1  import { stringWidth } from './stringWidth.js'
 2  
 3  // During streaming, text grows but completed lines are immutable.
 4  // Caching stringWidth per-line avoids re-measuring hundreds of
 5  // unchanged lines on every token (~50x reduction in stringWidth calls).
 6  const cache = new Map<string, number>()
 7  
 8  const MAX_CACHE_SIZE = 4096
 9  
10  export function lineWidth(line: string): number {
11    const cached = cache.get(line)
12    if (cached !== undefined) return cached
13  
14    const width = stringWidth(line)
15  
16    // Evict when cache grows too large (e.g. after many different responses).
17    // Simple full-clear is fine — the cache repopulates in one frame.
18    if (cache.size >= MAX_CACHE_SIZE) {
19      cache.clear()
20    }
21  
22    cache.set(line, width)
23    return width
24  }