Chat: show why the AI could not answer

chat/chat.js

@@ -249,7 +249,7 @@ async function ask(question) {
 // Write (or rewrite) an answer with the model; the GPU can be lost (memory pressure, sleep): restart once, else keep the quick answer.
 async function aiAnswer(chat, reply, messages, passages) {
   const index = chat.messages.indexOf(reply);
-  let engine = state.engine;
+  let engine = state.engine, lastError = '';
   for (let attempt = 0; attempt < 2 && engine; attempt++) {
     try {
       const stream = await engine.chat.completions.create({ messages, temperature: 0, max_tokens: 700, stream: true });
@@ -285,13 +285,14 @@ async function aiAnswer(chat, reply, messages, passages) {
       if (chatProblems(messages[messages.length - 1].content, reply.content).length) reply.note = 'Some details in this answer could not be matched to the sources. Check them in the sources below before acting.';
       return;
     } catch (error) {
+      lastError = error.message;
       if (!/lost|Instance reference|GPUDevice|disposed/i.test(error.message)) { console.warn('AI answer failed', error); break; }  // keep the quick answer
       status('The graphics processor was reset; restarting the AI…', 0.5);
       state.engine = null; state.enginePromise = null;
       engine = attempt === 0 ? await getEngine() : null;
     }
   }
-  fallback(reply, passages, 'Quick answer from the knowledge base (the AI could not run just now).');
+  fallback(reply, passages, `Quick answer from the knowledge base (the AI could not run just now${lastError ? `: ${lastError.slice(0, 140)}` : ''}).`);
 }
 
 function fallback(reply, passages, note) {