> Took them 3 months before a "we're not interested" email was sent. No reasons, either.

Yeh this is really really tough. They have an excellent RFD that explains the hiring process and it contains a section on this here: https://rfd.shared.oxide.computer/rfd/0003#_rejection_of_non...

I ported their Hubris kernel to RISC-V and ARMv6 before applying for a role to work on it, so thought I had reasonably strong materials, but got rejected.

I fully understand and empathise with their reasons for not providing feedback, but it does mean you're left not knowing whether you were a hair's breadth away from getting in but were behind a better candidate and it would be worth trying again in the future, or rejected for other reasons that no improvement in materials will make up for. As a fully signed-up member of imposter syndrome club I'll obviously lean towards the latter ;)