fix: the result preview truncates at the last word boundary

UI-SPEC E-1: a title or description wider than its pixel budget is cut
at the last word boundary that fits, then " …" is appended. The preview
cut inside a word and appended "…" without a space. A first word too
wide on its own is still cut inside the word. Bundle rebuilt.

assets/src/elements/measure.ts

@@ -62,23 +62,53 @@ export function textWidth(text: string, font: string): number {
   return estimate(text, size)
 }
 
-/** text cut to fit maxPx with an ellipsis, or text itself when it fits. */
+/** The mark appended to a truncated preview line (UI-SPEC E-1). */
+export const ELLIPSIS = ' …'
+
+/**
+ * text cut at the last word boundary that fits maxPx, then ELLIPSIS, or
+ * text itself when it fits (UI-SPEC E-1). A first word too wide on its own
+ * is cut inside the word.
+ */
 export function truncate(text: string, font: string, maxPx: number): string {
   if (textWidth(text, font) <= maxPx) {
     return text
   }
+  const fits = (s: string): boolean => textWidth(s + ELLIPSIS, font) <= maxPx
   const chars = Array.from(text)
+  // The word ends: where a run of spaces starts after a word.
+  const ends: number[] = []
+  for (let i = 1; i < chars.length; i++) {
+    if (/\s/u.test(chars[i]) && !/\s/u.test(chars[i - 1])) {
+      ends.push(i)
+    }
+  }
+  let best = -1
   let lo = 0
-  let hi = chars.length
-  while (lo < hi) {
-    const mid = Math.ceil((lo + hi) / 2)
-    if (textWidth(chars.slice(0, mid).join('').trimEnd() + '…', font) <= maxPx) {
-      lo = mid
+  let hi = ends.length - 1
+  while (lo <= hi) {
+    const mid = (lo + hi) >> 1
+    if (fits(chars.slice(0, ends[mid]).join(''))) {
+      best = mid
+      lo = mid + 1
     } else {
       hi = mid - 1
     }
   }
-  return chars.slice(0, lo).join('').trimEnd() + '…'
+  if (best >= 0) {
+    return chars.slice(0, ends[best]).join('') + ELLIPSIS
+  }
+  let cut = 0
+  let top = chars.length
+  while (cut < top) {
+    const mid = Math.ceil((cut + top) / 2)
+    if (fits(chars.slice(0, mid).join('').trimEnd())) {
+      cut = mid
+    } else {
+      top = mid - 1
+    }
+  }
+  return chars.slice(0, cut).join('').trimEnd() + ELLIPSIS
 }
 
 /** The font and pixel limit of a measured field. */