* master: never auto-admit raft peers on a single-node configuration
A master started without cluster peers (peers=none, or no peers so the
list holds only itself) declares a one-node cluster, yet any foreign
master that registered over KeepConnected was admitted as a second
voter. The resulting two-voter cluster cannot reach quorum when the
foreign peer is unreachable, wedging a previously healthy single
master. Gate raft admission on having been configured with cluster
peers; masters started with a peer list keep the announce-to-join
flow used to grow the cluster.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
* master: source SingleMaster from -peers=none, not the peer count
A master started with an empty peer list ends up with a one-peer map
containing itself, and NewMasterServer inferred declared single-master
mode from that count. The master still mints a raft cluster through the
bootstrap path, but AdmitRaftPeer then ignores every later joiner, so a
deployment that grows from one master to several can never form a
quorum. isSingleMasterMode already spells out the declared case
(-peers=none); populate MasterOption.SingleMaster from it instead.
* master: cover clustered raft admission with a real in-memory leader
The previous clustered test had no raft leader and asserted nothing, so
an AdmitRaftPeer that always returned early still passed. Bootstrap a
single-node hashicorp raft over the in-memory transport, wait for
leadership, and assert the leader reports and admits a missing peer.
* master: return the raft admission result and assert committed join
AdmitRaftPeer ran AddVoter on a detached goroutine, so the only observable
state was an in-flight marker deleted on success and failure alike, and the
clustered test could never tell whether the join worked. Admission now
hands back a result channel; the test runs a connected second in-memory
node and asserts the peer sees itself a committed voter.
---------
Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
