README: protocol, fragmentation, poll and addressed-delivery diagrams;
observation fields and identity; transport, belief and trim guidance;
simulator example; constants table.
AGENTS.md: drop the completed plan's task-by-task workflow and Task 14
notes, point at both specs, use scripts/ci.sh as the gate, and update
the identity-hash constraint to include `to`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>