fix: InputPrompt wrapped lines maintain highlighting, increase responsiveness in narrow cases (#7656)

Co-authored-by: Jacob Richman <jacob314@gmail.com>
Co-authored-by: Arya Gummadi <aryagummadi@google.com>

packages/cli/src/ui/utils/highlight.ts

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import { cpLen, cpSlice } from './textUtils.js';
+
 export type HighlightToken = {
   text: string;
   type: 'default' | 'command' | 'file';
@@ -63,3 +65,39 @@ export function parseInputForHighlighting(
 
   return tokens;
 }
+
+export function buildSegmentsForVisualSlice(
+  tokens: readonly HighlightToken[],
+  sliceStart: number,
+  sliceEnd: number,
+): readonly HighlightToken[] {
+  if (sliceStart >= sliceEnd) return [];
+
+  const segments: HighlightToken[] = [];
+  let tokenCpStart = 0;
+
+  for (const token of tokens) {
+    const tokenLen = cpLen(token.text);
+    const tokenStart = tokenCpStart;
+    const tokenEnd = tokenStart + tokenLen;
+
+    const overlapStart = Math.max(tokenStart, sliceStart);
+    const overlapEnd = Math.min(tokenEnd, sliceEnd);
+    if (overlapStart < overlapEnd) {
+      const sliceStartInToken = overlapStart - tokenStart;
+      const sliceEndInToken = overlapEnd - tokenStart;
+      const rawSlice = cpSlice(token.text, sliceStartInToken, sliceEndInToken);
+
+      const last = segments[segments.length - 1];
+      if (last && last.type === token.type) {
+        last.text += rawSlice;
+      } else {
+        segments.push({ type: token.type, text: rawSlice });
+      }
+    }
+
+    tokenCpStart += tokenLen;
+  }
+
+  return segments;
+}