fix(runtime): call onRender before frame writes

Co-authored-by: Claude <noreply@anthropic.com>

packages/runtime-tests/integration/lifecycle/on-render.test.tsx

@@ -111,6 +111,58 @@ test("no onRender callback when option is not provided", async () => {
   app.unmount();
 });
 
+async function expectOnRenderWriteBeforeFrame(
+  options: {
+    debug?: boolean;
+    isScreenReaderEnabled?: boolean;
+  } = {},
+) {
+  const App = defineComponent(() => () => <Text>Hello</Text>);
+
+  const app = createApp(App);
+  const stdout = makeFakeWritable({ columns: 80 });
+  const stderr = makeFakeWritable({ columns: 80 });
+  const { stream: stdin } = makeFakeStdin();
+
+  const writes: string[] = [];
+  (stdout as unknown as PassThrough).on("data", (chunk: Buffer) => {
+    writes.push(chunk.toString());
+  });
+
+  app.mount({
+    stdout,
+    stdin,
+    stderr,
+    exitOnCtrlC: false,
+    ...options,
+    onRender: () => {
+      stdout.write("R");
+    },
+  });
+
+  await nextTick();
+  await nextTick();
+
+  const output = writes.join("");
+  expect(output.indexOf("R")).toBeGreaterThanOrEqual(0);
+  expect(output.indexOf("Hello")).toBeGreaterThanOrEqual(0);
+  expect(output.indexOf("R")).toBeLessThan(output.indexOf("Hello"));
+
+  app.unmount();
+}
+
+test("onRender fires before debug output is written", async () => {
+  await expectOnRenderWriteBeforeFrame({ debug: true });
+});
+
+test("onRender fires before interactive output is written", async () => {
+  await expectOnRenderWriteBeforeFrame();
+});
+
+test("onRender fires before screen-reader output is written", async () => {
+  await expectOnRenderWriteBeforeFrame({ isScreenReaderEnabled: true });
+});
+
 test("onRender fires on input-triggered state update", async () => {
   // Mirrors the third assertion in Ink's "outputs renderTime when onRender is passed":
   // after an initial render and a manual rerender, a useInput-driven state

packages/runtime/src/render.ts

@@ -916,11 +916,8 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
       }
 
       if (!interactive && !debug) {
-        // Non-interactive: write static output immediately, defer dynamic frame.
+        // Non-interactive: compute the dynamic frame now, write static output
-        if (hasStaticOutput) {
+        // after onRender, and defer dynamic frame output until unmount.
-          stdout.write(staticOutput);
-        }
-
         tuiRoot.yoga.setWidth(w);
         tuiRoot.yoga.calculateLayout(w, undefined, Yoga.DIRECTION_LTR);
         emitLayoutListeners(tuiRoot);
@@ -929,6 +926,9 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         frameState.lastOutputToRender = frame + "\n";
         frameState.outputHeight = frame === "" ? 0 : frame.split("\n").length;
         if (onRender) onRender({ renderTime: performance.now() - start });
+        if (hasStaticOutput) {
+          stdout.write(staticOutput);
+        }
         return;
       }
 
@@ -978,6 +978,7 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         frameState.lastOutput = frame;
         frameState.lastOutputToRender = frame;
         frameState.outputHeight = outputHeight;
+        if (onRender) onRender({ renderTime: performance.now() - start });
         // Ink writes `fullStaticOutput + output` with NO trailing newline
         // (ink.tsx:558; `output` is \n-joined and returned WITHOUT a trailing
         // \n — output.ts:305-312). Writing `frame` (not `frame + "\n"`) makes
@@ -991,7 +992,6 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         // flushes to stdout for byte parity but is not a render, so it must not
         // append a duplicate of the final frame to the live frames[].
         if (!teardownStarted) frameSink?.(frame);
-        if (onRender) onRender({ renderTime: performance.now() - start });
         return;
       }
 
@@ -1009,6 +1009,7 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         // `frame` is already the wrapped SR output (renderFrame -> wrapAnsi), so
         // it plays the role of Ink's `wrappedOutput`.
         const sync = synchronize;
+        if (onRender) onRender({ renderTime: performance.now() - start });
         if (sync) stdout.write(bsu);
 
         if (hasStaticOutput) {
@@ -1023,7 +1024,6 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         if (frame === frameState.lastOutput && !hasStaticOutput) {
           // Unchanged frame and no new static: nothing to write (ink.tsx:590-596).
           if (sync) stdout.write(esu);
-          if (onRender) onRender({ renderTime: performance.now() - start });
           return;
         }
 
@@ -1044,13 +1044,12 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
         frameState.outputHeight = frame === "" ? 0 : frame.split("\n").length;
 
         if (sync) stdout.write(esu);
-        if (onRender) onRender({ renderTime: performance.now() - start });
         return;
       }
 
       // Interactive path
-      renderInteractiveFrame(frame, outputHeight, hasStaticOutput ? staticOutput : "");
       if (onRender) onRender({ renderTime: performance.now() - start });
+      renderInteractiveFrame(frame, outputHeight, hasStaticOutput ? staticOutput : "");
     }
 
     // A single render-throttle window derived from maxFps drives BOTH the