feat: implement DS2API_HISTORY.txt transcript parser to merge history into chat messages

tests/node/chat-history-utils.test.js

@@ -58,3 +58,47 @@ test('chat history strict parser inserts history after system messages', async (
     { role: 'user', content: 'latest' },
   ]);
 });
+
+test('chat history transcript parser replaces current input file placeholder', async () => {
+  const {
+    buildListModeMessages,
+  } = await loadUtils();
+  const t = (key) => key;
+  const item = {
+    messages: [{
+      role: 'user',
+      content: 'Continue from the latest state in the attached DS2API_HISTORY.txt context. Treat it as the current working state and answer the latest user request directly.',
+    }],
+    history_text: [
+      '# DS2API_HISTORY.txt',
+      'Prior conversation history and tool progress.',
+      '',
+      '=== 1. SYSTEM ===',
+      'policy',
+      '',
+      '=== 2. USER ===',
+      'hello',
+      '',
+      '=== 3. ASSISTANT ===',
+      'hi',
+      '',
+      '=== 4. TOOL ===',
+      '[name=search_web tool_call_id=call_1]',
+      '{"ok":true}',
+      '',
+      '=== 5. USER ===',
+      'latest',
+      '',
+    ].join('\n'),
+  };
+
+  const result = buildListModeMessages(item, t);
+  assert.equal(result.historyMerged, true);
+  assert.deepEqual(result.messages, [
+    { role: 'system', content: 'policy' },
+    { role: 'user', content: 'hello' },
+    { role: 'assistant', content: 'hi' },
+    { role: 'tool', content: '[name=search_web tool_call_id=call_1]\n{"ok":true}' },
+    { role: 'user', content: 'latest' },
+  ]);
+});