Complete "Sending large follow-up messages" pattern documentation

Add new pattern showing how to combine `updateModelContext()` with
`sendMessage()` when data exceeds message size limits. The example
demonstrates offloading a large transcript to model context first,
then sending a brief trigger message.

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

docs/patterns.md

@@ -64,6 +64,12 @@ Use {@link app!App.updateModelContext updateModelContext} to keep the model info
 
 {@includeCode ../src/app.examples.ts#App_updateModelContext_appState}
 
+## Sending large follow-up messages
+
+When you need to send more data than fits in a message, use {@link app!App.updateModelContext updateModelContext} to set the context first, then {@link app!App.sendMessage sendMessage} with a brief prompt to trigger a response:
+
+{@includeCode ../src/app.examples.ts#App_sendMessage_withLargeContext}
+
 ## Persisting widget state
 
 To persist widget state across conversation reloads (e.g., current page in a PDF viewer, camera position in a map), use [`localStorage`](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage) with a stable identifier provided by the server.

src/app.examples.ts

@@ -81,18 +81,6 @@ async function App_basicUsage() {
   //#endregion App_basicUsage
 }
 
-/**
- * Example: Sending a message to the host's chat.
- */
-async function App_sendMessage(app: App) {
-  //#region App_sendMessage
-  await app.sendMessage({
-    role: "user",
-    content: [{ type: "text", text: "Weather updated!" }],
-  });
-  //#endregion App_sendMessage
-}
-
 /**
  * Example: Check host capabilities after connection.
  */
@@ -329,6 +317,33 @@ async function App_sendMessage_textFromInteraction(app: App) {
   //#endregion App_sendMessage_textFromInteraction
 }
 
+/**
+ * Example: Send follow-up message after offloading large data to model context.
+ */
+async function App_sendMessage_withLargeContext(
+  app: App,
+  fullTranscript: string,
+  speakerNames: string[],
+) {
+  //#region App_sendMessage_withLargeContext
+  const markdown = `---
+word-count: ${fullTranscript.split(/\s+/).length}
+speaker-names: ${speakerNames.join(", ")}
+---
+
+${fullTranscript}`;
+
+  // Offload long transcript to model context
+  await app.updateModelContext({ content: [{ type: "text", text: markdown }] });
+
+  // Send brief trigger message
+  await app.sendMessage({
+    role: "user",
+    content: [{ type: "text", text: "Summarize the key points" }],
+  });
+  //#endregion App_sendMessage_withLargeContext
+}
+
 /**
  * Example: Log app state for debugging.
  */

src/app.ts

@@ -156,9 +156,6 @@ type RequestHandlerExtra = Parameters<
  *
  * @example Basic usage with PostMessageTransport
  * {@includeCode ./app.examples.ts#App_basicUsage}
- *
- * @example Sending a message to the host's chat
- * {@includeCode ./app.examples.ts#App_sendMessage}
  */
 export class App extends Protocol<AppRequest, AppNotification, AppResult> {
   private _hostCapabilities?: McpUiHostCapabilities;
@@ -618,6 +615,9 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
    * @example Send a text message from user interaction
    * {@includeCode ./app.examples.ts#App_sendMessage_textFromInteraction}
    *
+   * @example Send follow-up message after offloading large data to model context
+   * {@includeCode ./app.examples.ts#App_sendMessage_withLargeContext}
+   *
    * @see {@link McpUiMessageRequest} for request structure
    */
   sendMessage(params: McpUiMessageRequest["params"], options?: RequestOptions) {