Shell plugin: three-column AppFrame (drag handles and concession chain) plus the ctx.layout panel-geometry service; it registers into the runtime-owned root slot and declares sidebar, conversation, details, and conversation.empty. The sidebar is fixed-width (only details shrinks, then auto-closes); a closed sidebar retains a 56px control rail while details closes to zero width. The package also seats the theme presenter: it consumes resolved ctx.theme snapshots and projects them onto the document (html { color-scheme } for native UA chrome, body[data-ds-dark-theme] from the active color scheme, plus the theme's alias tokens as inline variables on body).

AppFrame reads the runtime Session projection: baselinesReady selects loading, a page-local SessionListState.intent selects the empty composer, and a connected Session renders through SessionProvider. The conversation and empty-state owner shares are empty; each registrant obtains business data from standard hooks and actions from its own inject face. The sidebar owner share contains only collapsed and width; navigation actions belong to sidebar's own injected service face.

The /client export surface is the plugin body (apply/inject), LayoutService, and the four owner-share interfaces. AppFrame, the panel store, and the concession solver remain package-internal; tests import internals through /src.

Model Experience

None, as the layout shell manages browser viewing state; nothing here reaches a model request.

KV Cache effect

None; this package neither assembles nor sends a provider request.

Known Limitations and Deferred Work

Details open/width state is global — it does not follow the session (arbitrated for P-I); the per-session keyed upgrade slot is reserved.
Concession-chain auto-close derives a zero width without touching the persisted open flag — the panel restores itself when the window widens; consumers must not read details.open as the rendered truth.
Scroll anchoring during squeeze reflow is not implemented — deferred with the virtualized-list project.