Complete "Giving errors back to model" pattern documentation

Adds JSDoc example `App_updateModelContext_reportError` showing how to
report runtime errors (e.g., microphone permission denied) back to the
model using `updateModelContext`.

Updates patterns.md with clearer framing:
- Server-side (tool handler): return `{ isError: true, ... }`
- Client-side (app): use `updateModelContext` for runtime errors

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

src/app.examples.ts

@@ -364,6 +364,28 @@ async function App_updateModelContext_structuredContent(app: App) {
   //#endregion App_updateModelContext_structuredContent
 }
 
+/**
+ * Example: Report runtime error to model.
+ */
+async function App_updateModelContext_reportError(app: App) {
+  //#region App_updateModelContext_reportError
+  try {
+    const _stream = await navigator.mediaDevices.getUserMedia({ audio: true });
+    // ... use _stream for transcription
+  } catch (err) {
+    // Inform the model that the app is in a degraded state
+    await app.updateModelContext({
+      content: [
+        {
+          type: "text",
+          text: "Error: transcription unavailable",
+        },
+      ],
+    });
+  }
+  //#endregion App_updateModelContext_reportError
+}
+
 /**
  * Example: Open documentation link.
  */

src/app.ts

@@ -674,6 +674,9 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
    * @example Update with structured content
    * {@includeCode ./app.examples.ts#App_updateModelContext_structuredContent}
    *
+   * @example Report runtime error to model
+   * {@includeCode ./app.examples.ts#App_updateModelContext_reportError}
+   *
    * @returns Promise that resolves when the context update is acknowledged
    */
   updateModelContext(