function install_to_custom_fonts( string $chat_id, string $filename, string $font_name = '' ) {
		if ( ! extension_loaded( 'fileinfo' ) ) {
			return new WP_Error(
				'fileinfo_extension_not_loaded',
				esc_html__( 'Font install requires the fileinfo PHP extension.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		if ( ! self::_validate_chat_id( $chat_id ) ) {
			return new WP_Error(
				'invalid_chat_id',
				esc_html__( 'Invalid chat identifier.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$ownership = self::assert_chat_ownership( $chat_id );

		if ( is_wp_error( $ownership ) ) {
			return $ownership;
		}

		if ( false !== strpos( $filename, '/' ) || false !== strpos( $filename, '\\' ) ) {
			return new WP_Error(
				'invalid_url',
				esc_html__( 'Could not parse chat ID and filename from URL.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$filename = sanitize_file_name( $filename );
		$base_dir = realpath( self::_get_base_dir() );

		if ( false === $base_dir || '' === $filename ) {
			return new WP_Error(
				'invalid_file',
				esc_html__( 'Invalid file reference.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$source_path = self::_get_base_dir() . '/' . $chat_id . '/' . $filename;
		$resolved    = realpath( $source_path );

		if ( false === $resolved || ! str_starts_with( $resolved, $base_dir ) || ! file_exists( $resolved ) ) {
			return new WP_Error(
				'file_not_found',
				esc_html__( 'Attachment file not found.', 'et_builder_5' ),
				[ 'status' => 404 ]
			);
		}

		$file_size = filesize( $resolved );

		if ( false === $file_size || self::MAX_FILE_SIZE < $file_size ) {
			return new WP_Error(
				'file_too_large',
				esc_html__( 'Font must be under 10MB.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$ext       = strtolower( pathinfo( $filename, PATHINFO_EXTENSION ) );
		$supported = self::_get_supported_font_formats();

		if ( '' === $ext || ! in_array( $ext, $supported, true ) ) {
			return new WP_Error(
				'invalid_font_format',
				esc_html__( 'This font format is not supported.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$checked = HooksRegistration::check_filetype_and_ext_font(
			[
				'ext'             => false,
				'type'            => false,
				'proper_filename' => false,
			],
			$resolved,
			$filename
		);

		if ( empty( $checked['ext'] ) || empty( $checked['type'] ) ) {
			return new WP_Error(
				'invalid_mime',
				esc_html__( 'Only supported font files can be installed as custom fonts.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		if ( ! in_array( strtolower( (string) $checked['ext'] ), $supported, true ) ) {
			return new WP_Error(
				'invalid_font_format',
				esc_html__( 'This font format is not supported.', 'et_builder_5' ),
				[ 'status' => 400 ]
			);
		}

		$temp = wp_tempnam( $filename );

		if ( false === $temp ) {
			return new WP_Error(
				'temp_file_error',
				esc_html__( 'Failed to prepare font file for install.', 'et_builder_5' ),
				[ 'status' => 500 ]
			);
		}

		if ( ! copy( $resolved, $temp ) ) {
			wp_delete_file( $temp );

			return new WP_Error(
				'copy_failed',
				esc_html__( 'Failed to prepare font file for install.', 'et_builder_5' ),
				[ 'status' => 500 ]
			);
		}

		$resolved_font_name = '' !== $font_name ? $font_name : pathinfo( $filename, PATHINFO_FILENAME );

		$result = FontsUtility::font_add(
			[
				$checked['ext'] => [
					'name'     => $filename,
					'type'     => $checked['type'],
					'tmp_name' => $temp,
					'error'    => 0,
					'size'     => filesize( $temp ),
				],
			],
			$resolved_font_name,
			[
				'font_weights'   => 'all',
				'generic_family' => 'sans-serif',
			],
			[
				'action' => 'wp_handle_upload_rest',
			]
		);

		if ( file_exists( $temp ) ) {
			wp_delete_file( $temp );
		}

		return $result;
	}