feat: Implement rehydration and purge functionality for deltaglider files

- Added `rehydrate_for_download` method to download and decompress deltaglider-compressed files, re-uploading them with expiration metadata.
- Introduced `generate_presigned_url_with_rehydration` method to generate presigned URLs that automatically handle rehydration for both regular and deltaglider files.
- Implemented `purge_temp_files` command in CLI to delete expired temporary files from the .deltaglider/tmp/ directory, with options for dry run and JSON output.
- Enhanced service methods to support the new rehydration and purging features, including detailed logging and metrics tracking.

src/deltaglider/client.py

@@ -1220,6 +1220,125 @@ class DeltaGliderClient:
         self._invalidate_bucket_stats_cache()
         self.service.cache.clear()
 
+    def rehydrate_for_download(
+        self, 
+        Bucket: str, 
+        Key: str, 
+        ExpiresIn: int = 3600
+    ) -> str | None:
+        """Rehydrate a deltaglider-compressed file for direct download.
+        
+        If the file is deltaglider-compressed, this will:
+        1. Download and decompress the file
+        2. Re-upload to .deltaglider/tmp/ with expiration metadata
+        3. Return the new temporary file key
+        
+        If the file is not deltaglider-compressed, returns None.
+        
+        Args:
+            Bucket: S3 bucket name
+            Key: Object key
+            ExpiresIn: How long the temporary file should exist (seconds)
+            
+        Returns:
+            New key for temporary file, or None if not deltaglider-compressed
+            
+        Example:
+            >>> client = create_client()
+            >>> temp_key = client.rehydrate_for_download(
+            ...     Bucket='my-bucket',
+            ...     Key='large-file.zip.delta',
+            ...     ExpiresIn=3600  # 1 hour
+            ... )
+            >>> if temp_key:
+            ...     # Generate presigned URL for the temporary file
+            ...     url = client.generate_presigned_url(
+            ...         'get_object',
+            ...         Params={'Bucket': 'my-bucket', 'Key': temp_key},
+            ...         ExpiresIn=3600
+            ...     )
+        """
+        return self.service.rehydrate_for_download(Bucket, Key, ExpiresIn)
+
+    def generate_presigned_url_with_rehydration(
+        self,
+        Bucket: str,
+        Key: str,
+        ExpiresIn: int = 3600,
+    ) -> str:
+        """Generate a presigned URL with automatic rehydration for deltaglider files.
+        
+        This method handles both regular and deltaglider-compressed files:
+        - For regular files: Returns a standard presigned URL
+        - For deltaglider files: Rehydrates to temporary location and returns presigned URL
+        
+        Args:
+            Bucket: S3 bucket name
+            Key: Object key
+            ExpiresIn: URL expiration time in seconds
+            
+        Returns:
+            Presigned URL for direct download
+            
+        Example:
+            >>> client = create_client()
+            >>> # Works for both regular and deltaglider files
+            >>> url = client.generate_presigned_url_with_rehydration(
+            ...     Bucket='my-bucket',
+            ...     Key='any-file.zip',  # or 'any-file.zip.delta'
+            ...     ExpiresIn=3600
+            ... )
+            >>> print(f"Download URL: {url}")
+        """
+        # Try to rehydrate if it's a deltaglider file
+        temp_key = self.rehydrate_for_download(Bucket, Key, ExpiresIn)
+        
+        # Use the temporary key if rehydration occurred, otherwise use original
+        download_key = temp_key if temp_key else Key
+        
+        # Extract the original filename for Content-Disposition header
+        original_filename = Key.removesuffix(".delta") if Key.endswith(".delta") else Key
+        if "/" in original_filename:
+            original_filename = original_filename.split("/")[-1]
+        
+        # Generate presigned URL with Content-Disposition to force correct filename
+        params = {'Bucket': Bucket, 'Key': download_key}
+        if temp_key:
+            # For rehydrated files, set Content-Disposition to use original filename
+            params['ResponseContentDisposition'] = f'attachment; filename="{original_filename}"'
+        
+        return self.generate_presigned_url(
+            'get_object',
+            Params=params,
+            ExpiresIn=ExpiresIn
+        )
+
+    def purge_temp_files(self, Bucket: str) -> dict[str, Any]:
+        """Purge expired temporary files from .deltaglider/tmp/.
+        
+        Scans the .deltaglider/tmp/ prefix and deletes any files
+        whose dg-expires-at metadata indicates they have expired.
+        
+        Args:
+            Bucket: S3 bucket to purge temp files from
+            
+        Returns:
+            dict with purge statistics including:
+            - deleted_count: Number of files deleted
+            - expired_count: Number of expired files found
+            - error_count: Number of errors encountered
+            - total_size_freed: Total bytes freed
+            - duration_seconds: Operation duration
+            - errors: List of error messages
+            
+        Example:
+            >>> client = create_client()
+            >>> result = client.purge_temp_files(Bucket='my-bucket')
+            >>> print(f"Deleted {result['deleted_count']} expired files")
+            >>> print(f"Freed {result['total_size_freed']} bytes")
+        """
+        return self.service.purge_temp_files(Bucket)
+
 
 def create_client(
     endpoint_url: str | None = None,