" in html_content.lower()
+            or "red" in html_content
+            or "color: #" in html_content
+        )
 
     def test_visual_error_monospace(self, html_content):
         assert "monospace" in html_content
@@ -118,7 +138,11 @@ class TestMcpBridge:
 
     def test_call_tool_jsonrpc_20(self, html_content):
         # jsonrpc key may appear as unquoted JS property (jsonrpc:) or quoted ("jsonrpc" / 'jsonrpc')
-        assert '"jsonrpc"' in html_content or "'jsonrpc'" in html_content or "jsonrpc:" in html_content
+        assert (
+            '"jsonrpc"' in html_content
+            or "'jsonrpc'" in html_content
+            or "jsonrpc:" in html_content
+        )
         assert '"2.0"' in html_content or "'2.0'" in html_content
 
     def test_call_tool_method_name(self, html_content):
@@ -129,7 +153,11 @@ class TestMcpBridge:
 
     def test_call_tool_uses_uuid(self, html_content):
         # Random UUID for call id
-        assert "crypto" in html_content or "Math.random" in html_content or "uuid" in html_content.lower()
+        assert (
+            "crypto" in html_content
+            or "Math.random" in html_content
+            or "uuid" in html_content.lower()
+        )
 
     def test_send_message_method(self, html_content):
         assert "sendMessage" in html_content
@@ -169,7 +197,7 @@ class TestExecuteVisual:
 
     def test_jsx_detection_type_text_babel(self, html_content):
         # The regex pattern in JS source: /type="text\/babel"/ contains text\/babel
-        assert 'text/babel' in html_content or r'text\/babel' in html_content
+        assert "text/babel" in html_content or r"text\/babel" in html_content
 
     def test_jsx_path_uses_babel_transform(self, html_content):
         assert "Babel.transform" in html_content
@@ -200,7 +228,11 @@ class TestExecuteVisual:
         assert "new Function" in html_content
 
     def test_plain_js_passes_chart_arg(self, html_content):
-        assert '"Chart"' in html_content or "'Chart'" in html_content or "Chart" in html_content
+        assert (
+            '"Chart"' in html_content
+            or "'Chart'" in html_content
+            or "Chart" in html_content
+        )
 
     def test_plain_js_passes_leaflet_arg(self, html_content):
         assert '"L"' in html_content or "'L'" in html_content
@@ -270,4 +302,6 @@ class TestInitialHandshake:
         assert "1.0.0" in html_content
 
     def test_handshake_uses_send_to_host(self, html_content):
-        assert "sendToHost" in html_content or "window.parent.postMessage" in html_content
+        assert (
+            "sendToHost" in html_content or "window.parent.postMessage" in html_content
+        )