The Vercel connector reads the team from the camelCase teamId callback
parameter, unlike the snake_case params most providers use. Nothing
guarded the name, so a regression back to team_id would silently drop
the team on every Vercel connect and leave the source resolving no
users.
Extract the read into vercelCallbackTeamID and pin the exact parameter
name with a test, since the surrounding handler needs a live connector
registry and database to exercise directly.
Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>
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