refactor(comments): extract CommentMessage component from CommentThread (#198)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/utils/comment.spec.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect } from 'vitest';
+import { extractQuote } from './comment';
+
+describe('extractQuote', () => {
+	it('returns null quote and full body for plain text', () => {
+		const result = extractQuote('Hello world');
+		expect(result.quote).toBeNull();
+		expect(result.body).toBe('Hello world');
+	});
+
+	it('extracts quote and body with double newline separator', () => {
+		const result = extractQuote('> "Some quoted text"\n\nReply body');
+		expect(result.quote).toBe('Some quoted text');
+		expect(result.body).toBe('Reply body');
+	});
+
+	it('extracts quote and body with single newline separator', () => {
+		const result = extractQuote('> "Quote"\nBody');
+		expect(result.quote).toBe('Quote');
+		expect(result.body).toBe('Body');
+	});
+
+	it('returns null quote when format does not match', () => {
+		const result = extractQuote('> Not a quote format');
+		expect(result.quote).toBeNull();
+		expect(result.body).toBe('> Not a quote format');
+	});
+
+	it('handles empty string', () => {
+		const result = extractQuote('');
+		expect(result.quote).toBeNull();
+		expect(result.body).toBe('');
+	});
+
+	it('does not match when quotes are missing', () => {
+		const result = extractQuote('> just a blockquote\n\nbody');
+		expect(result.quote).toBeNull();
+		expect(result.body).toBe('> just a blockquote\n\nbody');
+	});
+});

frontend/src/lib/utils/comment.ts

@@ -0,0 +1,5 @@
+export function extractQuote(content: string): { quote: string | null; body: string } {
+	const match = content.match(/^>\s*"(.+?)"\s*\n\n?([\s\S]*)$/);
+	if (match) return { quote: match[1], body: match[2] };
+	return { quote: null, body: content };
+}