Proxy /api/v1 and /api/auth from Hono to FastAPI in prod

In production the browser talks to the Hono server, which only proxied
/api/copilotkit/*. All other /api/* requests hit the SPA static fallback
and got index.html back. Forward /api/v1/* and /api/auth/* to BACKEND_URL.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/server.ts

@@ -11,6 +11,8 @@ import { Hono } from "hono";
 
 const AGENT_URL =
   process.env.AGENT_URL ?? "http://backend:8000/api/v1/agent/agui";
+const BACKEND_URL =
+  process.env.BACKEND_URL ?? "http://localhost:8001";
 
 const isProd = process.env.NODE_ENV === "production";
 const PORT = parseInt(process.env.PORT ?? (isProd ? "3000" : "3001"));
@@ -376,6 +378,32 @@ app.all("/api/copilotkit/*", async (c) => {
 
 app.get("/api/health", (c) => c.json({ ok: true }));
 
+// Proxy backend API calls (FastAPI). In dev these hit Vite's proxy directly,
+// but in prod the browser talks to this Hono server, which must forward
+// `/api/v1/*` and `/api/auth/*` to the FastAPI container — otherwise the SPA
+// fallback below swallows them and returns index.html.
+const proxyToBackend = async (c: import("hono").Context) => {
+  const url = new URL(c.req.url);
+  const target = `${BACKEND_URL}${url.pathname}${url.search}`;
+  const method = c.req.method;
+  const headers = new Headers(c.req.raw.headers);
+  headers.delete("host");
+  const init: RequestInit = {
+    method,
+    headers,
+    redirect: "manual",
+  };
+  if (method !== "GET" && method !== "HEAD") {
+    init.body = c.req.raw.body;
+    // @ts-expect-error undici requires duplex for streamed bodies
+    init.duplex = "half";
+  }
+  return fetch(target, init);
+};
+
+app.all("/api/v1/*", proxyToBackend);
+app.all("/api/auth/*", proxyToBackend);
+
 // In production, serve the Vite build output.
 if (isProd) {
   app.use("/*", serveStatic({ root: "./dist" }));