feat: implement R42 chat infrastructure with Anthropic API integration and custom design system

src/lib/api.js

@@ -64,6 +64,61 @@ export const anthropicApi = {
   }
 };
 
+/**
+ * Multi-turn chat with optional tool use.
+ * Returns the raw Anthropic response so callers can read both `text` and
+ * `tool_use` content blocks.
+ *
+ * @param {string} systemPrompt
+ * @param {Array<{role: 'user'|'assistant', content: string}>} messages
+ * @param {{tools?: Array}} opts
+ * @returns {Promise<{content: Array, stop_reason: string}>}
+ */
+anthropicApi.chat = async function chat(systemPrompt, messages, opts = {}) {
+  const useSimulation = storage.get('admin:use_simulation') === true;
+  if (useSimulation) {
+    await new Promise(r => setTimeout(r, 600));
+    return {
+      content: [{
+        type: 'text',
+        text: 'Simulatiemodus staat aan — vraag een beheerder om Simulation Mode uit te zetten in Admin → Settings om met R42 te chatten.',
+      }],
+      stop_reason: 'end_turn',
+    };
+  }
+
+  const model = storage.get('admin:model') || DEFAULT_MODEL;
+
+  const body = {
+    model,
+    max_tokens: 1024,
+    system: systemPrompt,
+    messages,
+  };
+  if (opts.tools && opts.tools.length) body.tools = opts.tools;
+
+  const response = await fetch('/api/anthropic/v1/messages', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'anthropic-version': '2023-06-01',
+    },
+    body: JSON.stringify(body),
+  });
+
+  if (!response.ok) {
+    const errData = await response.json().catch(() => ({}));
+    throw new Error(`API Error: ${response.status} ${response.statusText} - ${JSON.stringify(errData)}`);
+  }
+
+  const contentType = response.headers.get('content-type') || '';
+  if (!contentType.includes('application/json')) {
+    throw new Error('Your session has expired. Please refresh the page and log in again.');
+  }
+
+  return await response.json();
+};
+
 async function simulateResponse() {
   await new Promise(r => setTimeout(r, 2000));
   return JSON.stringify({