fix: avoid indentation-only wrapped rows

The shared wrapper treated leading whitespace as a usable word boundary,
pushing a long first token onto a continuation and leaving a numbered blank row.
Only record boundaries after non-whitespace content on the current visual row.
Preserve source whitespace, tab stops, caret rows and paired diff alignment.

Verified: 945 tests, formatting, and live ordinary/split-diff fixture smoke,
including wrap off/on and aligned closing brackets.

src/wrap.rs

@@ -36,6 +36,7 @@ impl WrapCache {
             let mut start = 0;
             let mut column = 0;
             let mut word_boundary = 0;
+            let mut content_end = 0;
             for grapheme in text.graphemes(true) {
                 let cells = if grapheme == "\t" {
                     TAB_WIDTH - column % TAB_WIDTH
@@ -64,7 +65,10 @@ impl WrapCache {
                     }
                 }
                 column += cells;
-                if grapheme.chars().all(char::is_whitespace) {
+                if !grapheme.chars().all(char::is_whitespace) {
+                    content_end = column;
+                } else if content_end > start {
+                    // A word break must not leave only whitespace on this visual row.
                     word_boundary = column;
                 }
             }
@@ -116,6 +120,30 @@ mod tests {
         assert_eq!(caret_segment(&segments, 8), 2);
     }
 
+    #[test]
+    fn long_words_do_not_wrap_indentation_onto_an_empty_visual_row() {
+        for source in [
+            "    abcdefghijk",
+            "\tabcdefghijk",
+            "head          abcdefghijk",
+        ] {
+            let expanded = source.replace('\t', "    ");
+            let segments = layout(source, 8);
+            assert_eq!(segments.first().unwrap().start, 0);
+            assert_eq!(segments.last().unwrap().end, expanded.len());
+            assert!(segments.windows(2).all(|pair| pair[0].end == pair[1].start));
+            for segment in segments
+                .iter()
+                .filter(|segment| segment.start < segment.end)
+            {
+                assert!(
+                    !expanded[segment.start..segment.end].trim().is_empty(),
+                    "whitespace-only visual row {segment:?} in {source:?}"
+                );
+            }
+        }
+    }
+
     #[test]
     fn tabs_use_source_stops_and_unicode_graphemes_remain_intact() {
         assert_eq!(