# `PUT /category/order`

Protected. Requires a valid session cookie (`credentials: 'include'`).

Reorder sibling categories

Sets the sibling sort order of `categoryIds` under `parentId`.
`categoryIds` must be exactly the current child set of `parentId`
(same count, no foreign/duplicate ids). Each child's `sort` is set
to its index `0..n-1` in one transaction.


## Body (JSON)

| Field | Required | Type | Description |
|-------|----------|------|-------------|
| `parentId` | yes | integer | Parent category under which sibling order applies |
| `categoryIds` | yes | integer[] |  |

```json
{
  "parentId": 1,
  "categoryIds": [
    2,
    4,
    3,
    5
  ]
}
```

## Signals

On success, emits SSE signal: `category` (see [`GET /events`](../events.md)).

## Response `200`

New sibling order

```json
{
  "categoryIds": [
    1
  ]
}
```

## Errors

| Status | Description |
|--------|-------------|
| 400 | Invalid category order — `{"error":"…"}` |
| 401 | Unauthorized — `{"error":"…"}` |
| 403 | Not authorized — `{"error":"…"}` |
| 404 | Parent category not found — `{"error":"…"}` |

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