Fix autoResize reporting viewport height when content is taller (#525)

mel-anthropic · web-flow · commit 26928b862203 · 2026-03-06T13:30:13.000Z
fit-content clamps to the containing block's available size. For &lt;html&gt;,
that's the iframe viewport, so when content exceeds the viewport height
the SDK reported the viewport height instead of the true content height,
causing internal scrolling instead of iframe growth.

max-content has no available-space constraint and correctly reports the
intrinsic content height in both directions (shrink and grow). Width
stays fit-content to preserve responsive wrapping.
diff --git a/src/app.ts b/src/app.ts
@@ -1119,13 +1119,14 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
         scheduled = false;
         const html = document.documentElement;
 
-        // Measure actual content size by temporarily setting html to fit-content.
-        // This shrinks html to fit body (including body margins), giving us the
-        // true minimum size needed by the content.
+        // Measure actual content size by temporarily overriding html sizing.
+        // Width uses fit-content so content wraps at the host-provided width.
+        // Height uses max-content because fit-content would clamp to the viewport
+        // height when content is taller than the iframe, causing internal scrolling.
         const originalWidth = html.style.width;
         const originalHeight = html.style.height;
         html.style.width = "fit-content";
-        html.style.height = "fit-content";
+        html.style.height = "max-content";
         const rect = html.getBoundingClientRect();
         html.style.width = originalWidth;
         html.style.height = originalHeight;
