Push state to the backing Gist when Gist mode is active. Best-effort:
network/auth failures are logged via warn() but never propagated —
the caller's primary mutation has already succeeded locally and the
next successful push (or a daily run) will re-sync.
Intended for state-mutating PR-flow commands (shelve / unshelve / move /
dismiss / undismiss / claim) so Gist-sync users don't see day-long drift
between machines waiting for the next daily checkpoint. See issue #1036.
null when the push succeeded (or Gist mode is off); otherwise a
human-readable warning the caller should surface in its structured output.
checkpoint() resolves false without throwing when the push failed
after its retry — previously that was discarded everywhere except
state --sync, so a failed cross-machine sync reported clean success
(#1370). stderr warn() alone is invisible to MCP/dashboard consumers.
Core module exports Re-exports all core functionality for convenient imports