Need some kind of 'completion' signal.

[shans]

No description provided.

[shans]

Actually, maybe not.

We currently track the first message of each group as a stack fashion, and I think we should track the last message in a similar fashion. The last message then provides the completion signal where useful.

However, I'm unsure about things like this:

A1ToN -> BNTo1 -> C
A1ToN -> C

What comes out of A1ToN is a message with [{start: true, end: false}]
then some messages with [{start: false, end: false}]
then [{start: false, end: true}]

B will merge these, so a single message [{start: true, end: true}] comes out.
C then sees two groups. At this level things seem OK, but what about much more complicated nesting?

At some point I think groups will need to be identified too. So the first group going through C will be tagged as originating at B, and the second as originating at A.