feat: persist AI chat history to server-side JSON file

Chat history was stored only in sessionStorage, causing member ID and DOB
to be lost when the session expired or corrupted — requiring logout/login.
Now history is saved to a per-user JSON file on the backend and loaded on
mount, so the LLM always has full conversation context.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Backend/src/routes/ai-settings.ts

@@ -1,9 +1,17 @@
 import express, { Request, Response } from "express";
+import fs from "fs";
+import path from "path";
 import { storage } from "../storage";
 import { classifyInternalChat } from "../ai/internal-chat-graph";
 import { runInternalChatWorkflow, createAppointmentToday } from "../ai/internal-chat-workflow";
 import { resolveAiProvider } from "../ai/llm-factory";
 
+const CHAT_HISTORY_DIR = path.join(__dirname, "..", "..", "chat-history");
+
+function getChatHistoryPath(userId: number): string {
+  return path.join(CHAT_HISTORY_DIR, `user-${userId}.json`);
+}
+
 const router = express.Router();
 
 // GET /api/ai/settings
@@ -323,4 +331,45 @@ router.post("/create-appointment-today", async (req: Request, res: Response): Pr
   }
 });
 
+// ─── Chat history persistence (JSON file per user) ──────────────────────────
+
+router.get("/chat-history", async (req: Request, res: Response): Promise<any> => {
+  try {
+    const userId = req.user?.id;
+    if (!userId) return res.status(401).json({ message: "Unauthorized" });
+    const filePath = getChatHistoryPath(userId);
+    if (!fs.existsSync(filePath)) return res.status(200).json({ messages: [] });
+    const raw = fs.readFileSync(filePath, "utf-8");
+    return res.status(200).json(JSON.parse(raw));
+  } catch (err) {
+    return res.status(500).json({ error: "Failed to load chat history", details: String(err) });
+  }
+});
+
+router.put("/chat-history", async (req: Request, res: Response): Promise<any> => {
+  try {
+    const userId = req.user?.id;
+    if (!userId) return res.status(401).json({ message: "Unauthorized" });
+    const { messages } = req.body;
+    if (!Array.isArray(messages)) return res.status(400).json({ message: "messages array is required" });
+    if (!fs.existsSync(CHAT_HISTORY_DIR)) fs.mkdirSync(CHAT_HISTORY_DIR, { recursive: true });
+    fs.writeFileSync(getChatHistoryPath(userId), JSON.stringify({ messages }, null, 2));
+    return res.status(200).json({ ok: true });
+  } catch (err) {
+    return res.status(500).json({ error: "Failed to save chat history", details: String(err) });
+  }
+});
+
+router.delete("/chat-history", async (req: Request, res: Response): Promise<any> => {
+  try {
+    const userId = req.user?.id;
+    if (!userId) return res.status(401).json({ message: "Unauthorized" });
+    const filePath = getChatHistoryPath(userId);
+    if (fs.existsSync(filePath)) fs.unlinkSync(filePath);
+    return res.status(200).json({ ok: true });
+  } catch (err) {
+    return res.status(500).json({ error: "Failed to clear chat history", details: String(err) });
+  }
+});
+
 export default router;