It looks like v0.19.0 support will keep photon compatible with v0.18.0. I just need to send both query parameter and a header, so that v0.19.0 will accept the header and v0.18.0 will accept the parameter. I thought v0.19.0 would deny the query parameter, returning an error. Thankfully, the Lemmy devs were sane.
Well let’s just say mistakes and missteps are the path to success