Integrate Batch

Write Python functions to submit and retrieve results from the ScaleDown Batch API.

API details:

Submit batch — POST https://api.scaledown.xyz/v1/batches
- Auth: HTTP header `x-api-key: <your key>`
- Content-Type: application/jsonl
- Body: newline-delimited JSON (JSONL), one item per line. Each line:
    {
      "custom_id": "<string you assign>",
      "method": "POST",
      "url": "/v1/chat/completions",
      "body": {
        "model": "summarize" | "extract" | "classify",
        // model-specific fields below
      }
    }

  model="summarize" body fields:
    { "text": "<text>", "instructions": "<optional>", "max_tokens": 20048 }

  model="extract" body fields:
    {
      "text": "<text>",
      "entities": { "<label>": "<description>", ... },
      "instruction": "<optional>"
    }

  model="classify" body fields:
    {
      "text": "<text>",
      "labels": [{ "name": "<label>", "rubric": "<yes/no question>" }],
      "system_prompt": "<optional>"
    }

- Success response (JSON):
    { "batch_id": "<id>", "status": "queued", "total_count": <n> }

Poll status — GET https://api.scaledown.xyz/v1/batches/{batch_id}
- Returns: { "batch_id": "...", "status": "queued|processing|completed|failed", ... }
- Poll until status is "completed" or "failed"

Get output — GET https://api.scaledown.xyz/v1/batches/{batch_id}/output
- Returns JSONL. Each line:
    {
      "custom_id": "<your id>",
      "response": {
        "status_code": 200,
        "body": {
          "model": "summarize" | "extract" | "classify",
          "choices": [{ "message": { "content": "<JSON string>" } }]
        }
      },
      "error": null
    }
  Parse choices[0].message.content as JSON to get the domain result:
    summarize → { "summary": "...", "input_chars": n, "output_chars": n }
    extract   → { "entities": [{ "type": "...", "text": "...", "confidence": 0.99 }] }
    classify  → { "top_label": "...", "scores": { "<label>": float }, "reasoning": "..." }

Requirements:
- Implement submit_batch(items: list[dict], api_key: str) -> str that sends the JSONL
  and returns the batch_id.
- Implement poll_until_done(batch_id: str, api_key: str, interval: int = 5) -> dict
  that polls every `interval` seconds until status is "completed" or "failed",
  then returns the final status dict.
- Implement get_results(batch_id: str, api_key: str) -> list[dict] that fetches output
  and returns a list of parsed result dicts, each with keys: custom_id, model, content, error.
- Raise a ValueError with status code and body on any non-2xx response.

Write a production-quality Python module for integrating the ScaleDown Batch API.

API details:

Submit batch — POST https://api.scaledown.xyz/v1/batches
- Auth: HTTP header `x-api-key: <your key>`
- Content-Type: application/jsonl
- Body: newline-delimited JSON. Each line is a BatchItem:
    {
      "custom_id": "<string>",
      "method": "POST",
      "url": "/v1/chat/completions",
      "body": { "model": "summarize"|"extract"|"classify", ...model fields... }
    }

  model="summarize" → body fields: text (str), instructions (str, optional), max_tokens (int, default 20048)
  model="extract"   → body fields: text (str), entities (dict[str, str]), instruction (str, optional)
  model="classify"  → body fields: text (str), labels (list[{"name": str, "rubric": str}]), system_prompt (str, optional)

- Response: { "batch_id": str, "status": "queued", "total_count": int }

Poll — GET https://api.scaledown.xyz/v1/batches/{batch_id}
- Response: { "batch_id": str, "status": "queued"|"processing"|"completed"|"failed", ... }

Output — GET https://api.scaledown.xyz/v1/batches/{batch_id}/output
- Response: JSONL. Each line:
    {
      "custom_id": str,
      "response": {
        "status_code": int,
        "body": { "model": str, "choices": [{ "message": { "content": "<JSON string>" } }] }
      },
      "error": { "code": str, "message": str } | null
    }
  Deserialize choices[0].message.content as JSON:
    summarize → { "summary": str, "input_chars": int, "output_chars": int }
    extract   → { "entities": [{ "type": str, "text": str, "confidence": float, "start": int, "end": int }] }
    classify  → { "top_label": str, "scores": dict[str, float], "reasoning": str, "labels": list[dict] }

Apply these programming principles:

1. Environment configuration — Load the API key from SCALEDOWN_API_KEY. Raise a clear
   ValueError at construction time if it is missing.

