Specification: pane.swap and pane.move

Created: 2026-10-10. Status: clarified.

herdr scripts can swap two panes and move a pane next to another. In signaltty the only way is tab.set_layout, which works within one tab and cannot change the tab a pane belongs to.

Acceptance

1. pane.swap {pane_id, target_pane_id} exchanges the two panes' slots. The tree shape and the ratios do not change. Across tabs, each pane changes tab and each tab's focus stays on its slot.
2. pane.move {pane_id, target_pane_id, direction?} removes the pane from its layout, collapsing the parent split, and splits the target with it (right by default), evening out the run like pane.split. A source tab left without panes is empty, as after pane.close.
3. Processes, PTYs and output are untouched. Each touched tab emits tab.updated. A pane that changed tab emits pane.updated. The result is {tabs}.
4. The same pane twice, panes in different workspaces, or a pane that is not in its tab layout → BAD_PARAMS. An unknown pane → NO_SUCH_PANE.
5. Both are in docs/08, method::ALL, the CLI (pane swap, pane move) and integration tests.

Scope and clarification

Moves across workspaces are out of scope. A workspace owns its cwd and git state, so a pane would carry a stale context. herdr's pane.zoom is not added. Zoom in signaltty is a per-window GUI view that is cleared on navigation, so a server flag would fight it.