feat: add OpenCode session management

backend/src/title-generator.js

@@ -155,12 +155,26 @@ function fetchAgyMessages(session) {
   return result;
 }
 
+/** Fetch OpenCode messages via adapter (reuses parsed message format). */
+async function fetchOpenCodeMessages(sessionId, adapter) {
+  try {
+    const messages = await adapter.getMessages(sessionId);
+    return messages
+      .filter(m => m.type === 'user_message' || m.type === 'assistant_message')
+      .map(m => ({ type: m.type, message: (m.message || '').slice(0, 2000) }));
+  } catch (err) {
+    console.warn(`[TitleGen] OpenCode fetch error for ${sessionId.slice(0, 16)}:`, err.message);
+    return [];
+  }
+}
+
 async function fetchMessages(engine, sessionId, adapter) {
   const session = adapter ? adapter.getSession(sessionId) : null;
   if (!session) return [];
   if (engine === 'codex') return await fetchCodexMessages(session);
   if (engine === 'claude') return await fetchClaudeMessages(sessionId);
   if (engine === 'agy') return fetchAgyMessages(session);
+  if (engine === 'opencode') return await fetchOpenCodeMessages(sessionId, adapter);
   return [];
 }