fix(streamdown): re-render memoized components when node offset changes

.changeset/fair-balloons-share.md

@@ -0,0 +1,5 @@
+---
+"streamdown": patch
+---
+
+Fix stale rendering when in-block markdown content changes during streaming updates.

packages/streamdown/__tests__/components-rerender.test.tsx

@@ -422,6 +422,39 @@ describe("sameNodePosition edge cases", () => {
 
     expect(container.querySelector("ol")).toBeTruthy();
   });
+
+  it("should re-render when only offset changes", () => {
+    const nodeV1 = {
+      position: {
+        start: { line: 1, column: 1, offset: 0 },
+        end: { line: 2, column: 5, offset: 20 },
+      },
+    };
+    const nodeV2 = {
+      position: {
+        start: { line: 1, column: 1, offset: 0 },
+        end: { line: 2, column: 5, offset: 35 },
+      },
+    };
+
+    const { container, rerender } = render(
+      <ReRenderWrapper count={0}>
+        <Ol node={nodeV1 as any}>
+          <li>item</li>
+        </Ol>
+      </ReRenderWrapper>
+    );
+
+    rerender(
+      <ReRenderWrapper count={1}>
+        <Ol node={nodeV2 as any}>
+          <li>item</li>
+        </Ol>
+      </ReRenderWrapper>
+    );
+
+    expect(container.querySelector("ol")).toBeTruthy();
+  });
 });
 
 describe("MemoParagraph block code unwrapping with data-block", () => {

packages/streamdown/lib/components.tsx

@@ -42,6 +42,7 @@ const LANGUAGE_REGEX = /language-([^\s]+)/;
 interface MarkdownPoint {
   column?: number;
   line?: number;
+  offset?: number;
 }
 interface MarkdownPosition {
   end?: MarkdownPoint;
@@ -74,8 +75,10 @@ function sameNodePosition(prev?: MarkdownNode, next?: MarkdownNode): boolean {
   return (
     prevStart?.line === nextStart?.line &&
     prevStart?.column === nextStart?.column &&
+    prevStart?.offset === nextStart?.offset &&
     prevEnd?.line === nextEnd?.line &&
-    prevEnd?.column === nextEnd?.column
+    prevEnd?.column === nextEnd?.column &&
+    prevEnd?.offset === nextEnd?.offset
   );
 }