amethyst/docs/brainstorms/2026-03-19-deck-messages-stacked-layout-brainstorm.md

Brainstorm: Stacked Messages Layout in Multi-Deck

Date: 2026-03-19 Status: Ready for planning

What We're Building

Replace the side-by-side split-pane Messages layout (contact list + chat) with a stacked navigation in deck columns. Clicking a conversation navigates from the contact list to the chat view; a back arrow returns to the list. Single-pane (non-deck) mode keeps the current split layout.

Why This Approach

In multi-deck mode, columns can be 350-400dp wide. The current split layout allocates 280dp to the contact list, leaving only 70-120dp for the chat pane — unusable. A stacked layout gives the full column width to whichever view is active.

Key Decisions

Decision	Choice	Rationale
Layout mode	Always stacked in deck columns	Simplest, works at any column width
Single-pane mode	Keep split layout	Plenty of horizontal space in single-pane
Back navigation	Back arrow in chat header	Discoverable; Escape key already works
State management	selectedRoom in ChatroomListState already controls this	No new state needed — just show list when null, chat when selected

Architecture

Current Flow (DesktopMessagesScreen.kt)

Row {
    ConversationListPane(280dp)  // always visible
    VerticalDivider
    ChatPane(flex)               // or EmptyState
}

New Flow (Deck Mode)

// When selectedRoom == null:
ConversationListPane(full width)

// When selectedRoom != null:
Column {
    BackArrow + ChatroomHeader
    ChatPane(full width)
}

Implementation Approach

DesktopMessagesScreen already has selectedRoom state. The change is layout-only:

1. Add a compactMode: Boolean parameter to DesktopMessagesScreen
2. In deck mode (compactMode = true): show either list OR chat, not both
3. In single-pane mode (compactMode = false): keep current split Row
4. Add back arrow to ChatPane header when in compact mode
5. clearSelection() → back to list (already exists)

What Changes

Component	Change
DesktopMessagesScreen	Add compactMode param; conditional layout (Row vs when/else)
ChatPane	Add onBack callback + back arrow in header when provided
RootContent	Pass compactMode = true to DesktopMessagesScreen
SinglePaneLayout RootContent	Pass compactMode = false
ConversationListPane	No changes — already works at any width

Edge Cases

• Keyboard nav: Escape already calls clearSelection() — works as back
• New DM dialog: Opens over whichever view is active — no change needed
• Receiving DM while in list: Room appears/updates in list normally
• Receiving DM while in chat: Messages appear in real-time — no change

Open Questions

None — all decisions resolved.