From BOLT#2 (rev 8ee09e749990a11fa53bea03d5961cfde4be4616):
Thus each node (conceptually) tracks:
...
3. Two *unacked changesets*: one for the local commitment (their proposals) and one for the remote (our proposals)
4. Two *acked changesets*: one for the local commitment (our proposals, acknowledged) and one for the remote (their proposals, acknowledged).
(Note that an implementation MAY optimize this internally, for
example, pre-applying the changesets in some cases).
In our case, we apply the unacked changes immediately into
staging_cstate, and save them in an unacked_changes array. That array
gets applied to staging_cstate as soon as it's acked (we only allow
one outstanding update_commit, so we only need one array).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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