Once we have done our evaluation and are ready to do a port, we have to figure out what shape Parsoid-PHP will take
If we are going to create a new repository, we have to make sure to initialize it with the existing Parsoid git history
We have since resolved that this will be a composer library and will interface with MediaWiki core via T212982: Create a ParsingEnvironment class for use with Parsoid/PHP, T213228: Implement class (name to be decided) to provide access to preprocessor, extensions, and other metadata needed by Parsoid and one more MediaWiki core class (task yet to be created) that implements the REST API provided by Parsoid/JS.
Oh, that task already exists - T205339: Implement Parsoid's API / URL routing in MediaWiki core