A server without thread PR snapshots only reports the legacy linked PR,
which clients turn into a link with no snapshot. The Git status fallback
treated that as open forever, so a merged legacy PR kept replacing the
checkout's status and suppressed Create PR. Unsynced links now count as
open only when the server advertises threadPullRequests; links with an
explicit open snapshot still stand in regardless.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>