Complete "Lowering perceived latency" pattern documentation

- Expand `App_ontoolinputpartial_progressiveRendering` example in
  `app.examples.ts` to show full state management pattern with
  `toolInputs` and `toolInputsPartial` variables
- Add healed JSON caveat to `ontoolinputpartial` JSDoc in `app.ts`
- Update `patterns.md` to reference the expanded example and document
  the streaming preview pattern
- Remove empty `lowerPerceivedLatency` placeholder from `patterns.tsx`

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

docs/patterns.md

@@ -60,13 +60,14 @@ Listen for display mode changes via {@link app!App.onhostcontextchanged onhostco
 
 {@includeCode ./patterns.tsx#persistData}
 
-## [TODO] Lower perceived latency / manage loading time
+## Lowering perceived latency
 
-Leverage partial inputs to show widgets as possible.
+Use {@link app!App.ontoolinputpartial ontoolinputpartial} to receive streaming tool arguments as they arrive, allowing you to show a loading preview before the complete input is available.
 
-Beware of partial JSON being partial (but healed), so some of your objects may not be complete (e.g. in a list you may need to skip the last item if your code validates input schemas strictly).
+{@includeCode ../src/app.examples.ts#App_ontoolinputpartial_progressiveRendering}
 
-{@includeCode ./patterns.tsx#lowerPerceivedLatency}
+> [!IMPORTANT]
+> Partial arguments are "healed" JSON — the host closes unclosed brackets/braces to produce valid JSON. This means objects may be incomplete (e.g., the last item in an array may be truncated). Don't rely on partial data for critical operations; use it only for preview UI.
 
 ## [TODO] Supporting both iframe & MCP Apps in same binary
 

docs/patterns.tsx

@@ -111,17 +111,6 @@ function persistData(app: App) {
   //#endregion persistData
 }
 
-/**
- * Example: Lower perceived latency / manage loading time
- */
-function lowerPerceivedLatency(app: App) {
-  //#region lowerPerceivedLatency
-  // TODO: Leverage partial inputs to show widgets as possible.
-  // Beware of partial JSON being partial (but healed),
-  // so some objects may not be complete.
-  //#endregion lowerPerceivedLatency
-}
-
 /**
  * Example: Supporting both iframe & MCP Apps in same binary
  */
@@ -147,6 +136,5 @@ void errorsToModel;
 void hostStylingVanillaJs;
 void hostStylingReact;
 void persistData;
-void lowerPerceivedLatency;
 void iframeAndMcpApps;
 void migrateFromOpenai;

src/app.examples.ts

@@ -157,13 +157,34 @@ async function App_ontoolinput_setter(app: App) {
  */
 function App_ontoolinputpartial_progressiveRendering(app: App) {
   //#region App_ontoolinputpartial_progressiveRendering
+  let toolInputs: Record<string, unknown> | null = null;
+  let toolInputsPartial: Record<string, unknown> | null = null;
+
   app.ontoolinputpartial = (params) => {
-    console.log("Partial args:", params.arguments);
-    // Update your UI progressively as arguments stream in
+    toolInputsPartial = params.arguments as Record<string, unknown>;
+    render();
   };
+
+  app.ontoolinput = (params) => {
+    toolInputs = params.arguments as Record<string, unknown>;
+    toolInputsPartial = null;
+    render();
+  };
+
+  function render() {
+    if (toolInputs) {
+      renderFinalUI(toolInputs);
+    } else {
+      renderLoadingUI(toolInputsPartial); // e.g., shimmer with partial preview
+    }
+  }
   //#endregion App_ontoolinputpartial_progressiveRendering
 }
 
+// Stubs for App_ontoolinputpartial_progressiveRendering example
+declare function renderLoadingUI(data: Record<string, unknown> | null): void;
+declare function renderFinalUI(data: Record<string, unknown>): void;
+
 /**
  * Example: Display tool execution results using ontoolresult.
  */

src/app.ts

@@ -287,6 +287,11 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
    * streams partial tool arguments during tool call initialization. This enables
    * progressive rendering of tool arguments before they're complete.
    *
+   * **Important:** Partial arguments are "healed" JSON — the host closes unclosed
+   * brackets/braces to produce valid JSON. This means objects may be incomplete
+   * (e.g., the last item in an array may be truncated). Use partial data only
+   * for preview UI, not for critical operations.
+   *
    * This setter is a convenience wrapper around `setNotificationHandler()` that
    * automatically handles the notification schema and extracts the params for you.
    *