Re-land bbiggs changes to reduce margin on narrow screens with fixes + full width setting (#10522)

packages/cli/src/ui/utils/ui-sizing.ts

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { lerp } from '../../utils/math.js';
+import { type LoadedSettings } from '../../config/settings.js';
+
+const getMainAreaWidthInternal = (terminalWidth: number): number => {
+  if (terminalWidth <= 80) {
+    return Math.round(0.98 * terminalWidth);
+  }
+  if (terminalWidth >= 132) {
+    return Math.round(0.9 * terminalWidth);
+  }
+
+  // Linearly interpolate between 80 columns (98%) and 132 columns (90%).
+  const t = (terminalWidth - 80) / (132 - 80);
+  const percentage = lerp(98, 90, t);
+
+  return Math.round(percentage * terminalWidth * 0.01);
+};
+
+export const calculateMainAreaWidth = (
+  terminalWidth: number,
+  settings: LoadedSettings,
+): number =>
+  settings.merged.ui?.useFullWidth
+    ? terminalWidth
+    : getMainAreaWidthInternal(terminalWidth);