fix(pdf-viewer): read live displayMode in requestFitToContent, guard tiny measurements

currentDisplayMode defaults to "inline" and handleHostContextChanged
only writes it `if (ctx.displayMode)`. If the host's initial context
omits the field — or the update lands one tick after a renderPage() —
requestFitToContent measures a near-empty pageWrapper and sends ~85px
(toolbar + padding only), shrinking a fullscreen iframe to a sliver.
Workaround was exit + re-enter fullscreen to force a context update.

Read app.getHostContext().displayMode directly (always fresh), and
separately refuse to send when pageWrapper measures smaller than the
toolbar — that's never a real layout, just an early render.

Author: ochafik

examples/pdf-server/src/mcp-app.ts

@@ -287,8 +287,14 @@ async function computeFitToWidthScale(): Promise<number | null> {
  * Only applies in inline mode - fullscreen mode uses scrolling.
  */
 function requestFitToContent() {
-  if (currentDisplayMode === "fullscreen") {
-    return; // Fullscreen uses scrolling
+  // Read the host's current state, not our cached currentDisplayMode.
+  // currentDisplayMode defaults to "inline" and handleHostContextChanged
+  // only updates it `if (ctx.displayMode)` — if the host omits the field
+  // or the update lands one tick late, the cached value lies. We've seen
+  // this measure a near-empty pageWrapper (~85px = toolbar + padding) and
+  // shrink a fullscreen iframe to a sliver.
+  if (app.getHostContext()?.displayMode === "fullscreen") {
+    return;
   }
 
   const canvasHeight = canvasEl.height;
@@ -324,6 +330,16 @@ function requestFitToContent() {
   // In inline mode (this function early-returns for fullscreen) the side panel is hidden
   const totalWidth = pageWrapperEl.offsetWidth + BUFFER;
 
+  // pageWrapper measuring ≈ 0 means the canvas hasn't laid out yet (early
+  // render, hidden ancestor, etc). Sending toolbar-height-only would shrink
+  // the iframe to a sliver. The next renderPage() will measure correctly.
+  if (pageWrapperHeight < toolbarHeight) {
+    log.info(
+      `requestFitToContent: pageWrapper ${pageWrapperHeight}px < toolbar ${toolbarHeight}px — skipping`,
+    );
+    return;
+  }
+
   app.sendSizeChanged({ width: totalWidth, height: totalHeight });
 }