fix(markdown): address code review findings — updateItem, height measurement, CSS injection, paste fallback, resize sprite update

frontend/src/canvas/MarkdownOverlay.ts

@@ -126,7 +126,8 @@ export class MarkdownOverlay {
     if (!entry || !item || item.type !== 'markdown') return;
 
     requestAnimationFrame(() => {
-      const h = entry.el.offsetHeight / this._viewport.scale.x;
+      // offsetHeight is the CSS layout height at unscaled width — already in world space
+      const h = entry.el.offsetHeight;
       if (Math.abs(h - item.data.h) > 1) {
         item.data.h = h;
         // Redraw MarkdownSprite background

frontend/src/canvas/SceneManager.ts

@@ -465,6 +465,9 @@ export class SceneManager {
       const imgData = data as ImageObject;
       obj.applyCrop(imgData.crop);
     }
+    if (data.type === 'markdown' && obj instanceof MarkdownSprite) {
+      obj.updateFromData(data as MarkdownObject);
+    }
 
     // Update stored data
     item.data = { ...data };

frontend/src/canvas/TransformBox.ts

@@ -8,6 +8,8 @@
 
 import { Container, Graphics, FederatedPointerEvent, Text, TextStyle } from 'pixi.js';
 import type { Viewport } from 'pixi-viewport';
+import { MarkdownSprite } from './sprites/MarkdownSprite';
+import type { MarkdownObject } from './scene-format';
 import { type SceneItem, getItemWorldBounds } from './SceneManager';
 import type { SnapGuides } from './SnapGuides';
 import { applyImageDisplayTransform } from './imageTransforms';
@@ -360,6 +362,9 @@ export class TransformBox extends Container {
         item.data.x = orig.x;
         item.data.y = orig.y;
         item.displayObject.position.set(item.data.x, item.data.y);
+        if (item.displayObject instanceof MarkdownSprite) {
+          item.displayObject.updateFromData(item.data as MarkdownObject);
+        }
         this._onItemTransform?.(item);
         continue; // Skip normal sx/sy scaling
       }

frontend/src/canvas/image-drop.ts

@@ -346,13 +346,16 @@ export function setupPaste(
     }
 
     if (textContent) {
-      e.preventDefault();
-      if (textContent.length > 20) {
-        opts?.onTextPaste?.({ text: textContent, html: htmlContent, hasImage: hasMedia });
-      } else {
-        opts?.onShortTextPaste?.(textContent);
+      if (textContent.length > 20 && opts?.onTextPaste) {
+        e.preventDefault();
+        opts.onTextPaste({ text: textContent, html: htmlContent, hasImage: hasMedia });
+        return;
+      } else if (textContent.length <= 20 && opts?.onShortTextPaste) {
+        e.preventDefault();
+        opts.onShortTextPaste(textContent);
+        return;
       }
-      return;
+      // No callback provided — let native paste behavior through
     }
 
     // ── Media paste logic (unchanged) ──