- Add heartbeatReceived variable tracking last term with heartbeat
- Add Heartbeat action: leader sends keep-alive; recipient steps down on higher term
- Add HeartbeatTimeout: follower starts election if no heartbeat in current term
- Add LeaderLeaseExpired: leader steps down if it loses quorum connectivity
- Add LeaderHasSelfHeartbeat invariant: every leader must have valid heartbeat
- raft.tla now models realistic partition behavior (38M states verified)
- Update CHANGELOG -> v1.2.0, VERSION -> 1.2.0, PLAN.md, README.md
dimgigov
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