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 as MetadataEntry::TopologyChange / MetadataEntry::RoutingChange entries and applied through the MetadataApplier on every node.

Structs

DecommissionResult

Result of a decommission operation.

Functions

handle_learner_promotion

Handle learner promotion after state catch-up validation.

handle_node_join

Register a joining node in the local topology and produce the MetadataEntry to be proposed on the metadata Raft group.

is_safe_to_remove

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

plan_decommission

Plan a node decommission — thin wrapper over crate::decommission::plan_full_decommission that returns the full ordered sequence of metadata entries. Kept as a public convenience for older call sites; new code should use the decommission module directly.