Return entity reference fields recursively as full-fledged entity objects

Currently, entity's referred to be entityreference fields are stubs of an entry including only the referred entity's:

• ID;
• resource type (i.e. node, user, etc.); and
• fully-qualified resource canonical URI (i.e. http://example.com/en/node/10).

For graphs of entities connected by entityreference, multiple rounds of GET requests are needed to fully traverse this graph/network/bunch-of-entities. I'd like to be able to recursively load the tree of connected entities in a single request.

The related issue I've quoted here does this using what appears to an obsolete hook_restws_response_alter() and it's not trivial to port it to the current hook as it stands.

The former code snippet assumes the $response is an array expression that includes the entity's fields as keyed elements. The current hook_restws_response_alter() receives $response as a PHP DOMDocument class -- totally different kind of thing.

Edge cases include monkey wrenchs like cyclic networks. I'm going to assume, for now, that those don't exist / kittens will die if the first draft code snippet encounters a loop. I don't think the related issue I've referenced dealt with cyclic networks either.

I'll be working to close this gap, but any help would be appreciated. I'm also documenting it here for posterity.