Replace the single-slot inbox/outbox with FIFO deques: every emit and push is
kept and delivered oldest-first, exactly once. comfy_pull and Agent Receive now
dequeue the oldest item (empty when drained) instead of overwriting/replaying the
latest. keep_last now holds the last *delivered* message (store.peek returns
last_out). list_channels reports in_pending/out_pending depths. Docs + tests
updated for FIFO ordering.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
