The zids parameter of the wikilambda_fetch API action takes multiple ZIDs, but doesn’t properly declare this in the API parameters; it’s only explained in prose in the parameter documentation, and then the execute() method manually explode()s the param value.

It should declare the parameter as PARAM_ISMULTI, so that e.g. the API sandbox properly supports working with multiple values, as it does for other parameters:

With this, MediaWiki will not only split the value for you, it’ll also apply limits so that users don’t request thousands of objects at once.