compose: column/frame breaks re-flow the rest of the paragraph into the next column/frame; tab tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/compose/src/lib.rs

@@ -461,16 +461,25 @@ pub fn compose(doc: &Document, story: &Story, frames: &[FrameSpec], opts: &Compo
                 // Column / frame / page break characters.
                 if b.forced && e < glyphs.len() + 1 {
                     let brk = glyphs.get(g0 + b.next.saturating_sub(1)).map(|g| g.ch);
-                    match brk {
+                    let jumped = match brk {
                         Some(story::COLUMN_BREAK) => {
                             cur.next_column(&cols);
-                            col_first_line = line_no;
+                            true
                         }
                         Some(story::FRAME_BREAK) | Some(story::PAGE_BREAK) => {
                             cur.next_frame();
-                            col_first_line = line_no;
+                            true
+                        }
+                        _ => false,
+                    };
+                    if jumped {
+                        // The rest of the paragraph continues in the new column/frame: re-break it there.
+                        col_first_line = line_no;
+                        if k + 1 < breaks.len() {
+                            g0 += b.next;
+                            moved = true;
+                            break;
                         }
-                        _ => {}
                     }
                 }
             }

crates/compose/src/tests.rs

@@ -547,3 +547,25 @@ fn perf_compose_300k_story() {
         assert!(ms < 300.0, "composition took {ms:.1} ms");
     }
 }
+
+#[test]
+fn column_break_moves_following_text() {
+    let text = format!("First column text.{}Second column text.", designcraft_doc::story::COLUMN_BREAK);
+    let (mut d, sid, fid) = doc_with(&text, Rect::new(0.0, 0.0, 400.0, 300.0), ParaAttrs::default());
+    d.item_mut(fid).unwrap().text_frame_mut().unwrap().options.columns = 2;
+    let cs = compose_story(&d, sid, &ComposeOptions::default());
+    let lines = all_lines(&cs);
+    assert_eq!(lines.len(), 2, "{}", lines.len());
+    assert_eq!(lines[0].column, 0);
+    assert_eq!(lines[1].column, 1);
+    assert!(lines[1].baseline < 20.0, "second column starts at the top");
+}
+
+#[test]
+fn tabs_without_stops_use_default_half_inch() {
+    let (d, sid, _) = doc_with("A\tB", Rect::new(0.0, 0.0, 300.0, 100.0), ParaAttrs::default());
+    let cs = compose_story(&d, sid, &ComposeOptions::default());
+    let l = &cs.frames[0].lines[0];
+    let b = l.glyphs.iter().find(|g| g.byte == 2).expect("B");
+    assert!((b.x - 36.0).abs() < 0.5, "B at {}", b.x);
+}