Companion View

A companion is a secondary region the view layer displays alongside a node's primary master-detail navigation: a chat panel beside a gaming session, a property inspector beside a document editor, or a reference pane beside a campaign tree.

Unlike popovers or modal drawers, a docked companion lives in normal layout flow: it reserves real layout space, causing adjacent navigation columns to compact smoothly without obscuring content.

A domain node opts into displaying a companion by answering the optional protocol method:

nodeCompanionNode () {
    return this.someOwnedCompanionNode(); // returns the companion root node, or null for none
}

The node specifies which node to show alongside itself, but zero UI details: width, axis, pinning, and collapse state are managed entirely by the view layer. This maintains strict headless testability.

SvDetailView arbitrates layout space using setAvailableLength():

• Threshold Check: If available width falls below tabLength, mode switches to hidden.
• User Pinning: Clicking the edge handle toggles between docked and tab, persisting the choice as userMode.
• Shortcut: Pressing Meta+\\ (Cmd+\\ or Ctrl+\\) toggles the deepest visible companion in the active navigation chain.

SvStackView
 └─ SvDetailView                       (owns space arbitration)
     ├── childStackView                (primary flexible navigation)
     └── SvCompanionView              (node = nodeCompanionNode())
         ├── contentView              (embedded isolated SvBrowserView)
         ├── SvEdgeHandleView         (collapse/expand handle)
         └── SvCompanionTabView       (internal badge plumbing)

• Responsive Views: Viewport compaction and column collapse.
• Auto-Generated Views: Miller column stack containers.