Anybody good with Latin? I'm working my way through Einhard's Vita Karoli Magni, and I'm struggling with the bolded clause below:
Suberat et alia non inrationabilis, ut opinor, causa, quae uel sola sufficere posset ad haec scribenda conpelleret, nutrimentum uidelicet in me inpensum et perpetua, postquam in aula eius conuersari coepi, cum ipso ac liberis eius amicitia; qua me ita sibi deuinxit debitoremque tam uiuo quam mortuo constituit, ut merito ingratus uideri et iudicari possem, si ego tot beneficiorum in me conlatorum inmemor clarissima et inlustrissima hominis optime de me meriti gesta silentio praeterirem patererque uitam eius, quasi qui numquam uixerit, sine litteris ac debita laude manere; cui scribendae atque explicandae non meum ingeniolum, quod exile et paruum, immo poene nullum est, sed Tullianam par erat desudare facundiam.
I get the gist of what the clause is saying; that composing [this biography] is so difficult that it would stretch not only his own (Einhard's) capacities for eloquence (which are indeed slim and scarcely existent) but would even cause someone on the level of Tullius (Cicero) to sweat.
What I'm struggling to understand is why the subjects of the relative clause (introduced by cui), namely "meum ingeniolum" and "Tullianam facundiam" are in the accusative. As far as I can tell it's not indirect speech. Although the forms being subject accusatives would explain it, and indeed would also point to why desudo is in its infinitive form, I don't see a clause or verb introducing the indirect speech.
Beyond that, They aren't objects of the gerundives (scribendae/explicandae). They aren't future passive conjugations; for that est and erat would have to be sunt and erant, respectively. Dative of possession constructions don't take the accusative. There is no accusative agent (I think?). I don't see what it could be.