buffer tracer that monitors the buffers and contents for any changes. The AST
for each (dirty) buffer is sent out at conflict resolution and after the
cycle has elapsed.
As currently implemented, we mark buffers as dirty inline, but then flush
them on the background thread. This opens the possibility to mismatches due
to a late flush. It would probably be better to mark them inline, package
them inline, but dispatch the message on the background thread (hopefully
ensurely in order receipt)