Friction signals of agent coordination, counted locally for the retro
loop: <data>/agents/friction.jsonl, one {"at", "signal", "agent"?, "root"?} line per event (fixed keys and ids, never message text),
summed by lean-ctx agent friction [--since <dur>] and per hour, worker
and vault by the Hive connector’s friction counter for the vault bus
(V16.1).
Mirror of a host’s own agent-to-agent message (Claude Code SendMessage)
onto the local bus scratchpad, so ctx_agent read and the dashboard see
direct traffic the host delivers outside lean-ctx.
Metadata key under which a bus message carries its admission binding. The
on-disk shape of ScratchpadEntry is unchanged: metadata already is a
string map, and an entry written before bindings existed simply has no
such key (the legacy rule of context_admission::stored applies to it).