ADR-0013: Fixed layout regions and a collapsible section stack

• Status: Accepted; amended by ADR-0035
• Date: 2026-06-24
• Deciders: jka
• Decision: D13

Context

rio's screen needs a familiar arrangement that both a GUI and a terminal can render, and that can collapse on narrow displays without a second design.

Decision

The layout has a fixed set of logical regions:

• nav (left): files and git.
• editor (centre): tabbed, splittable into two editor groups.
• chat (right): the agent conversation, its input, and proposed edits. Command output the agent needs to show appears here; there is no terminal region (ADR-0015).
• status (bottom): a single always-present line.

One UI primitive, a collapsible section stack, backs both the left navigation and the narrow-mode collapse of all side panes. Layout is adjustable (visibility and sizes are remembered) but not free-form in the first version.

Consequences

• Users coming from VS Code-like editors recognise the arrangement.
• The GUI later replaced the fixed nav/chat regions with dock sites that any tool panel can move between (ADR-0035). The editor and status regions, and the rule that there is no terminal region, are unchanged.
• The collapsible section stack is a TUI concern and has not been built.