Panes
Multi-pane layouts let you run several conversations in parallel inside the same terminal. Each pane is a viewport (vim "window") bound to a conversation (vim "buffer"): it has its own agent, scrollback, in-flight turn, and command queue. Different panes can show different conversations at once. Layouts are an N-ary tree of leaves (panes) and split nodes (vertical or horizontal containers), mutated only through chord keys and the /pane command.
Single-pane default
Launching arbiter opens one pane covering the whole terminal, bound to the last-active conversation. The hint row at the bottom shows esc interrupt · pgup/dn scroll · /agents · /help. Plain text goes to the focused (only) pane's current agent.
Splitting
| Chord | Effect |
|---|---|
^W v | Vertical split — focused pane becomes left, new pane on the right. |
^W h | Horizontal split — focused pane becomes top, new pane on the bottom. |
Splits divide the focused pane's rect equally (or by drag-adjusted weights). The new pane inherits the focused pane's conversation (same buffer in a new window); switch with /chat switch or the history sidebar. New panes use the index master agent by default; change with /use <agent>.
In multi-pane layouts the compact chord hint (^W w focus · ^W z zoom · ^W c close) paints on the focused column's outer-bottom pane (including when focus is mid-stack). Every pane on the layout's outer bottom keeps the same footer pad so column bottoms stay aligned; panes stacked above that edge use no trailing pad so the gutter is a single separator cell — the same rhythm as vertical splits. Outer-top panes keep a one-row output float (matching the sidebar inset); panes below a horizontal split start flush. With layout.chrome_compact_rows (the default), pad is reclaimed only when show_footer is off — set "chrome_compact_rows": false in tui.json / a theme file to keep blank placeholders when the footer is disabled.
Splitting twice in the same orientation does not wrap a new node — the new sibling is appended to the existing split, so N panes share 1/N each. Splitting in the other orientation wraps the focused leaf in a fresh 2-child node.
Focus
| Chord | Effect |
|---|---|
^W w / ^W ^W | Cycle focus to the next pane (pre-order traversal). |
Exactly one pane is focused at any moment. The focused pane's bottom border draws with an accent colour and owns the readline; inactive panes are content-only (no input box). Stacked gutters are a single separator cell — the same spacing as vertical splits.
Unfocused panes show a small activity badge on the mid-separator when a turn is running (●) or when a turn completes while you were elsewhere (✓ / ✗). The badge clears when you focus that pane.
PgUp/PgDn scroll the focused pane. Esc cancels the focused pane's in-flight turn — siblings keep streaming.
Zoom
| Chord | Effect |
|---|---|
^W z | Toggle maximize on the focused pane. Siblings stay open; press again to restore. |
Zoom is a rendering override — the layout tree is unchanged. Cycling focus while zoomed moves the maximized pane; splitting or closing clears zoom first.
Closing
| Chord | Effect |
|---|---|
^W c | Close the focused pane. Last remaining pane cannot be closed. |
Close is graceful: the pane's command queue is stopped, its in-flight turn is cancelled, the exec thread is joined outside layout_mu (so an in-flight /pane spawn or present_all on that thread cannot deadlock the close), child parent_pane links are cleared, and only then is the Pane destroyed. Join can still briefly wait for the cancelled turn to unwind. Pending output for that pane is dropped.
When closing collapses a split node to a single child, the child takes the parent's slot in the tree (no orphan single-child split nodes). Focus moves to the nearest leaf.
Conversations and panes
Switching conversations (^W b → Enter, or /chat switch) attaches the selected conversation to the focused pane only. Sibling panes keep their conversations and the split layout stays intact. /chat new creates a fresh conversation on the focused pane.
If the focused pane has a turn in flight, the TUI asks Turn in progress — switch anyway? [y/N]. Confirming cancels that pane's in-flight request (sibling panes keep streaming), shows a cancelling… spinner, and returns to the normal input loop while the turn unwinds. Esc / Ctrl-C abandons the pending switch; queued follow-up commands on the pane are kept unless the switch completes. Deleting a conversation that is currently shown behaves the same way for every pane bound to it.
Agent message histories are keyed per conversation, so two panes can stream different threads concurrently without resetting each other.
/pane — programmatic spawn
/pane <agent> <msg> spawns a new pane running <agent> with <msg> as its first input. Differs from ^W v/h in three ways:
- The new pane gets a specific starting message instead of an empty prompt.
- The result of that first message flows back to the spawning pane as a
[PANE RESULT]message when the child completes (the spawner can keep typing while the child works). - Layout: the new pane is appended as a sibling using the spawner's parent's orientation, or wraps the spawner in a 2-child vertical split if the spawner is the root.
Agents themselves can emit /pane <agent> <msg> in their replies. The orchestrator parses it and the layout pane spawn fires the same way — child runs, result comes back as a tool result. Useful when the master agent wants to fan out work to a subagent without blocking its own turn.
Independence and shared state
Independent per-pane:
- Bound conversation id
- Agent and current model
- Scrollback ring
- In-flight turn (one at a time per pane; queue subsequent inputs)
- Status bar, indicators
- Token counter
Shared across all panes:
- Tenant identity (when running against a remote API)
- Agents catalogue (
/create//removeaffects every pane immediately) - Loops (
/loops,/log, etc. operate on the global loop manager) - The shared scratchpad (
/mem shared) - Per-conversation agent histories (shared when two panes bind the same conversation)
Mouse
When layout.mouse is enabled in ~/.arbiter/tui.json (the default), the TUI enables SGR mouse tracking and consumes:
| Action | Effect |
|---|---|
| Left-click a pane | Focus that pane (also exits history-sidebar focus) |
| Left-click the input row | Focus the pane and place the caret |
| Left-click an expandable block | Expand or collapse thinking / tool / truncated code |
| Drag across scrollback | Select text; release copies via OSC 52 (Esc clears) |
| Wheel over scrollback | Scroll that pane (does not steal keyboard focus) |
| Left-click a conversation in the history sidebar | Select and switch to it |
| Drag a split gutter | Resize the two adjacent panes asymmetrically |
| Right sidebar | Display-only — clicks and wheel over it are ignored |
Set "layout": { "mouse": false } to keep keyboard-only input (useful inside tmux without set -g mouse on, or when the host terminal fights with mouse capture). Text selection copy uses OSC 52; under tmux enable set -g set-clipboard on (or an equivalent clipboard passthrough).
Limits
- No keyboard shortcut yet to resize a split asymmetrically (mouse drag works; see above). Chord-based weights are tracked as #44.
- Layout is persisted to
~/.arbiter/conversations/layout.json(tree shape, split weights, per-pane conversation id + agent). Relaunch restores the arrangement and replays each distinct(conversation_id, agent)transcript tail (shared-conversation siblings keep empty scrollback, matching live splits); painted scrollback and zoom are not saved. See Sessions.