The "solid agreement" still stands - the 2007 arrangements are clear that the contributions are made up of the SCR (standard contribution rate) plus an actuarially calculated supplement. So potential increases are part of the existing scheme. And sustainability is not immutable - it has been in deficit in recent years and with increasing longevity will be so again.
Raising the retirement age, which is hitting the entire workforce, is an issue though, as I do not see why the normal retirement age is increasing by more than that required of other workers (for teachers it appears to be 68, not 66). But perhaps this is foreshadowing 68 for all of us?