5a62100397
Add HasQuorum() to RaftNode that counts peers with LastContact within 2 × ElectionTimeoutMaxMs and returns true only when self + current peers reaches majority. ProposeAsync now throws InvalidOperationException with "no quorum" when HasQuorum() returns false, preventing a partitioned leader from diverging the log. Add 14 tests in RaftQuorumCheckTests.cs covering single-node, 3-node, 5-node, boundary window, and heartbeat restore scenarios. Update RaftHealthTests.LastContact_updates_on_successful_replication to avoid triggering the new quorum guard.