fix(app-bridge): v1 parity — setHostContext diffing, hostContext accumulate, onclose shim, onupdatemodelcontext return type, getToolUiResourceUri error message

Author: felixweinberger

src/app-bridge.ts

@@ -159,6 +159,7 @@ const BRIDGE_EVENT_NOTIFICATION_SCHEMAS: Record<
  */
 export function isToolVisibilityModelOnly(tool: {
   _meta?: Record<string, unknown>;
+  [key: string]: unknown;
 }): boolean {
   const v = (tool._meta?.ui as McpUiToolMeta | undefined)?.visibility;
   return Array.isArray(v) && v.length > 0 && !v.includes("app");
@@ -169,6 +170,7 @@ export function isToolVisibilityModelOnly(tool: {
  */
 export function isToolVisibilityAppOnly(tool: {
   _meta?: Record<string, unknown>;
+  [key: string]: unknown;
 }): boolean {
   const v = (tool._meta?.ui as McpUiToolMeta | undefined)?.visibility;
   return Array.isArray(v) && v.length > 0 && !v.includes("model");
@@ -219,6 +221,8 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
 
   /** Optional error handler. Mirrors the v1 `Protocol.onerror` slot. */
   onerror?: (error: Error) => void;
+  /** Called when the underlying transport closes. Mirrors v1 Protocol.onclose. */
+  onclose?: () => void;
 
   constructor(
     private _client: Client | null,
@@ -239,6 +243,7 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
       },
     });
     this.server.onerror = (err) => this.onerror?.(err);
+    this.server.onclose = () => this.onclose?.();
     this.ui = this.server.extension(MCP_APPS_EXTENSION_ID, _capabilities, {
       peerSchema: McpUiAppCapabilitiesSchema,
     });
@@ -447,7 +452,7 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
   private _onupdatemodelcontext?: (
     params: McpUiUpdateModelContextRequest["params"],
     extra: RequestHandlerExtra,
-  ) => Promise<void> | void;
+  ) => Promise<void | object> | void | object;
   get onupdatemodelcontext() { return this._onupdatemodelcontext; }
   set onupdatemodelcontext(cb) {
     this.warnIfRequestHandlerReplaced(
@@ -552,8 +557,13 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
    * Call this when theme, locale, displayMode, etc. change.
    */
   setHostContext(context: Partial<McpUiHostContext>) {
+    const changed: Partial<McpUiHostContext> = {};
+    for (const [k, v] of Object.entries(context) as [keyof McpUiHostContext, unknown][]) {
+      if (this._hostContext[k] !== v) (changed as Record<string, unknown>)[k] = v;
+    }
     this._hostContext = { ...this._hostContext, ...context };
-    return this.sendHostContextChanged(context);
+    if (Object.keys(changed).length === 0) return Promise.resolve();
+    return this.sendHostContextChanged(changed);
   }
 
   /** Low-level: send a host-context-changed notification with the given diff. */

src/app.ts

@@ -100,11 +100,13 @@ export function getToolUiResourceUri(tool: {
   const meta = tool._meta;
   if (!meta) return undefined;
   const ui = meta.ui as { resourceUri?: unknown } | undefined;
-  const candidate = ui && "resourceUri" in ui ? ui.resourceUri : meta[RESOURCE_URI_META_KEY];
-  if (candidate === undefined) return undefined;
+  const hasNested = ui != null && "resourceUri" in ui;
+  const candidate = hasNested ? ui.resourceUri : meta[RESOURCE_URI_META_KEY];
+  if (candidate === undefined && !hasNested) return undefined;
   if (typeof candidate !== "string" || !candidate.startsWith("ui://")) {
     throw new Error(
-      "Tool _meta.ui.resourceUri must be a string starting with ui://, got: " + JSON.stringify(candidate),
+      'Invalid UI resource URI (must be a string starting with "ui://"): ' +
+        JSON.stringify(candidate),
     );
   }
   return candidate;
@@ -186,6 +188,8 @@ export class App extends EventDispatcher<AppEventMap> {
    * error. Mirrors the v1 `Protocol.onerror` slot.
    */
   onerror?: (error: Error) => void;
+  /** Called when the underlying transport closes. Mirrors v1 Protocol.onclose. */
+  onclose?: () => void;
 
   constructor(
     private _appInfo: Implementation,
@@ -198,6 +202,7 @@ export class App extends EventDispatcher<AppEventMap> {
       capabilities: { roots: undefined },
     });
     this.client.onerror = (err) => this.onerror?.(err);
+    this.client.onclose = () => this.onclose?.();
     this.ui = this.client.extension(MCP_APPS_EXTENSION_ID, _capabilities, {
       peerSchema: McpUiHostCapabilitiesSchema,
     });
@@ -247,8 +252,8 @@ export class App extends EventDispatcher<AppEventMap> {
     event: K,
     params: AppEventMap[K],
   ): void {
-    if (event === "hostcontextchanged" && this._hostContext !== undefined) {
-      this._hostContext = { ...this._hostContext, ...(params as McpUiHostContext) };
+    if (event === "hostcontextchanged") {
+      this._hostContext = { ...(this._hostContext ?? {}), ...(params as McpUiHostContext) };
     }
   }