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ADR 0238: Prioritize MainChat in the three-column shell ​

Context ​

The renderer shell has three in-flow columns inside a fixed client area: the expanded sidebar, MainChat and the work panel. ADR 0033 and ADR 0151 keep native window bounds out of the panel's reach, but the shell still has no explicit width priority. The 515px chat reservation of ADR 0226 and the fixed 244px–720px panel range left pointer resizing, keyboard resizing, sidebar toggles and window resizing with different rules, and a narrow window could pin MainChat to its floor while the expanded sidebar kept its full width.

Decision ​

  1. MainChat has a hard 450px minimum, derived from the composer toolbar's unfolded row (plus button, mode and permission chips, model/thinking chip, enhance and send buttons) plus its margins. The work-panel maximum is the remaining client width after that floor and the expanded sidebar (clientWidth - mainChatMinimum - expandedSidebarWidth); there is no fixed pixel cap, so a wide window keeps spending width on the panel until MainChat reaches its floor. The shared renderer budget function is used by pointer preview, keyboard resize, panel presentation, sidebar changes and shell resize observation.
  2. When the expanded sidebar would make MainChat reach the 450px floor, the renderer immediately collapses the sidebar through the existing mounted sidebar-out animation. While that animation still occupies flex space, the shared budget continues to count the sidebar so MainChat stays at or above 450px. The preferred work-panel width remains the user's persisted target, so the panel can continue growing after the sidebar has yielded.
  3. A manual sidebar reopen spends work-panel width first. It preserves the current MainChat width where possible; if the 450px floor would be crossed, it targets 460px. This reopen path may persist a positive compact panel width below the ordinary 244px presentation minimum.
  4. Automatic sidebar collapse is remembered only until the work panel closes. Closing the panel restores a sidebar collapsed by the layout mechanism. Manual sidebar collapse, manual reopen and a subsequent manual collapse clear that record.
  5. The window itself stays fixed. No panel action requests a positive native reservation: the renderer keeps window/setWorkPanelReservation at zero and Main normalizes every valid request to { requested: 0, reserved: 0 } without applying panel width or x-offset geometry (ADR 0033 / ADR 0151). The supported window minimum stays 1040×700, which already exceeds mainChatMinimum + panelMinimum, so the panel minimum is satisfiable at every supported window size.
  6. The panel header exposes a preview (maximize) toggle. While preview mode is on, MainChat is not rendered at all and the panel takes the whole client area beside the sidebar (clientWidth - expandedSidebarWidth); the 450px MainChat floor is therefore suspended by design, because there is no chat column to protect. Leaving preview mode restores the previous panel width and keeps whatever sidebar state the user chose last; the mode is transient (never persisted, ends with the panel) and never changes native bounds. Because MainChat is absent in this mode, AppShell supplies a window-level 46px chrome row with New Task, sidebar, and native window controls. Collapsed-sidebar preview reserves the shared --ds-window-lead-inset on the left: 88px in windowed macOS and 8px in fullscreen (D433). Hit-region amendment (2026-09-16): the chrome row and its spacer declare neither drag nor no-drag, and pass pointer events through outside controls. The panel header is the sole drag owner within the preview pane. Its actual border box excludes the left shell-action lane plus an 8px gap in both sidebar states, including expanded-sidebar New Task. All platforms use an 8px left inset except collapsed-sidebar windowed macOS (88px). The existing right native-control border exclusion remains unchanged. Header-height background paint fills the excluded lane without an opaque control overlay. Native pointer clicks and window dragging require native validation; renderer geometry and DOM/CDP event dispatch are not native hit-test proof.

Consequences ​

  • MainChat cannot be compressed below 450px by any supported shell width change; the sidebar is the column that yields.
  • A constrained window shows a narrower work panel during the current layout, while the persisted preferred width remains available when space returns.
  • The composer toolbar now handles widths between 450px and its comfortable layout instead of relying on a 515px reservation, so its control groups ellipsize or reflow below that width.
  • No host protocol, SQLite schema, plugin contract, security boundary or native window geometry changes.

Alternatives rejected ​

Keep the 515px chat reservation of ADR 0226 ​

Rejected because it leaves side-dock priority implicit and cannot satisfy the 450px hard floor with automatic sidebar-yield behaviour, which is what keeps MainChat usable in the fixed window.

Let the sidebar resize continuously to preserve every column ​

Rejected because the sidebar remains a discrete expanded/collapsed column for this interaction. Its user-selected preferred width is not silently mutated by window pressure.

Mirror the committed panel width into native window bounds ​

Rejected because expanding the application window is the outward behaviour ADR 0033 and ADR 0151 removed. The window minimum already guarantees mainChatMinimum + panelMinimum, so the budget is always satisfiable without touching native bounds.

References ​

  • apps/desktop/src/lib/work-panel-resize.ts
  • apps/desktop/src/components/workpanel/WorkPanel.tsx
  • apps/desktop/src/features/app/useAppShellRuntime.tsx
  • apps/desktop/src/features/app/AppShell.tsx
  • apps/desktop/src/styles/chat-shell.css

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