* fix(master): skip redundant DoJoinCommand on resumeState to prevent deadlock
When fastResume is active (single-master + resumeState + non-empty log),
the raft server becomes leader within ~1ms. DoJoinCommand then enters
the leaderLoop's processCommand path, which calls setCommitIndex to
commit all pending entries. The goraft setCommitIndex implementation
returns early when it encounters a JoinCommand entry (to recalculate
quorum), which can prevent the new entry's event channel from being
notified — leaving DoJoinCommand blocked forever.
Each restart appends a new raft:join entry to the log, while the conf
file's commitIndex (only persisted on AddPeer) lags behind. After 3-4
restarts the uncommitted range contains old JoinCommand entries that
trigger the early return before the new entry is reached.
Fix: skip DoJoinCommand when the raft log already has entries (the
server was already joined in a previous run). The fastResume mechanism
handles leader election independently.
* fix(master): handle Hashicorp Raft in HasExistingState
Add Hashicorp Raft support to HasExistingState by checking
AppliedIndex, consistent with how other RaftServer methods
handle both raft implementations.
* fix(master): use LastIndex() instead of AppliedIndex() for Hashicorp Raft
AppliedIndex() reflects in-memory FSM state which starts at 0 before
log replay completes. LastIndex() reads from persisted stable storage,
correctly mirroring the non-Hashicorp IsLogEmpty() check.
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