2. Typed inputs — Define dataclasses:
     SummarizeItem(custom_id: str, text: str, instructions: str | None, max_tokens: int)
     ExtractItem(custom_id: str, text: str, entities: dict[str, str], instruction: str | None)
     ClassifyItem(custom_id: str, text: str, labels: list[dict], system_prompt: str | None)
   Define a union type: BatchInputItem = SummarizeItem | ExtractItem | ClassifyItem

3. Typed results — Define dataclasses:
     BatchItemResult(custom_id: str, model: str, content: dict, error: dict | None)
     BatchResult(batch_id: str, items: list[BatchItemResult])

4. Custom exception — ScaleDownBatchError(status_code: int, message: str).

5. Client class — ScaleDownBatchClient with methods:
     submit(items: list[BatchInputItem]) -> str  (returns batch_id)
     wait(batch_id: str, poll_interval: float = 5.0) -> dict  (polls until done, returns status dict)
     results(batch_id: str) -> BatchResult  (fetches and parses output JSONL)
     run(items: list[BatchInputItem], poll_interval: float = 5.0) -> BatchResult
       (submit + wait + results in one call)

6. Retry with exponential backoff — On HTTP 5xx from submit or output fetch, retry up to
   3 times with delays 2s, 4s, 8s. Raise ScaleDownBatchError after exhausting retries.

7. Type annotations — Full type annotations on all methods and fields.

Write an async Python module that submits a ScaleDown batch, polls for completion,
and fans out each completed item to a model-specific callback.

ScaleDown Batch API:
- Submit: POST https://api.scaledown.xyz/v1/batches
  Headers: x-api-key, content-type: application/jsonl
  Body: JSONL with one item per line:
    { "custom_id": str, "method": "POST", "url": "/v1/chat/completions",
      "body": { "model": "summarize"|"extract"|"classify", ...fields... } }
  Response: { "batch_id": str, "status": "queued", "total_count": int }

- Poll:   GET https://api.scaledown.xyz/v1/batches/{batch_id}
  Response: { "status": "queued"|"processing"|"completed"|"failed", ... }

- Output: GET https://api.scaledown.xyz/v1/batches/{batch_id}/output
  Response: JSONL. Each line: { "custom_id": str, "response": { "body": { "model": str,
    "choices": [{ "message": { "content": "<JSON string>" } }] } }, "error": null|{...} }
  Parse choices[0].message.content as JSON for the domain result.

Requirements:

1. Accept a list of batch item dicts and a dict of callbacks:
     callbacks: dict[str, Callable[[str, dict], Awaitable[None]]]
   Keys are "summarize", "extract", "classify". Each callback receives (custom_id, content_dict).

2. Implement async run_batch(items, callbacks, api_key, poll_interval=5.0) using httpx.AsyncClient.
   - POST the JSONL to submit the batch.
   - Poll every poll_interval seconds using asyncio.sleep until status is "completed" or "failed".
   - If status is "failed", raise a RuntimeError with the batch_id.
   - Fetch output JSONL and for each line: parse content, look up the callback by model,
     and await it with (custom_id, content_dict). Skip items where error is not null.

3. Run all callbacks concurrently using asyncio.gather once output is fetched.

4. Add a __main__ block demonstrating the API with one summarize, one extract, and one classify item,
   printing the custom_id and a short preview of the result in each callback.