refactor: extract shared message parsing helpers into lib/messageExtract

- Move extractText and extractThinking from useGateway and useSecondarySession into shared lib
- Add comprehensive unit tests (13 tests) for both functions
- Eliminate code duplication between the two hooks

src/hooks/useGateway.ts

@@ -5,35 +5,9 @@ import { getStoredCredentials, storeCredentials, clearCredentials, type AuthMode
 import { getOrCreateDeviceIdentity } from '../lib/deviceIdentity';
 import { isSystemEvent } from '../lib/systemEvent';
 import { getCachedMessages, setCachedMessages, mergeWithCache } from '../lib/messageCache';
+import { extractText, extractThinking, type ChatPayloadMessage } from '../lib/messageExtract';
 import type { ChatMessage, MessageBlock, ConnectionStatus, Session, AgentIdentity } from '../types';
 
-interface ChatPayloadMessage {
-  content?: string | Array<{ type: string; text?: string; thinking?: string }>;
-}
-
-function extractText(message: ChatPayloadMessage | undefined): string {
-  if (!message) return '';
-  const content = message.content;
-  if (typeof content === 'string') return content;
-  if (Array.isArray(content)) {
-    return content
-      .filter((b) => b.type === 'text' && typeof b.text === 'string')
-      .map((b) => b.text as string)
-      .join('\n');
-  }
-  return '';
-}
-
-function extractThinking(message: ChatPayloadMessage | undefined): string {
-  if (!message) return '';
-  const content = message.content;
-  if (!Array.isArray(content)) return '';
-  return content
-    .filter((b) => b.type === 'thinking')
-    .map((b) => b.thinking || b.text || '')
-    .join('\n');
-}
-
 export function useGateway() {
   const clientRef = useRef<GatewayClient | null>(null);
   const [status, setStatus] = useState<ConnectionStatus>('disconnected');

src/hooks/useSecondarySession.ts

@@ -2,33 +2,8 @@ import { useState, useCallback, useEffect, useRef } from 'react';
 import type { GatewayClient, JsonPayload } from '../lib/gateway';
 import type { ChatMessage, MessageBlock } from '../types';
 import { isSystemEvent } from '../lib/systemEvent';
-
-interface ChatPayloadMessage {
-  content?: string | Array<{ type: string; text?: string; thinking?: string }>;
-}
-
-function extractText(message: ChatPayloadMessage | undefined): string {
-  if (!message) return '';
-  const content = message.content;
-  if (typeof content === 'string') return content;
-  if (Array.isArray(content)) {
-    return content
-      .filter((b) => b.type === 'text' && typeof b.text === 'string')
-      .map((b) => b.text as string)
-      .join('\n');
-  }
-  return '';
-}
-
-function extractThinking(message: ChatPayloadMessage | undefined): string {
-  if (!message) return '';
-  const content = message.content;
-  if (!Array.isArray(content)) return '';
-  return content
-    .filter((b) => b.type === 'thinking')
-    .map((b) => b.thinking || b.text || '')
-    .join('\n');
-}
+import { extractText, extractThinking } from '../lib/messageExtract';
+import type { ChatPayloadMessage } from '../lib/messageExtract';
 
 /**
  * Hook to manage a secondary session for split view.

src/lib/__tests__/messageExtract.test.ts

@@ -0,0 +1,90 @@
+import { describe, it, expect } from 'vitest';
+import { extractText, extractThinking } from '../messageExtract';
+
+describe('extractText', () => {
+  it('returns empty string for undefined', () => {
+    expect(extractText(undefined)).toBe('');
+  });
+
+  it('returns empty string for empty message', () => {
+    expect(extractText({})).toBe('');
+  });
+
+  it('returns string content directly', () => {
+    expect(extractText({ content: 'hello world' })).toBe('hello world');
+  });
+
+  it('extracts text blocks from array content', () => {
+    expect(extractText({
+      content: [
+        { type: 'text', text: 'hello' },
+        { type: 'thinking', thinking: 'hmm' },
+        { type: 'text', text: 'world' },
+      ],
+    })).toBe('hello\nworld');
+  });
+
+  it('ignores non-text blocks', () => {
+    expect(extractText({
+      content: [
+        { type: 'thinking', text: 'reasoning' },
+        { type: 'image', text: 'img' },
+      ],
+    })).toBe('');
+  });
+
+  it('skips text blocks with undefined text', () => {
+    expect(extractText({
+      content: [
+        { type: 'text' },
+        { type: 'text', text: 'ok' },
+      ],
+    })).toBe('ok');
+  });
+
+  it('returns empty string for non-string non-array content', () => {
+    expect(extractText({ content: 42 as unknown as string })).toBe('');
+  });
+});
+
+describe('extractThinking', () => {
+  it('returns empty string for undefined', () => {
+    expect(extractThinking(undefined)).toBe('');
+  });
+
+  it('returns empty string for string content', () => {
+    expect(extractThinking({ content: 'hello' })).toBe('');
+  });
+
+  it('extracts thinking blocks using thinking field', () => {
+    expect(extractThinking({
+      content: [
+        { type: 'text', text: 'hello' },
+        { type: 'thinking', thinking: 'let me think' },
+      ],
+    })).toBe('let me think');
+  });
+
+  it('falls back to text field when thinking is absent', () => {
+    expect(extractThinking({
+      content: [
+        { type: 'thinking', text: 'fallback' },
+      ],
+    })).toBe('fallback');
+  });
+
+  it('joins multiple thinking blocks', () => {
+    expect(extractThinking({
+      content: [
+        { type: 'thinking', thinking: 'step 1' },
+        { type: 'thinking', thinking: 'step 2' },
+      ],
+    })).toBe('step 1\nstep 2');
+  });
+
+  it('returns empty string for thinking block with no content', () => {
+    expect(extractThinking({
+      content: [{ type: 'thinking' }],
+    })).toBe('');
+  });
+});

src/lib/messageExtract.ts

@@ -0,0 +1,32 @@
+/**
+ * Shared helpers for extracting text and thinking content from gateway chat messages.
+ */
+
+export interface ChatPayloadMessage {
+  content?: string | Array<{ type: string; text?: string; thinking?: string }>;
+}
+
+/** Extract all text blocks from a gateway chat message, joined by newline. */
+export function extractText(message: ChatPayloadMessage | undefined): string {
+  if (!message) return '';
+  const content = message.content;
+  if (typeof content === 'string') return content;
+  if (Array.isArray(content)) {
+    return content
+      .filter((b) => b.type === 'text' && typeof b.text === 'string')
+      .map((b) => b.text as string)
+      .join('\n');
+  }
+  return '';
+}
+
+/** Extract all thinking blocks from a gateway chat message, joined by newline. */
+export function extractThinking(message: ChatPayloadMessage | undefined): string {
+  if (!message) return '';
+  const content = message.content;
+  if (!Array.isArray(content)) return '';
+  return content
+    .filter((b) => b.type === 'thinking')
+    .map((b) => b.thinking || b.text || '')
+    .join('\n');
+}