ADR 0141: Make Expanded Sidebar Width User-Resizable

• Status: Accepted (amended by ADR 0290)
• Date: 2026-09-01

Context

The sidebar's fixed expanded width makes long project names and session titles hard to inspect, while a permanently wider sidebar wastes space for compact workspaces. The shell already owns sidebar layout and collapse state, so width preference state belongs at the same renderer boundary.

Decision

The expanded sidebar exposes a resize handle on its right edge. Pointer motion previews a width anchored to the pointer-down position and the main pane reflows continuously. The width is rounded and clamped to 240px..520px, with a 275px default; only pointer release persists the preferred width under the sidebar renderer preference storage.

The handle is an ARIA vertical separator. It supports ArrowLeft/ArrowRight with 16px steps, Home, and End. Keyboard changes commit immediately. Escape, pointer cancellation, lost ownership, and component unmount restore the width captured at pointer-down. Collapsing the sidebar preserves the preferred expanded width.

Consequences

• Users can choose a comfortable sidebar width without changing native window bounds or work-panel reservation behavior.
• The renderer remains the sole owner of sidebar width, avoiding a new IPC contract and keeping native window edge resize independent.
• A small edge hit area and visible focus/hover rule add a discoverable control without changing the dense sidebar row layout.

Alternatives considered

• Fixed width: rejected because it prevents users from accommodating long project/session labels or reclaiming unused sidebar space.
• Native window reservation or a second resize channel: rejected because the sidebar is an in-flow renderer column and its width should only reflow the main pane.