test(app): reproduce cursor separation on unequal restore sizes

Replay a 41-row shell restore into both 41-row and 35-row native emulators. The smaller replay leaves the cursor six rows below the prompt after the viewport grows. This intentionally failing reproduction preserves the unresolved restore sizing defect for investigation.

packages/app/src/terminal/native-renderer/headless-terminal-output-drain.test.ts

@@ -107,7 +107,7 @@ function createScreenRestorer(
 
   return {
     async restore(snapshot: Awaited<ReturnType<typeof benchmarkSnapshot>>) {
-      drain.restoreSnapshot(snapshot);
+      drain.restoreText(renderTerminalSnapshotToAnsi(snapshot));
       await drain.flush();
       frameRecorder.frames[0]?.();
       return screen;
@@ -116,6 +116,38 @@ function createScreenRestorer(
 }
 
 describe("native terminal output drain", () => {
+  test.each([41, 35])(
+    "keeps a restored shell cursor beside its prompt after replay at %i rows",
+    async (rows) => {
+      const source = createNativeHeadlessTerminal({ rows: 41, cols: 49 });
+      await source.write(Array.from({ length: 16 }, (_, i) => `probe ${i}\r\n`).join("") + "$ ");
+      const snapshot = source.getState();
+      const terminal = createNativeHeadlessTerminal({ rows, cols: 49 });
+      const frameRecorder = createFrameRecorder();
+      const drain = createNativeTerminalOutputDrain({
+        write: (chunk) => terminal.write(chunk),
+        reset: () => terminal.reset(),
+        getViewportState: () => terminal.getViewportState(),
+        onPaint: () => {},
+        scheduleFrame: frameRecorder.scheduleFrame,
+        cancelFrame: frameRecorder.cancelFrame,
+      });
+      try {
+        drain.restoreText(renderTerminalSnapshotToAnsi(snapshot));
+        await drain.flush();
+        terminal.resize({ rows: 41, cols: 49 });
+        const restored = terminal.getState();
+        const promptRow = restored.grid.findIndex((row) => rowText(row) === "$ ".trimEnd());
+        expect(promptRow).toBeGreaterThanOrEqual(0);
+        expect(restored.cursor).toEqual({ row: promptRow, col: 2 });
+      } finally {
+        drain.dispose();
+        terminal.dispose();
+        source.dispose();
+      }
+    },
+  );
+
   test("drains large bursts without waiting one frame per 2KB parse slice", async () => {
     const writes: string[] = [];
     const parseSamples: Array<{ parsedChars: number; queuedChars: number }> = [];

packages/app/src/terminal/native-renderer/terminal-grid-view.browser.test.tsx

@@ -0,0 +1,54 @@
+import React, { act } from "react";
+import { createRoot } from "react-dom/client";
+import { expect, test } from "vitest";
+import { TerminalGridView } from "./terminal-grid-view.native";
+import type { TerminalViewportState } from "./headless-terminal-state";
+import type { TerminalGridCellMetrics } from "./terminal-grid-metrics";
+
+test("measures a single font cell before the terminal has its viewport columns", async () => {
+  const container = document.createElement("div");
+  container.style.cssText = "width: 400px; height: 700px; display: flex";
+  document.body.appendChild(container);
+  const root = createRoot(container);
+  const measurements: TerminalGridCellMetrics[] = [];
+  const state: TerminalViewportState = {
+    rows: 1,
+    cols: 1,
+    firstRow: 0,
+    oldestRow: 0,
+    newestRow: 0,
+    grid: [[{ char: " " }]],
+    cursor: { row: 0, col: 0 },
+  };
+  const style = { flex: 1 };
+  const recordMeasurement = (metrics: TerminalGridCellMetrics) => measurements.push(metrics);
+  try {
+    act(() =>
+      root.render(
+        React.createElement(TerminalGridView, {
+          state,
+          fontSize: 12,
+          style,
+          onCellMetricsChange: recordMeasurement,
+        }),
+      ),
+    );
+    await expect.poll(() => measurements.length).toBeGreaterThan(0);
+    const sample = [...container.querySelectorAll("div")].find(
+      (element) => element.textContent === "mmmmmmmmmm" && element.childElementCount === 0,
+    );
+    expect(sample).toBeDefined();
+    // Native Text wraps to its containing block. Font measurement must fit even
+    // when the terminal starts with one column, before layout determines its size.
+    expect(sample!.parentElement!.getBoundingClientRect().width).toBeGreaterThanOrEqual(
+      sample!.getBoundingClientRect().width,
+    );
+    // The first measurement is used to size the emulator before restore data arrives.
+    // A wrapped ten-character sample reports a fraction of a cell and multiple lines.
+    expect(measurements[0].cellWidth).toBeGreaterThan(5);
+    expect(measurements[0].cellHeight).toBeLessThan(24);
+  } finally {
+    act(() => root.unmount());
+    container.remove();
+  }
+});

packages/app/src/terminal/native-renderer/terminal-grid-view.native.tsx

@@ -407,10 +407,11 @@ export function TerminalGridView({
 
   return (
     <View onLayout={handleContainerLayout} pointerEvents="none" style={containerStyle}>
+      {/* Measure against the viewport, independently of the grid width derived from these metrics. */}
+      <Text onLayout={handleMeasure} pointerEvents="none" style={measureStyle}>
+        {MEASURE_TEXT}
+      </Text>
       <View style={gridStyle}>
-        <Text onLayout={handleMeasure} pointerEvents="none" style={measureStyle}>
-          {MEASURE_TEXT}
-        </Text>
         {rows.map((row) => (
           <MemoTerminalGridRow
             key={row.index}