A source checkout on the main channel failed every update check with
"Could not resolve the main source channel: Channel object not found:
releases/channels/main.json" until R2 publishes that record, in the CLI
and in Desktop (which asks hermes_cli.source_check). main IS the source
branch -- its record can only add a retirement -- so a missing main record
now resolves to the main branch and the update continues via git. Other
channels, and transient read failures for main, still refuse.
1dd9a9955d