atrium 0.39.0

The mod release. atrium now carries a Claude Code plugin of function hooks
inside its binary; atrium mod install writes it out once, and every claude
pane atrium spawns loads it for that session only. With the mod in the engine,
three things atrium used to infer from the transcript become certain (a pane's
status, its context fill and cost, the text of its answers), sends and wakes
stop being keystrokes, the control plane becomes typed tools, and a subagent is
a pane the human can see. Nothing changes for a pane that has no mod: the
inference and the pty path stay as they were. Six new ctl verbs carry it.

Install or upgrade with cargo install atrium, then run atrium mod install
once; atrium fleet up says in its preflight whether the mod is installed.

Added

• The mod: a Claude Code plugin in every claude pane. atrium mod install
  writes a plugin of function hooks out of atrium's binary; every claude pane
  atrium then spawns loads it (CLAUDE_CODE_PLUGIN_DIRS, with ATRIUM_BIN
  naming the atrium to call). Inside the engine it reports the pane's status
  the moment it changes (working, waiting-approval with the tool as the
  reason, waiting-prompt, idle, errored, ended), its context fill and
  cost, and the text of each answer, over the control channel with the pane's
  own token. A reported status wins over the transcript inference for two
  minutes; errored draws the border red with a ! badge and the overview
  shows ctx 41% $0.12 per agent. atrium mod status says what is installed;
  "mod": false in config.json or a fleet keeps it out.
• New ctl verbs hello, report, whoami, inbox, answer and wait:
  the first four are what the mod speaks and are about the caller only (a
  target is refused); answer reads a pane's last reported answer up the
  spawn tree, and wait polls for it, for idle, or for exit.
• Native delivery. A pane whose mod declared inbox is never typed into:
  ctl sends and bus wakes wait in the queue until the mod collects them and
  submits each through the engine's own prompt queue, which starts a turn only
  when the session is idle. A task may span lines; a pane without the mod
  keeps the pty path.
• Typed control-plane tools. With the mod, a claude pane has
  atrium_spawn, atrium_send, atrium_status, atrium_list, atrium_kill,
  atrium_board_* and atrium_bus_* as tools; each call is one atrium ctl
  run, and an ask for one of them is answered by the mod, never a dialog.
• The role section and the file guard. The mod appends an atrium:role
  section to the system prompt from whoami (pane, role, parent, mode, item,
  owned files, worktree, whether it may spawn) and refuses an Edit, Write
  or NotebookEdit outside the item's files, by real path, naming the owner.
• The /atrium pane, the decisions band, and respawn_at. Inside Claude
  Code, /atrium opens a pane with the open decisions (resolve buttons with
  hotkeys), the board and the last bus events; a band above the prompt counts
  open decisions. Fleet key respawn_at: <pct>: a pane whose context fill
  crosses it while idle gets one decision posted to its parent on the atrium
  topic, never a respawn by itself.
• Subagents as visible panes. atrium_subagent spawns a claude pane beside
  the caller, sends it the task, waits for the answer its mod reports, closes
  the pane unless kept, and returns the answer; the model's Agent tool is
  refused with a pointer to it. Fleet keys subagents (panes | native |
  deny) and subagents_keep; config key mod; ATRIUM_MOD names the
  mod's folder. The fleet preflight states the mod's line and warns when claude
  panes would load none.