atriumatrium

Panes & mosaic

The tiling layout, splits, subtabs, and pane lifecycle.

Inside a room, panes are arranged in a mosaic — a binary tree of horizontal and vertical splits, with panes at the leaves. You can split, swap, resize, maximize, and group panes without leaving the keyboard.

Splitting

  • Cmd+D splits the focused pane right (horizontal split — new pane to the right).
  • Cmd+Shift+D splits the focused pane down (vertical split — new pane below).
  • Drag a pane header onto another pane's edge to drop into that zone (left, right, top, bottom).
  • Drop onto the center of another pane's header to stack the pane as a subtab.

Resizing, swapping, equalizing

  • Drag split dividers with the mouse or trackpad.
  • Right-click a split divider for Swap, Equalize, and Lock/unlock.
  • Maximize a pane (double-click its divider or use the pane header menu) to hide siblings. Restore with the same action.

Focus and navigation

  • Cmd+[ / Cmd+] cycle focus to the previous / next pane within the room.
  • Click any pane to focus it. The focused pane shows a subtle accent ring.
  • atrium pane focus <id> from the CLI.

Subtabs

Panes of the same type can be grouped under one header slot. Drop a pane onto another pane's header to stack them.

  • Click a subtab to switch to it.
  • Drag a subtab out of the group to split it off into its own pane.
  • Close a subtab with the × button; the group stays alive as long as another subtab exists.

Pane identity

Each pane has an immutable UUID. The pane header displays an auto-generated title (for example editor: main.rs or Claude Code — session abc123). Override it with atrium pane rename <id> --name <name>; the custom title is persisted with the pane.

Lifecycle

  • Create — opened by a keyboard shortcut, drag gesture, launcher action, or atrium pane create.
  • Hide — a pane that sits in a room other than the active room is kept in the DOM so its state (scrollback, editor buffer, running process) survives instant switching.
  • Unmount — after 10 seconds hidden, a pane's React components are unmounted to free memory. State is preserved and restored on remount.
  • Close — Cmd+W or atrium pane close <id>. Closing a pane with unsaved changes or a running process prompts for confirmation.
  • Error isolation — a crash in one pane does not propagate to other panes or the app shell.

Popout

Any non-browser pane can be popped out of the mosaic into a floating overlay layered above the mosaic but below toasts and dialogs. The pop-out button lives in the pane header; once detached, the pane keeps the same header (focus ring, split, search, close) so it behaves exactly like an in-mosaic pane — just floating. Popped panes can be docked back, hidden, or shown all-at-once via Expose mode. Position, size, and which panes are out persist across restarts. See Shortcuts → Pane popout for the full keyboard surface.

Persistence

The entire mosaic tree for each room is serialized to that room's snapshot. Pane-specific state (cwd, scrollback, session ID, editor buffer position, browser URL and history) lives in per-pane JSON inside the workspace snapshot. See Persistence & recovery.

File drop

Drag a file from Finder onto atrium:

  • Dropped on the app with no existing pane for that file → opens an editor pane for it.
  • Dropped on a pane's header → opens the file as a subtab under that header.
  • Dropped on a pane's edge zone → opens the file as a new split.
atrium intercepts macOS drag-and-drop at the OS level; some web drag events do not fire. The UI uses pointer events to preview drop zones.