Wikibase assembles the outgoing links from an entity page via the EntityReferenceExtractor, called by the ReferencedEntitiesDataUpdater. Since we’re using the string data value type instead of the entity ID data value type, I think we need to add a hook to StatementEntityReferenceExtractor::processSnak() or somewhere in the vicinity. (processDataValue() in its current form isn’t enough: by that point, we don’t know which property data type the data value belonged to, i.e. whether a StringValue('E10') is an EntitySchema reference or some unrelated string.)

Mh, there is \Wikibase\Repo\ParserOutput\EntityParserOutputDataUpdaterCollection, which looks like we could in principle add an EntitySchemaParserOutputDataUpdater to it.

Though going a bit up the call stack, it seems Wikibase has custom code for associated extensions to add their updaters in \Wikibase\Repo\ParserOutput\EntityParserOutputGeneratorFactory::getDataUpdaters

	private function getDataUpdaters(): array {

		// [...]

		if ( ExtensionRegistry::getInstance()->isLoaded( 'GeoData' ) ) {
			$statementUpdater->addUpdater( $this->newGeoDataDataUpdater( $propertyDataTypeMatcher ) );
		}

		if ( ExtensionRegistry::getInstance()->isLoaded( 'Math' ) ) {
			$statementUpdater->addUpdater( new MathDataUpdater( $propertyDataTypeMatcher ) );

		}

		// FIXME: null implementation of KartographerEmbeddingHandler would seem better than null pointer
		// in general, and would also remove the need for the check here
		if ( $this->kartographerEmbeddingHandler ) {
			$statementUpdater->addUpdater( $this->newKartographerDataUpdater() );
		}

		// [...]

		// TODO: do not use global state
		Hooks::run(
			'WikibaseRepoOnParserOutputUpdaterConstruction',
			[
				$statementUpdater,
				&$entityUpdaters,
			]
		);

		return $entityUpdaters;
	}

And there is also a hook that looks like we could use it? Though in general this method has a lot of // TODO and // FIXME to it, that maybe we want to use this opportunity to spend a bit of time on thinking about how we can improve it.

That WikibaseRepoOnParserOutputUpdaterConstruction hook is apparently what Lexeme is using (see codesearch to add LexemeParserOutputUpdater to the stack.

Change 909691 had a related patch set uploaded (by Hoo man; author: Hoo man):

[mediawiki/extensions/EntitySchema@master] Add statement links to EntitySchema "What links here"

https://gerrit.wikimedia.org/r/909691

Change 909691 merged by jenkins-bot:

[mediawiki/extensions/EntitySchema@master] Add statement links to EntitySchema "What links here"

https://gerrit.wikimedia.org/r/909691

Can be verified on beta: https://wikidata.beta.wmflabs.org/wiki/Special:WhatLinksHere/EntitySchema:E12