In OfflineMasterKey mode master keys are not supposed to be available, do not suggest they should be
When Ed25519 signing keys expire tor logs the following messages:
(1) [notice] It looks like I should try to generate and sign a new medium-term signing key, because the one I have is going to expire soon. But OfflineMasterKey is set, so I won't try to load a permanent master identity key is set. You will need to use 'tor --keygen' make a new signing key and certificate. (2) [notice] It looks like I need to generate and sign a new medium-term signing key, because the one I have is expired. To do that, I need to load the permanent master identity key. (3)[warn] We needed to load a secret key from .../tor/keys/ed25519_master_id_secret_key, but couldn't find it. Did you forget to copy it over when you copied the rest of the signing key material? (4)[warn] Can't load master identity key; OfflineMasterKey is set. (5)[err] Unable to update Ed25519 keys! Exiting.
(3) suggests that one forgot to copy the master key, but in such a setup OfflineMasterKey 1, the masterkey is not supposed to be there, so the warn message could be replaced with "please provide tor with new valid Ed25519 signing keys/cert" (or similar) instead of suggesting to the user that it should copy the master key to the relay - which is not recommended, no?