A source checkout without hermes_cli/source_check.py predates release
channels, so the only line it can be on is git. The desktop treated the
missing probe as unsupported and parked the user on a manual
`hermes update --help` card ("This checkout predates desktop
source-channel checks"), so an older non-bundled install could never
update itself from the app.
Report such a checkout as tracking main with an update available and let
apply take the normal git handoff. That update brings in the probe, so
later checks resolve normally. A probe that exists but fails still throws.
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