feat(workspaces): sync the home tile layout per device orientation

The Win8-Start home grid's arrangement now syncs from the backend's
home-tile-layout plugin: ONE shared document per device orientation
(wide = landscape/desktop, tall = portrait/mobile) — every landscape
device renders the same layout, every portrait device the same other
one. localStorage persistence is retired (no migration — devices start
from the shared document; the first arrangement creates it).

- adapter/tile-layout-http.ts: the injected HTTP edge (GET/PUT/DELETE
  /home/tile-layout/:mode), the features/layout adapter's pattern
- tile-layout-store: server-backed, keyed by geometry mode — boot +
  orientation-change probes (stale in-flight responses never land),
  locally-applied edits + debounced full-document PUT with rollback to
  the last server document, WS push filtered to the active orientation,
  quiet ephemeral degrade when the backend is unreachable (no error UI),
  sync gated while a probe is in flight
- WorkspacesHome locks the store's orientation to the resolved grid
  geometry (the landscape/portrait split IS the device-type split)
- app store: the tile store lives beside the layout store; the WS
  dispatch feeds 'tile-layout' broadcasts into it; 'tiles' prop from
  App.svelte (the page entry owns the httpBase)
- ws adapter: the 'tile-layout' server message (parse guard) + socket
  handler; wire conformance case

2 files changed, 28 insertions, 0 deletions

diff --git a/src/adapters/ws/index.ts b/src/adapters/ws/index.ts
index 3713c8c..4dc0104 100644
--- a/src/adapters/ws/index.ts
+++ b/src/adapters/ws/index.ts
@@ -6,6 +6,7 @@ import type {
   ConversationStatusChangedMessage,
   ExtensionsChangedMessage,
   LayoutChangedMessage,
+  TileLayoutChangedMessage,
   WsClientMessage,
 } from "@dispatch/transport-contract";
 import type { SurfaceServerMessage } from "@dispatch/ui-contract";
@@ -40,6 +41,12 @@ export interface SurfaceSocketOptions {
    * tree for one workspace. The consumer filters by its active workspace.
    */
   onLayout?: (msg: LayoutChangedMessage) => void;
+  /**
+   * Broadcast after every successful home tile-layout write: the FULL
+   * document for one device orientation (wide/tall). The consumer filters by
+   * its active geometry mode.
+   */
+  onTileLayout?: (msg: TileLayoutChangedMessage) => void;
   onReopen?: () => void;
   socketFactory?: (url: string) => WebSocketLike;
 }
@@ -92,6 +99,8 @@ export function createSurfaceSocket(opts: SurfaceSocketOptions): SurfaceSocketHa
           opts.onExtensionsChanged?.(msg as ExtensionsChangedMessage);
         } else if (msg.type === "layout") {
           opts.onLayout?.(msg as LayoutChangedMessage);
+        } else if (msg.type === "tile-layout") {
+          opts.onTileLayout?.(msg as TileLayoutChangedMessage);
         } else {
           opts.onMessage(msg as SurfaceServerMessage);
         }
diff --git a/src/adapters/ws/logic.ts b/src/adapters/ws/logic.ts
index 6cbc559..4dbd173 100644
--- a/src/adapters/ws/logic.ts
+++ b/src/adapters/ws/logic.ts
@@ -6,6 +6,7 @@ import type {
   ConversationStatusChangedMessage,
   ExtensionsChangedMessage,
   LayoutChangedMessage,
+  TileLayoutChangedMessage,
   WsClientMessage,
   WsServerMessage,
 } from "@dispatch/transport-contract";
@@ -28,6 +29,7 @@ const VALID_SERVER_TYPES = new Set([
   "conversation.compacted",
   "extensions-changed",
   "layout",
+  "tile-layout",
 ]);
 
 /** Serialize a client message to a JSON string for the wire. */
@@ -206,6 +208,23 @@ export function parseServerMessage(data: string): WsServerMessage | null {
       };
       return msg;
     }
+    case "tile-layout": {
+      // Home tile-layout broadcast (the synced home grid): the FULL document
+      // for ONE device orientation. Light shape checks here (the document's
+      // structural validation is the backend's write-time job); the store
+      // filters by its active geometry mode.
+      if (parsed.mode !== "wide" && parsed.mode !== "tall") return null;
+      const data = parsed.data;
+      if (data === null || !isRecord(data) || data.version !== 2 || !Array.isArray(data.tiles)) {
+        return null;
+      }
+      const msg: TileLayoutChangedMessage = {
+        type: "tile-layout",
+        mode: parsed.mode,
+        data: data as unknown as TileLayoutChangedMessage["data"],
+      };
+      return msg;
+    }
     default:
       return null;
   }