I'm honestly not sure where exactly to add the checks. We could modify connect, pass the elf data to that and check where we check the -c argument, but it feels out of scope for connect. On the other hand, now we have to add a check to every place it matters, so the PR is messier than it should be. Ideas?

I think I agree that it's a bit much for connect, but we already have flasher.verify_minimum_revision(), maybe a function on Flasher might make sense here. It might also avoid the Option<&[u8]> for elf data, as we can move that option check outside so that we only call flasher.verify_elf_compat() when there is elf data to verify against?

If you don't like that idea, I also think what you currently have isn't so bad, it's just three checks.

I've grouped the two bits of metadata into Metadata. Ideally, I think espflash should have a single Image struct that is parsed once, then used to extract metadata & symbols, but that's a bigger refactor than I'd like. Perf-wise we read all symbols twice because we extract Metadata twice, as opposed to looking up two symbols using linear search, so in the worst case we are in the same place.