Complete "Entering / exiting fullscreen" pattern documentation

Add `App_onhostcontextchanged_respondToDisplayMode` example showing how to
listen for display mode changes and update UI with `classList.toggle()`.

Update `App_requestDisplayMode_fullscreen` to `App_requestDisplayMode_toggle`
to show the common toggle pattern checking `availableDisplayModes` first.

Refactor full examples (pdf-server, shadertoy-server) to use
`classList.toggle(class, condition)` instead of add/remove branches.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/patterns.md

@@ -43,9 +43,15 @@ Use the SDK's style helpers to apply host styling, then reference them in your C
 
 {@includeCode ./patterns.tsx#hostStylingReact}
 
-## [TODO] Support fullscreen / exit fullscreen
+## Entering / Exiting fullscreen
 
-{@includeCode ./patterns.tsx#fullscreen}
+Toggle fullscreen mode by calling {@link app!App.requestDisplayMode requestDisplayMode}:
+
+{@includeCode ../src/app.examples.ts#App_requestDisplayMode_toggle}
+
+Listen for display mode changes via {@link app!App.onhostcontextchanged onhostcontextchanged} to update your UI:
+
+{@includeCode ../src/app.examples.ts#App_onhostcontextchanged_respondToDisplayMode}
 
 ## [TODO] Persist data (incl. widget state)
 

docs/patterns.tsx

@@ -97,15 +97,6 @@ function hostStylingReact() {
   //#endregion hostStylingReact
 }
 
-/**
- * Example: Support fullscreen / exit fullscreen
- */
-function fullscreen() {
-  //#region fullscreen
-  // TODO: Implement fullscreen support
-  //#endregion fullscreen
-}
-
 /**
  * Example: Persist data (incl. widget state)
  */
@@ -155,7 +146,6 @@ void authenticatedCalls;
 void errorsToModel;
 void hostStylingVanillaJs;
 void hostStylingReact;
-void fullscreen;
 void persistData;
 void lowerPerceivedLatency;
 void iframeAndMcpApps;

examples/pdf-server/src/mcp-app.ts

@@ -769,16 +769,12 @@ function handleHostContextChanged(ctx: McpUiHostContext) {
   if (ctx.displayMode) {
     const wasFullscreen = currentDisplayMode === "fullscreen";
     currentDisplayMode = ctx.displayMode as "inline" | "fullscreen";
-    if (ctx.displayMode === "fullscreen") {
-      mainEl.classList.add("fullscreen");
-      log.info("Fullscreen mode enabled");
-    } else {
-      mainEl.classList.remove("fullscreen");
-      log.info("Inline mode");
-      // When exiting fullscreen, request resize to fit content
-      if (wasFullscreen && pdfDocument) {
-        requestFitToContent();
-      }
+    const isFullscreen = currentDisplayMode === "fullscreen";
+    mainEl.classList.toggle("fullscreen", isFullscreen);
+    log.info(isFullscreen ? "Fullscreen mode enabled" : "Inline mode");
+    // When exiting fullscreen, request resize to fit content
+    if (wasFullscreen && !isFullscreen && pdfDocument) {
+      requestFitToContent();
     }
     updateFullscreenButton();
   }

examples/shadertoy-server/src/mcp-app.ts

@@ -65,21 +65,14 @@ function handleHostContextChanged(ctx: McpUiHostContext) {
 
   // Show fullscreen button if available (only update if field is present)
   if (ctx.availableDisplayModes !== undefined) {
-    if (ctx.availableDisplayModes.includes("fullscreen")) {
-      fullscreenBtn.classList.add("available");
-    } else {
-      fullscreenBtn.classList.remove("available");
-    }
+    const canFullscreen = ctx.availableDisplayModes.includes("fullscreen");
+    fullscreenBtn.classList.toggle("available", canFullscreen);
   }
 
   // Update display mode state and UI
   if (ctx.displayMode) {
     currentDisplayMode = ctx.displayMode as "inline" | "fullscreen";
-    if (currentDisplayMode === "fullscreen") {
-      mainEl.classList.add("fullscreen");
-    } else {
-      mainEl.classList.remove("fullscreen");
-    }
+    mainEl.classList.toggle("fullscreen", currentDisplayMode === "fullscreen");
   }
 }
 
@@ -96,11 +89,7 @@ async function toggleFullscreen() {
   try {
     const result = await app.requestDisplayMode({ mode: newMode });
     currentDisplayMode = result.mode as "inline" | "fullscreen";
-    if (currentDisplayMode === "fullscreen") {
-      mainEl.classList.add("fullscreen");
-    } else {
-      mainEl.classList.remove("fullscreen");
-    }
+    mainEl.classList.toggle("fullscreen", currentDisplayMode === "fullscreen");
   } catch (err) {
     log.error("Failed to change display mode:", err);
   }

src/app.examples.ts

@@ -206,6 +206,20 @@ function App_onhostcontextchanged_respondToTheme(app: App) {
   //#endregion App_onhostcontextchanged_respondToTheme
 }
 
+/**
+ * Example: Respond to display mode changes using onhostcontextchanged.
+ */
+function App_onhostcontextchanged_respondToDisplayMode(app: App) {
+  //#region App_onhostcontextchanged_respondToDisplayMode
+  app.onhostcontextchanged = (params) => {
+    if (params.displayMode) {
+      const isFullscreen = params.displayMode === "fullscreen";
+      document.body.classList.toggle("fullscreen", isFullscreen);
+    }
+  };
+  //#endregion App_onhostcontextchanged_respondToDisplayMode
+}
+
 /**
  * Example: Perform cleanup before teardown.
  */
@@ -344,16 +358,17 @@ async function App_openLink_documentation(app: App) {
 }
 
 /**
- * Example: Request fullscreen mode.
+ * Example: Toggle between inline and fullscreen display modes.
  */
-async function App_requestDisplayMode_fullscreen(app: App) {
-  //#region App_requestDisplayMode_fullscreen
-  const context = app.getHostContext();
-  if (context?.availableDisplayModes?.includes("fullscreen")) {
-    const result = await app.requestDisplayMode({ mode: "fullscreen" });
-    console.log("Display mode set to:", result.mode);
+async function App_requestDisplayMode_toggle(app: App) {
+  //#region App_requestDisplayMode_toggle
+  const ctx = app.getHostContext();
+  if (ctx?.availableDisplayModes?.includes("fullscreen")) {
+    const target = ctx.displayMode === "fullscreen" ? "inline" : "fullscreen";
+    const result = await app.requestDisplayMode({ mode: target });
+    console.log("Now in:", result.mode);
   }
-  //#endregion App_requestDisplayMode_fullscreen
+  //#endregion App_requestDisplayMode_toggle
 }
 
 /**

src/app.ts

@@ -729,8 +729,8 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
    * @param options - Request options (timeout, etc.)
    * @returns Result containing the actual display mode that was set
    *
-   * @example Request fullscreen mode
-   * {@includeCode ./app.examples.ts#App_requestDisplayMode_fullscreen}
+   * @example Toggle display mode
+   * {@includeCode ./app.examples.ts#App_requestDisplayMode_toggle}
    *
    * @see {@link McpUiRequestDisplayModeRequest} for request structure
    * @see {@link McpUiHostContext} for checking availableDisplayModes