RunClaim

A run's lease on a thread, as a Checkpointer granted it: the run that holds it, the FencingToken its commits must carry, and when it expires by the store's clock unless renewed. While it is live - expiresAt has not passed - no other claim on the thread is granted, so a run in another runtime or process is refused with GraphError.ThreadBusy. Once it has expired, another run may take the thread over, and the store then refuses this claim's token (GraphError.StaleClaim). Until then the holder may still commit and renew, even past expiresAt: expiry only lets another run claim the thread.