fix(transient-render-engine): preserve nested inline boundary spaces

Keep boundary spaces inside named inline wrappers until the parent
phrasing node collapses sibling whitespace.

Add a regression test for nested inline tags that previously rendered
"foobar" instead of "foo bar".

Made-with: Cursor

Author: leineveber

packages/transient-render-engine/src/flow/__tests__/collapse.test.ts

@@ -37,6 +37,19 @@ describe('collapse function', () => {
     const ttree = makeTTree('<span><span>foo </span><span> bar</span></span>');
     expect(ttree).toMatchSnapshot();
   });
+  it('should preserve boundary spaces wrapped in nested inline phrasing tags', () => {
+    const ttree = makeTTree(
+      '<span><span><strong>foo</strong> </span><span><strong>bar</strong></span></span>'
+    );
+    const [firstSpan, secondSpan] = ttree.children;
+    expect(firstSpan.tagName).toBe('span');
+    expect(firstSpan.children).toHaveLength(2);
+    expect((firstSpan.children[0] as TTextImpl).data).toBe('foo');
+    expect((firstSpan.children[1] as TTextImpl).data).toBe(' ');
+    expect(secondSpan.tagName).toBe('span');
+    expect(secondSpan.children).toHaveLength(1);
+    expect((secondSpan.children[0] as TTextImpl).data).toBe('bar');
+  });
   it('should handle nested anchors', () => {
     const ttree = makeTTree(nestedHyperlinksSource);
     expect(ttree).toMatchSnapshot();

packages/transient-render-engine/src/tree/TPhrasingCtor.ts

@@ -48,8 +48,12 @@ TPhrasingCtor.prototype.collapseChildren = function collapseChildren() {
     }
     previous = childK;
   });
-  this.trimLeft();
-  this.trimRight();
+  // Preserve boundary spaces for named inline wrappers (e.g. styled spans) so
+  // their parent phrasing container can collapse sibling boundaries correctly.
+  if (this.tagName === null) {
+    this.trimLeft();
+    this.trimRight();
+  }
   return null;
 };