- Add Store::for_each_addressed_id (default: every id; MemStore filters)
so custody selection no longer clones every broadcast observation on
each poll.
- Factor fragment sizing into frag::plan and MAX_FRAGMENTS, used by both
frag::fragment and the exchange, and by the reassembler's bounds.
- Document `to` in the Observation::id hash input, matching the
addressed-delivery plan.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
kyle
