Module lifecycle 

Node lifecycle management: join, leave, decommission.

Handles the full lifecycle of a node in the cluster:

1. Join: Node contacts seed, receives topology, joins as Learner, catches up Raft logs, promoted to Active voter.
2. Decommission: Node drains leadership, migrates all vShards to other nodes, then shuts down cleanly.
3. Leave: Node is removed from topology after decommission completes.

All transitions are replicated via the metadata Raft group to ensure consistency across the cluster.

Structs

DecommissionResult

Result of a decommission operation.

Functions

handle_learner_promotion

Handle learner promotion after state catch-up validation.

handle_node_join

Apply a topology change: handle join, leave, or state transition.

is_safe_to_remove

Check if a node can be safely removed from the cluster.

plan_decommission

Plan a node decommission: compute which vShards to migrate and where.