feat: continue tree rust family cutover

- add rust renderer/state-family scaffolds and inline compat host thinning for page tree, file tree, and picker
- route tree/filetree preflight, file projection, resource artifact, and stream delta contracts through rust plans
- preserve canonical move-order validation, file-tree search projection, and related frontend/runtime regression coverage

wolai-frontend/src/components/sidebar/tree-shell-host.tsx

@@ -13,6 +13,8 @@ export type TreeRendererFamily = "react" | "rust_family";
 
 export type TreeShellHostMode = "page" | "filetree" | "picker";
 
+const RUST_RENDERER_CONTRACT = "rust_renderer_input_v1";
+
 export type TreeShellPickerCommand = {
   kind: "next" | "previous" | "home" | "end" | "pick";
   seq: number;
@@ -118,8 +120,9 @@ export function TreeShellHost({
   const useRustHost = rendererFamily === "rust_family";
   const useIframeHost = useRustHost && Boolean(workspaceId?.trim());
   const hostKind = rendererFamily === "rust_family" ? "rust_family" : "react";
+  const rendererContract = useRustHost ? RUST_RENDERER_CONTRACT : undefined;
   const implementation = useIframeHost
-    ? "mnote_web_iframe_proxy"
+    ? "rust_inline_compat_host"
     : fallbackImplementation ??
       (rendererFamily === "rust_family" ? "react_fallback" : "react_primary");
 
@@ -130,6 +133,7 @@ export function TreeShellHost({
       data-renderer-family={rendererFamily}
       data-tree-host-kind={hostKind}
       data-tree-host-implementation={implementation}
+      data-tree-renderer-contract={rendererContract}
       data-page-tree-focused-id={mode === "page" ? (focusedDocumentId ?? "") : undefined}
       className={cn(className)}
     >
@@ -139,6 +143,7 @@ export function TreeShellHost({
           data-tree-host-mode={mode}
           data-tree-host-kind="rust_family"
           data-tree-host-implementation={implementation}
+          data-tree-renderer-contract={rendererContract}
           className="contents"
         >
           {useIframeHost && workspaceId ? (