tree a0b9eb0f68de826d7b51a5e8f5eaa7976fb48de3
parent 5228b5850d8453c225e5611918fcd00b747c65cc
author Philip Zeyliger <philip@bold.dev> 1746119417 -0700
committer Philip Zeyliger <philip@bold.dev> 1746126811 -0700

agent plumbing: convert outbox to subscribers and an iterator

WaitForMessage() could only work for one thread, because it was using a
singular channel for outboxes. This was fine when we only had one user,
but WaitForMessageCount() was kinda similar, and had its own thing, and
I want to rework how polling works and need another user.

Anyway, this one is hand-coded, because Sketch really struggled
with getting the iterator convincingly safe. In a follow-up commit,
I'll try to get Sketch to write some tests.