Capacitors, charge and energy: a question

[Kalee20]

Resistor? What resistor?
In my initial post, where I outlined the hypothetical ideal situation and the associated fundamental equations applicable to that situation, all resistances were zero.

Yes - you can calculate the loss (if you want) in a resistor connecting the two capacitors, from the moment of connecting them together, to t = infinity, by integration. The integrand is a function of R but it turns out that R disappears from the final integral result, which depends only on capacitance values and initial voltages.

Then you let R tend to zero - you've got the case you postulated, and there's still 25µJ lost!