Are block templates incompatible with serialize_blocks?

Question

I need to dynamically create posts from arbitrary content using wp_insert_post() and wp_update_post(). The post type I'm working with has a simple block template associated with it, so my goal is to get the block template attached to the post type object, insert my post content into the template using innerContent, and then use serialize_blocks to turn the template into renderable post_content markup (e.g. with markup).

My problem is that block templates are defined in PHP as indexed arrays:

$post_object->template = array(
   array( 'core/image', array(
        'align' => 'left',
   ) ),
   array( 'core/heading', array(
        'placeholder' => 'Add Author...',
   ) ),
   array( 'core/paragraph', array(
        'placeholder' => 'Add Description...',
    ) ),
);

While serialize_blocks() appears to require associative arrays similar to what parse_blocks returns:

$blocks = parse_blocks( $post->post_content );
var_dump( $blocks );
// array(
//   array( 'blockName' => 'core/image', 'attrs' => array(
//      'align' => 'left',
// ) ),
//  array( 'blockName' => 'core/heading', 'attrs' => array(
//       'placeholder' => 'Add Author...',
// ) ),
// array( 'blockName' => 'core/paragraph', 'attrs' => array(
//      'placeholder' => 'Add Description...',
//  ) ),
//);

Attempting to define a block template as an associative array breaks the editor, and attempting to serialize blocks using an indexed array results in undefined index and invalid argument warnings from wp-includes/blocks.php with nothing being returned by the function.

Is there something I'm missing here? Some other intermediary function to transpose an indexed block template array into the associative array format that parse_blocks returns?

Answer 1

This comment on another post sent me off in the right direction for a solution that converts the indexed array of a block template to an associative array that resembles the output of parse_blocks (below).

But the larger question still remains: why would block templates not follow the same structure and format that parse_blocks uses? Are they not meant to be used in similar ways? Is there some other native solution for converting a block template into renderable post content or even rendered html?

Here's a stop gap solution that converts the indexed array of a block template into the associative array that serialize_blocks requires:

function block_template_to_associative_array( $blocks ){
    $blocks_array = [];
    foreach( $blocks as $block ):
        $blocks_array[] = [
            'blockName' => $block[0],
            'attrs' => $block[1] ?? [],
            'innerBlocks' => isset( $block[2] ) ? block_template_to_associative_array( $block[2] ) : [],
            'innerHTML' => $block[3] ?? [],
            'innerContent' => $block[4] ?? []
        ];
    endforeach;
    return $blocks_array;
}

Edit: unfortunately this is only a partial solution. It results in something close to what parse_blocks creates from post_content, but lacking the innerHTML and innerContent necessary to properly render in the editor. Using serialize_blocks and then inserting into post_content results in "This block contains unexpected or invalid content" errors, but attempting Block Recovery successfully restores all blocks and inner blocks.