feat: vite dev server with HMR for dashboard

packages/dashboard/src/server.ts

@@ -1,6 +1,7 @@
 import express from "express";
 import { join, dirname } from "node:path";
 import { existsSync } from "node:fs";
+import { readFile } from "node:fs/promises";
 import { fileURLToPath } from "node:url";
 import type { TaskStore, MergeResult } from "@hai/core";
 import { createApiRoutes } from "./routes.js";
@@ -13,31 +14,51 @@ export interface ServerOptions {
   onMerge?: (taskId: string) => Promise<MergeResult>;
   /** Maximum concurrent worktrees / execution slots (default 2) */
   maxConcurrent?: number;
+  /** Enable Vite dev server with HMR (default: false) */
+  dev?: boolean;
 }
 
-export function createServer(store: TaskStore, options?: ServerOptions): ReturnType<typeof express> {
+export async function createServer(store: TaskStore, options?: ServerOptions) {
   const app = express();
-
   app.use(express.json());
-  // Serve built React app — check both possible locations
-  const clientDir = existsSync(join(__dirname, "..", "dist", "client"))
-    ? join(__dirname, "..", "dist", "client")
-    : existsSync(join(__dirname, "..", "client"))
-      ? join(__dirname, "..", "client")
-      : join(__dirname, "..", "public"); // fallback to old public dir
 
-  app.use(express.static(clientDir));
-
-  // SSE endpoint
+  // SSE endpoint (before Vite middleware so it's not intercepted)
   app.get("/api/events", createSSE(store));
 
   // REST API
   app.use("/api", createApiRoutes(store, options));
 
-  // SPA fallback
-  app.get("/{*splat}", (_req, res) => {
-    res.sendFile(join(clientDir, "index.html"));
-  });
+  if (options?.dev) {
+    // Dev mode: Vite middleware with HMR
+    const { createServer: createViteServer } = await import("vite");
+    const appDir = join(__dirname, "..", "app");
+    const vite = await createViteServer({
+      root: appDir,
+      server: { middlewareMode: true },
+      appType: "custom",
+    });
+    app.use(vite.middlewares);
+
+    // SPA fallback — serve index.html through Vite's transform pipeline
+    app.use(async (_req, res) => {
+      const htmlPath = join(appDir, "index.html");
+      let html = await readFile(htmlPath, "utf-8");
+      html = await vite.transformIndexHtml(_req.originalUrl, html);
+      res.status(200).set({ "Content-Type": "text/html" }).end(html);
+    });
+  } else {
+    // Production: serve pre-built static files
+    const clientDir = existsSync(join(__dirname, "..", "dist", "client"))
+      ? join(__dirname, "..", "dist", "client")
+      : existsSync(join(__dirname, "..", "client"))
+        ? join(__dirname, "..", "client")
+        : join(__dirname, "..", "public");
+
+    app.use(express.static(clientDir));
+    app.get("/{*splat}", (_req, res) => {
+      res.sendFile(join(clientDir, "index.html"));
+    });
+  }
 
   return app;
 }