docs: "## Checkpoint Sync\n\nIncremental sync using checkpoint-based change tracking.\n\n**Method:** POST\n\n**Endpoint:** /api/sync/koreader/progress\n\n**Authentication:** Bearer token\n\n**Request Body:**\n- `sync_mode` (string): Must be `checkpoint`\n- `checkpoint_id` (string): Unique checkpoint identifier\n- `since_timestamp` (string): ISO 8601 timestamp for incremental sync\n- `books` (array): Book progress items\n  - `uuid` (string): Book UUID\n  - `percentage` (number): Progress 0.0-1.0\n  - `chapter` (integer): Current chapter\n  - `epubcfi` (string, optional): Current position\n  - `modified_since` (boolean, optional): Whether modified since checkpoint\n\n**Response:**\n- `checkpoint_id` (string): Server checkpoint ID\n- `checkpoint_timestamp` (string): Checkpoint creation time\n- `processed` (integer): Books processed\n- `changes_only` (boolean): Whether only changed items synced\n- `next_checkpoint_id` (string): ID for next checkpoint sync\n- `results` (array): Per-book results\n\
  \n**Status Codes:**\n- 200: Checkpoint sync completed\n- 401: Unauthorized\n- 400: Invalid checkpoint or timestamp\n\n**Checkpoint Sync Benefits:**\n- **Incremental**: Only sync changed items\n- **Efficient**: Smaller payloads\n- **Fast**: Reduced processing time\n- **Reliable**: Checkpoint-based tracking\n- **Resumable**: Can continue from last checkpoint\n\n**Checkpoint Mechanism:**\n- Server tracks changes since checkpoint\n- Client provides checkpoint ID or timestamp\n- Only modified books returned/processed\n- Checkpoint ID advances on each sync\n- Supports large libraries efficiently\n\n**Use Cases:**\n- Large libraries (100+ books)\n- Intermittent connectivity\n- Bandwidth optimization\n- Battery conservation\n- Background sync\n- Periodic sync (every 5-15 minutes)\n\n**Checkpoint Lifecycle:**\n1. Initial sync: No checkpoint (full sync)\n2. Server returns checkpoint_id\n3. Next sync: Client sends checkpoint_id\n4. Server processes only changes\n5. New checkpoint_id returned\n6.\
  \ Repeat from step 3\n\n**Sync Optimization:**\n- Only books with progress changes\n- Skips unmodified books\n- Delta transfer\n- Compression for large payloads\n- Batch processing\n\n**Failure Handling:**\n- Checkpoint ID preserved on failure\n- Retry with same checkpoint\n- Full sync if checkpoint expired\n- Checkpoint validity: 24 hours\n- Auto-fallback to full sync\n\n**Performance:**\n- Small changes (1-10 books): 100-300ms\n- Medium changes (10-50 books): 300ms-1s\n- Large changes (50-100 books): 1-3s\n- Typical: 5-10x faster than full sync\n\n**When to Use:**\n- Default sync mode for most users\n- Periodic background sync\n- Large library management\n- Mobile/network-constrained environments\n- Battery-powered devices\n\n**Configuration:**\n- Checkpoint expiration: 24 hours\n- Max history: 100 checkpoints\n- Auto-cleanup of old checkpoints\n- Configurable sync interval"
http:
  body:
    type: json
    data: "{\n  \"books\": [\n    {\n      \"chapter\": 3,\n      \"percentage\": 0.45,\n      \"uuid\": \"{{media_item_id}}\"\n    },\n    {\n      \"chapter\": 8,\n      \"percentage\": 0.75,\n      \"uuid\": \"{{media_item_id}}\"\n    }\n  ],\n  \"checkpoint_id\": \"checkpoint-uuid\",\n  \"since_timestamp\": \"2026-01-30T19:00:00Z\",\n  \"sync_mode\": \"checkpoint\"\n}"
  headers:
  - key: Content-Type
    value: application/json
  method: POST
  url: '{{base_url}}/api/sync/koreader/progress'
  auth:
    type: bearer
    token: '{{koreader_device_token}}'
info:
  name: Checkpoint Sync
  seq: 11
  type: http