Close an exchange with a message, and owe one kind of activation (#66)

[andreisavu]

A close of an exchange was a row beside the messages. The summary it owed
had its own id shape, its own fold, its own retry accounting and its own
set of end reasons. A pending wake had the same four things, written once
more. Two machines answered one question: which activation does the room
owe a seat, and when.

A close is now a closed message on the record. It holds its person and
the range it turned out to cover, it carries the assistant in wakes when
the exchange owes a summary, and it reaches that seat the way every other
message reaches one. So:

• One fold answers every activation the room owes (dueActivations in
  room/lease.ts). foldOwed, Owed, judged, withAttempts and the
  second "came to nothing" set are gone, and room/fold.ts drops from 250
  lines to 115.
• One id shape names every activation, so parseId has one variant and
  seatOf no longer takes the assistant's name to read an id.
• What an activation may do is read off the message that woke it
  (handOf in room/view.ts), rather than off the spelling of its id.
• The log holds four kinds of entry, and wire.ts holds one row type less.
• messages() holds every exchange boundary, so a host reads the history
  of exchanges from one read. Before this, a closed exchange was legible
  only on the event stream or by reaching past Ambion into Pi's session.

Two behaviours changed with it.

A running lease answers a close the way it answers any other message, so a
resumed room waits for a dead run's draft lease to expire instead of
re-sending the wake at once. Backlog item 30 is the same wait.

quiet means what it says: a seat is live through its backoff, a draft
included, so the room reports quiet only once it owes nothing. That
closes backlog item 43. The routing's compose guard now asks whether the
assistant holds a live lease, so a question that lands inside a draft's
backoff still wakes it to compose.

The chaos sweep on both storages, the handover under load, 200 seeds of
the walk and the history, and the full gate all pass. test/support/chaos.ts
read the leases a dead run left after resuming the name, which let a claim
of the new run's count as inherited; it reads them before the run exists.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01XHJVkbjScXStrKhY27Xjtd