feat(cluster): add Agent.Leader() accessor#160
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External monitoring tools and the dashboard's cluster topology view need to know which node currently holds the Raft leadership. raftPeer.GetLeader() exists but raftPeer is unexported, so the only way to read leader state today is to reach into unexported fields. Adds a trivial wrapper that returns the leader node id, or "" when no leader is elected. No behavior change inside the cluster runtime; this is a read-only accessor over state the package already tracks.
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Summary
Adds a small read-only accessor to
*cluster.Agent:Rationale
External monitoring tools and observability dashboards need to render which cluster node currently holds the Raft leadership. The information is already tracked by
a.raftPeer.GetLeader(), butraftPeeris unexported, so there is no in-tree way for callers outside theclusterpackage to read leader state without unsafe access to unexported fields.The accessor follows the same pattern as the
Server.Hooks()accessor merged in #158: a small wrapper that exposes existing state to observers, with no behavior change inside the package.Scope
""when no leader is elected (mid-election, pre-bootstrap), which is the sentinelraftPeer.GetLeader()already returns in those cases.Context
Needed by the
debsahu/comqtt-dashboardadd-on, which renders cluster topology and a leader badge on its Cluster page. The add-on was split out of #151 per maintainer feedback that the original PR was too large to evaluate; it now lives as a separate Go module so comqtt itself stays focused on the broker. This accessor is the only upstream change the dashboard's cluster-mode binary needs beyond #158.