SD-2570 - fix: document API tracked changes not fully rendered on document

packages/layout-engine/painters/dom/src/index.test.ts

@@ -10920,6 +10920,87 @@ describe('applyRunDataAttributes', () => {
       }).not.toThrow();
     });
 
+    it('renders all lines when measure indices come from inline-newline expansion', () => {
+      const inlineNewlineBlock: FlowBlock = {
+        kind: 'paragraph',
+        id: 'inline-newline-slice',
+        runs: [{ text: 'first\nsecond\nthird', fontFamily: 'Arial', fontSize: 16, pmStart: 0, pmEnd: 18 }],
+      };
+
+      // Measurer expands inline '\n' into: text, break, text, break, text.
+      const inlineNewlineMeasure: ParagraphMeasure = {
+        kind: 'paragraph',
+        lines: [
+          {
+            fromRun: 0,
+            fromChar: 0,
+            toRun: 0,
+            toChar: 5,
+            width: 40,
+            ascent: 12,
+            descent: 4,
+            lineHeight: 20,
+          },
+          {
+            fromRun: 2,
+            fromChar: 0,
+            toRun: 2,
+            toChar: 6,
+            width: 50,
+            ascent: 12,
+            descent: 4,
+            lineHeight: 20,
+          },
+          {
+            fromRun: 4,
+            fromChar: 0,
+            toRun: 4,
+            toChar: 5,
+            width: 40,
+            ascent: 12,
+            descent: 4,
+            lineHeight: 20,
+          },
+        ],
+        totalHeight: 60,
+      };
+
+      const inlineNewlineLayout: Layout = {
+        pageSize: { w: 400, h: 500 },
+        pages: [
+          {
+            number: 1,
+            fragments: [
+              {
+                kind: 'para',
+                blockId: 'inline-newline-slice',
+                fromLine: 0,
+                toLine: 3,
+                x: 20,
+                y: 20,
+                width: 300,
+              },
+            ],
+          },
+        ],
+      };
+
+      const painter = createTestPainter({
+        blocks: [inlineNewlineBlock],
+        measures: [inlineNewlineMeasure],
+      });
+
+      expect(() => {
+        painter.paint(inlineNewlineLayout, mount);
+      }).not.toThrow();
+
+      const fragment = mount.querySelector('.superdoc-fragment') as HTMLElement;
+      expect(fragment).toBeTruthy();
+      expect(fragment.textContent).toContain('first');
+      expect(fragment.textContent).toContain('second');
+      expect(fragment.textContent).toContain('third');
+    });
+
     it('preserves PM positions for lineBreak runs', () => {
       const lineBreakBlock: FlowBlock = {
         kind: 'paragraph',

packages/layout-engine/painters/dom/src/renderer.ts

@@ -7696,11 +7696,50 @@ const stripListIndent = (attrs?: ParagraphAttrs): ParagraphAttrs | undefined =>
  * // Returns runs or run slices that fall within the specified character range
  * ```
  */
+const expandRunsForInlineNewlines = (runs: Run[]): Run[] => {
+  const expanded: Run[] = [];
+
+  for (const run of runs) {
+    if ((run as TextRun).text && typeof (run as TextRun).text === 'string' && (run as TextRun).text.includes('\n')) {
+      const textRun = run as TextRun;
+      const segments = textRun.text.split('\n');
+      let cursor = textRun.pmStart ?? 0;
+
+      segments.forEach((segment, idx) => {
+        expanded.push({
+          ...textRun,
+          text: segment,
+          pmStart: cursor,
+          pmEnd: cursor + segment.length,
+        });
+        cursor += segment.length;
+
+        if (idx !== segments.length - 1) {
+          expanded.push({
+            kind: 'break',
+            breakType: 'line',
+            pmStart: cursor,
+            pmEnd: cursor + 1,
+            sdt: textRun.sdt,
+          });
+          cursor += 1;
+        }
+      });
+      continue;
+    }
+
+    expanded.push(run);
+  }
+
+  return expanded;
+};
+
 export const sliceRunsForLine = (block: ParagraphBlock, line: Line): Run[] => {
+  const runs = expandRunsForInlineNewlines(block.runs as Run[]);
   const result: Run[] = [];
 
   for (let runIndex = line.fromRun; runIndex <= line.toRun; runIndex += 1) {
-    const run = block.runs[runIndex];
+    const run = runs[runIndex];
     if (!run) continue;
 
     // FIXED: ImageRun handling - images are atomic units, no slicing needed