feat: chat API route proxying to gateway with offline fallback

app/api/chat/route.ts

@@ -0,0 +1,42 @@
+import { NextRequest, NextResponse } from "next/server";
+
+const GATEWAY = process.env.BLACKROAD_GATEWAY_URL ?? "http://127.0.0.1:8787";
+
+export async function POST(req: NextRequest) {
+  const body = await req.json();
+
+  try {
+    const upstream = await fetch(`${GATEWAY}/v1/chat`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(body),
+    });
+
+    // Stream back if gateway sends SSE
+    if (upstream.headers.get("content-type")?.includes("text/event-stream")) {
+      return new NextResponse(upstream.body, {
+        status: 200,
+        headers: {
+          "Content-Type": "text/event-stream",
+          "Cache-Control": "no-cache",
+          "X-Accel-Buffering": "no",
+        },
+      });
+    }
+
+    const data = await upstream.json();
+    return NextResponse.json(data, { status: upstream.status });
+  } catch {
+    // Offline graceful degradation
+    return NextResponse.json(
+      {
+        role: "assistant",
+        content:
+          "Gateway offline. To enable live AI responses, start the BlackRoad gateway: `br gateway start`",
+        agent: body.agent ?? "SYSTEM",
+        offline: true,
+      },
+      { status: 200 }
+    );
+  }
+}