Minimal example: async render API with SSE streaming (varg render service Phase 4)

gistfile0.txt

# Async Render API — Minimal Example
#
# The render service now returns 202 immediately and processes in the background.
# Use polling or SSE to wait for completion.

## 1. Submit a render (202 instant response)

```bash
curl -s -X POST https://render-fqb8zg.fly.dev/api/render \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $VARG_SERVICE_KEY" \
  -d '{
    "code": "export default <Render><Clip><Image prompt=\"a cat in space\" /></Clip></Render>;",
    "gatewayApiKey": "varg_xxx",
    "mode": "preview"
  }'
```

Response (instant, <200ms):
```json
{ "job_id": "5f650644-fdba-47d5-b889-06b6be92826f", "status": "rendering" }
```

## 2a. Option A — Poll for completion

```bash
curl -s -H "Authorization: Bearer $VARG_SERVICE_KEY" \
  https://render-fqb8zg.fly.dev/api/render/jobs/5f650644-fdba-47d5-b889-06b6be92826f
```

While rendering:
```json
{ "job_id": "5f650644-...", "status": "rendering", "created_at": "..." }
```

When done:
```json
{
  "job_id": "5f650644-...",
  "status": "completed",
  "output_url": "https://s3.varg.ai/renders/xxx.mp4",
  "files": [{ "url": "...", "mediaType": "image/png", "metadata": { "type": "image", "model": "flux-schnell", "prompt": "a cat in space" } }],
  "duration_ms": 2329,
  "completed_at": "..."
}
```

## 2b. Option B — SSE (push, no polling)

```bash
curl -N -H "Authorization: Bearer $VARG_SERVICE_KEY" \
     -H "Accept: text/event-stream" \
  https://render-fqb8zg.fly.dev/api/render/jobs/5f650644-fdba-47d5-b889-06b6be92826f/stream
```

Output (server pushes events, connection auto-closes after terminal):
```
event: status
data: {"job_id":"5f650644-...","status":"rendering"}

event: status
data: {"job_id":"5f650644-...","status":"completed","output_url":"https://s3.varg.ai/renders/xxx.mp4","files":[...],"duration_ms":2329}
```

## 3. Minimal JS client

```ts
async function renderVideo(code: string, apiKey: string): Promise<string> {
  const SERVICE_KEY = process.env.VARG_SERVICE_KEY!;

  // 1. Submit
  const res = await fetch("https://render-fqb8zg.fly.dev/api/render", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${SERVICE_KEY}`,
    },
    body: JSON.stringify({ code, gatewayApiKey: apiKey }),
  });
  const { job_id } = await res.json();

  // 2. Stream via SSE until done
  const sse = await fetch(
    `https://render-fqb8zg.fly.dev/api/render/jobs/${job_id}/stream`,
    { headers: { Authorization: `Bearer ${SERVICE_KEY}` } },
  );

  const reader = sse.body!.getReader();
  const decoder = new TextDecoder();
  let buf = "";

  while (true) {
    const { done, value } = await reader.read();
    if (done) break;
    buf += decoder.decode(value, { stream: true });
    for (const line of buf.split("\n")) {
      if (!line.startsWith("data: ")) continue;
      const event = JSON.parse(line.slice(6));
      if (event.status === "completed") return event.output_url;
      if (event.status === "failed") throw new Error(event.error);
    }
    buf = buf.slice(buf.lastIndexOf("\n") + 1);
  }

  throw new Error("Stream ended without terminal status");
}

// Usage
const url = await renderVideo(
  'export default <Render><Clip><Image prompt="a cat in space" /></Clip></Render>;',
  "varg_xxx",
);
console.log("Video:", url);
```