feat: add markdown composer backend foundation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/shared/chatMessage.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  hasMeaningfulChatMessageContent,
+  normalizeChatMessageLineEndings,
+  prepareChatMessageContent,
+} from '@shared/utils/chatMessage';
+
+describe('chat message helpers', () => {
+  test('normalizes Windows line endings without trimming meaningful markdown', () => {
+    expect(
+      prepareChatMessageContent('```ts\r\n  const answer = 42;\r\n```\r\n'),
+    ).toBe('```ts\n  const answer = 42;\n```\n');
+  });
+
+  test('treats whitespace-only input as empty', () => {
+    expect(hasMeaningfulChatMessageContent(' \r\n\t ')).toBe(false);
+    expect(prepareChatMessageContent(' \r\n\t ')).toBeUndefined();
+  });
+
+  test('normalizes mixed newline sequences consistently', () => {
+    expect(normalizeChatMessageLineEndings('line 1\r\nline 2\rline 3')).toBe(
+      'line 1\nline 2\nline 3',
+    );
+  });
+});

tests/shared/markdownText.test.ts

@@ -0,0 +1,21 @@
+import { describe, expect, test } from 'bun:test';
+
+import { buildMarkdownExcerpt, extractPlainTextFromMarkdown } from '@shared/utils/markdownText';
+
+describe('markdown text helpers', () => {
+  test('extracts readable text from common markdown syntax', () => {
+    expect(
+      extractPlainTextFromMarkdown('# Title\n\n**Bold** [Docs](https://example.com) and `code`.'),
+    ).toBe('Title Bold Docs and code.');
+  });
+
+  test('turns fenced code blocks into readable excerpts', () => {
+    expect(buildMarkdownExcerpt('```ts\nconst answer = 42;\n```', 48)).toBe('const answer = 42;');
+  });
+
+  test('truncates after stripping markdown syntax', () => {
+    expect(buildMarkdownExcerpt('**Alpha** beta gamma delta epsilon zeta eta theta', 18)).toBe(
+      'Alpha beta gamma d…',
+    );
+  });
+});

tests/shared/session.test.ts

@@ -121,6 +121,23 @@ describe('session title helpers', () => {
       ]),
     ).toBe('Release readiness review');
   });
+
+  test('builds auto titles from markdown-heavy first messages', () => {
+    const pattern = createPattern();
+    const session = createSession();
+
+    expect(
+      resolveSessionTitle(session, pattern, [
+        {
+          id: 'msg-1',
+          role: 'user',
+          authorName: 'You',
+          content: '```ts\nconst answer = 42;\n```',
+          createdAt: '2026-03-23T00:00:00.000Z',
+        },
+      ]),
+    ).toBe('const answer = 42;');
+  });
 });
 
 describe('session tooling helpers', () => {