M7: Nil out trailing *connectionEntry pointers in the backing array
after slice removal in removeConnectionAtIndexLocked and send().
Without this, the GC cannot collect removed entries until the slice
is reallocated.
M1: Initialize the done channel in NewBatcher instead of Start().
Previously, calling Close() or queueWork before Start() would select
on a nil channel, blocking forever. Moving the make() to the
constructor ensures the channel is always usable.
M2: Move b.connected.Delete and b.totalNodes decrement inside the
Compute callback in cleanupOfflineNodes. Previously these ran after
the Compute returned, allowing a concurrent AddNode to reconnect
between the delete and the bookkeeping update, which would wipe the
fresh connected state.
M3: Call markDisconnectedIfNoConns on AddNode error paths. Previously,
when initial map generation or send timed out, the connection was
removed but b.connected retained its old nil (= connected) value,
making IsConnected return true for a node with zero connections.
Updates #2545
50e8b21471