Update documentation and revert type change

Author: martinalong

specification/draft/apps.mdx

@@ -456,18 +456,17 @@ interface HostContext {
   displayMode?: "inline" | "fullscreen" | "pip";
   /** Display modes the host supports */
   availableDisplayModes?: string[];
-  /**
-   * Viewport dimensions available to the UI.
-   *
-   * The viewport has two independent dimension pairs:
-   * - Height: Either `height` (fixed) or `maxHeight` (flexible), never both
-   * - Width: Either `width` (fixed) or `maxWidth` (flexible), never both
-   *
-   * Fixed dimensions (height/width): The host controls the size. Set height: 100% (recommended) or use the pixel value directly.
-   * Flexible dimensions (maxHeight/maxWidth or undefined): The app controls the size, up to the max if specified.
-   */
-  viewport?: ({ height: number } | { maxHeight?: number }) &
-    ({ width: number } | { maxWidth?: number });
+  /** Current and maximum dimensions available to the UI. */
+  viewport?: {
+    /** Current viewport width in pixels. */
+    width: number;
+    /** Current viewport height in pixels. */
+    height: number;
+    /** Maximum available height in pixels (if constrained). */
+    maxHeight?: number;
+    /** Maximum available width in pixels (if constrained). */
+    maxWidth?: number;
+  };
   /** User's language/region preference (BCP 47, e.g., "en-US") */
   locale?: string;
   /** User's timezone (IANA, e.g., "America/New_York") */

src/app-bridge.test.ts

@@ -113,7 +113,7 @@ describe("App <-> AppBridge integration", () => {
       const testHostContext = {
         theme: "dark" as const,
         locale: "en-US",
-        viewport: { width: 800, maxHeight: 600 },
+        viewport: { width: 800, height: 600, maxHeight: 600 },
       };
       const newBridge = new AppBridge(
         createMockClient() as Client,
@@ -337,7 +337,7 @@ describe("App <-> AppBridge integration", () => {
       const initialContext = {
         theme: "light" as const,
         locale: "en-US",
-        viewport: { width: 800, maxHeight: 600 },
+        viewport: { width: 800, height: 600, maxHeight: 600 },
       };
       const newBridge = new AppBridge(
         createMockClient() as Client,
@@ -356,7 +356,7 @@ describe("App <-> AppBridge integration", () => {
 
       // Send another partial update: only viewport changes
       newBridge.sendHostContextChange({
-        viewport: { width: 1024, maxHeight: 768 },
+        viewport: { width: 1024, height: 768, maxHeight: 768 },
       });
       await flush();
 
@@ -367,7 +367,11 @@ describe("App <-> AppBridge integration", () => {
       const context = newApp.getHostContext();
       expect(context?.theme).toBe("dark");
       expect(context?.locale).toBe("en-US");
-      expect(context?.viewport).toEqual({ width: 1024, maxHeight: 768 });
+      expect(context?.viewport).toEqual({
+        width: 1024,
+        height: 768,
+        maxHeight: 768,
+      });
 
       await newAppTransport.close();
       await newBridgeTransport.close();

src/generated/schema.json

@@ -313,18 +313,17 @@ export interface McpUiHostContext {
   displayMode?: McpUiDisplayMode;
   /** @description Display modes the host supports. */
   availableDisplayModes?: string[];
-  /**
-   * @description Viewport dimensions available to the UI.
-   *
-   * The viewport has two independent dimension pairs:
-   * - Height: Either `height` (fixed) or `maxHeight` (flexible), never both
-   * - Width: Either `width` (fixed) or `maxWidth` (flexible), never both
-   *
-   * Fixed dimensions (height/width): The host controls the size. Set height: 100% (recommended) or use the pixel value directly.
-   * Flexible dimensions (maxHeight/maxWidth or undefined): The app controls the size, up to the max if specified. If undefined, there is no limit.
-   */
-  viewport?: ({ height: number } | { maxHeight?: number }) &
-    ({ width: number } | { maxWidth?: number });
+  /** @description Current and maximum dimensions available to the UI. */
+  viewport?: {
+    /** @description Current viewport width in pixels. */
+    width: number;
+    /** @description Current viewport height in pixels. */
+    height: number;
+    /** @description Maximum available height in pixels (if constrained). */
+    maxHeight?: number;
+    /** @description Maximum available width in pixels (if constrained). */
+    maxWidth?: number;
+  };
   /** @description User's language and region preference in BCP 47 format. */
   locale?: string;
   /** @description User's timezone in IANA format. */