Adding or replacing image size

It seems that this regex does the trick:

wp search-replace '(<!-- wp:image\s{(?!.*"sizeSlug")[^}]*)' '$1,\"sizeSlug\":\"full\"' wp_posts --regex --regex-delimiter="https://wordpress.stackexchange.com/" --precise

EDIT:
I added correction, double quotes must be escaped in replacement string in order for this to work properly. It seems that everything is first encoded in json, hence the reason.

ANOTHER EDIT:
This did the trick by updating post content by adding attribute, but srcset and sizes are still missing.

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