It was a crude hack that this one low-level function was dependent on
the high-level read-only mode setting --- all the more so because rather
than making derivation writing fail, that setting made it silently
"succeed" why not actually writing the derivation. (Also, for context,
we didn't have an such behavior for any other store-mutating operations,
just for this one function.)
I have gotten rid of the wrapper, and updated the call sites
accordingly.
- For the ones that should remain dependent on this setting, I made this
explicit, and added a comment.
- For others, surrounding operations assumed writability (e.g. we had
written something before, or were about to try to read back the
written derivation after), and so I just made those do the underlying
`Store::writeDerivation` operation.
7926a629e2