#readable returns false for an agent session, so a `*` share no longer shows a user's message
in an agent's trail. New tests: a sharee's session.list refuses (Q1), and an agent bound to the
shared thread, a chief run and the tester match no share (Q2). BUILD.md records the Q1
follow-up, Q2-Q4 and the live --migrate as Mos's go under Q173. README names the agent rule.
thread_shares (row 193 design 5.2) with its index and append-only triggers; the
3l-3m step only adds them. thread.share, thread.unshare and thread.shares for a
thread's owner; #readable holds design 5.4's four rules, #threadRead serves
thread.messages only, and thread.list {shared:true} adds owner. replies and
trail show shared user threads to the owner and readers. COUNTED, LISTED,
timedTables and the clock list take the table. Tests: thread-shares.test.mjs
and the 3l→3m pins. Packet agents/launchpad/work/queue-206/BUILD.md. Not run
yet: node waits for Sage's CLEAR (sage-2789).
jason.woltje