transferLeadership

Initiates a graceful leadership transfer to target per Raft §3.10, and suspends until the transfer either completes (target wins an election) or fails.

Protocol:

1. The leader stops accepting new propose calls (they receive NotLeaderException).

2. The leader sends AppendEntries to bring target's log up to the current commitIndex.

3. The leader sends a TimeoutNow message to target.

4. target immediately starts a real election (bypassing its election-timeout wait).

5. If target wins, the old leader steps down naturally on seeing the higher term. This call returns normally.

6. If target does not win within one election-timeout window, the auto-timeout fires: the old leader resumes accepting proposals and this call throws LeadershipTransferException.

Cancellation: call cancelTransfer from a separate coroutine to abort early. The LeadershipTransferException will carry "cancelled" in its message.

Constraints:

• Only the leader may call this. Non-leaders throw NotLeaderException immediately.

• target must be a voter in the current cluster config, and must not be this node's own id. Invalid targets throw IllegalArgumentException immediately.

• While a transfer is in flight, propose throws NotLeaderException.

Parameters

Throws