perf(sticky): remove creation delay + add dirty-checking to StickySprite

- Replace 50ms setTimeout with queueMicrotask for editor open
- Skip updateFromData() entirely when no inputs changed
- Cache background redraw inputs, skip Graphics clear+redraw when shape unchanged
- Separate text-only, style-only, and bg-only update paths

frontend/src/canvas/sprites/StickySprite.ts

@@ -10,6 +10,11 @@
  *   - width is fixed (from data.w)
  *   - height auto-grows to fit wrapped text + padding
  *   - parent SceneItem.data.h is updated after layout
+ *
+ * Performance:
+ *   - updateFromData() skips work when inputs haven't changed
+ *   - _drawBg() is cached and only redraws when dimensions/color change
+ *   - showText() never triggers layout or redraw
  */
 
 import { Container, Graphics, Text, TextStyle } from 'pixi.js';
@@ -32,6 +37,19 @@ export class StickySprite extends Container {
   private _cornerRadius = DEFAULT_CORNER_RADIUS;
   private _bgColor = '#ffd43b';
 
+  // Dirty-check cache: last known inputs to avoid redundant work
+  private _lastText = '';
+  private _lastFontSize = 14;
+  private _lastFontFamily = 'Inter, system-ui, sans-serif';
+  private _lastTextColor = '#1a1a1a';
+  private _lastFill = '#ffd43b';
+  private _lastW = 200;
+  private _lastPadding = DEFAULT_PADDING;
+  private _lastCornerRadius = DEFAULT_CORNER_RADIUS;
+
+  // Background redraw cache: skip Graphics.clear()+redraw when shape is unchanged
+  private _bgCacheKey = '';
+
   /** After layout, the computed card height. Parent should sync to data.h. */
   get computedHeight(): number {
     return this._cardH;
@@ -55,57 +73,122 @@ export class StickySprite extends Container {
     this.addChild(this._bg);
 
     // Text style
+    const fontSize = data.fontSize || 14;
     this._style = new TextStyle({
-      fontSize: data.fontSize || 14,
+      fontSize,
       fontFamily: data.fontFamily || 'Inter, system-ui, sans-serif',
       fill: data.textColor || '#1a1a1a',
       wordWrap: true,
       wordWrapWidth: Math.max(data.w - this._padding * 2, 1),
-      lineHeight: (data.fontSize || 14) * DEFAULT_LINE_HEIGHT,
+      lineHeight: fontSize * DEFAULT_LINE_HEIGHT,
     });
 
     this._text = new Text({ text: data.text || '', style: this._style });
     this._text.position.set(this._padding, this._padding);
     this.addChild(this._text);
 
+    // Snapshot initial state
+    this._lastText = data.text || '';
+    this._lastFontSize = fontSize;
+    this._lastFontFamily = data.fontFamily || 'Inter, system-ui, sans-serif';
+    this._lastTextColor = data.textColor || '#1a1a1a';
+    this._lastFill = this._bgColor;
+    this._lastW = data.w;
+    this._lastPadding = this._padding;
+    this._lastCornerRadius = this._cornerRadius;
+
     this._layout();
   }
 
   /**
    * Update from StickyObject data. Called by SceneManager._updateItem().
+   * Skips text/style/layout work when nothing actually changed.
    */
   updateFromData(data: StickyObject): void {
-    this._padding = data.padding ?? DEFAULT_PADDING;
-    this._cornerRadius = data.cornerRadius ?? DEFAULT_CORNER_RADIUS;
-    this._bgColor = data.fill || '#ffd43b';
-    this._cardW = data.w;
+    const padding = data.padding ?? DEFAULT_PADDING;
+    const cornerRadius = data.cornerRadius ?? DEFAULT_CORNER_RADIUS;
+    const bgColor = data.fill || '#ffd43b';
+    const w = data.w;
+    const text = data.text || '';
+    const fontSize = data.fontSize || 14;
+    const fontFamily = data.fontFamily || 'Inter, system-ui, sans-serif';
+    const textColor = data.textColor || '#1a1a1a';
 
-    // Update text content and style
-    this._text.text = data.text || '';
-    this._style.fontSize = data.fontSize || 14;
-    this._style.fontFamily = data.fontFamily || 'Inter, system-ui, sans-serif';
-    this._style.fill = data.textColor || '#1a1a1a';
-    this._style.wordWrapWidth = Math.max(data.w - this._padding * 2, 1);
-    this._style.lineHeight = (data.fontSize || 14) * DEFAULT_LINE_HEIGHT;
-    this._text.style = this._style;
+    // Check if anything actually changed
+    const textChanged = text !== this._lastText;
+    const styleChanged =
+      fontSize !== this._lastFontSize ||
+      fontFamily !== this._lastFontFamily ||
+      textColor !== this._lastTextColor;
+    const layoutChanged =
+      w !== this._lastW ||
+      padding !== this._lastPadding;
+    const bgChanged =
+      bgColor !== this._lastFill ||
+      cornerRadius !== this._lastCornerRadius;
 
-    this._text.position.set(this._padding, this._padding);
-    this._layout();
+    // Nothing changed — skip all work
+    if (!textChanged && !styleChanged && !layoutChanged && !bgChanged) return;
+
+    // Update cached state
+    this._padding = padding;
+    this._cornerRadius = cornerRadius;
+    this._bgColor = bgColor;
+    this._cardW = w;
+    this._lastText = text;
+    this._lastFontSize = fontSize;
+    this._lastFontFamily = fontFamily;
+    this._lastTextColor = textColor;
+    this._lastFill = bgColor;
+    this._lastW = w;
+    this._lastPadding = padding;
+    this._lastCornerRadius = cornerRadius;
+
+    // Only update text if content changed
+    if (textChanged) {
+      this._text.text = text;
+    }
+
+    // Only update style if style/layout props changed
+    if (styleChanged || layoutChanged) {
+      this._style.fontSize = fontSize;
+      this._style.fontFamily = fontFamily;
+      this._style.fill = textColor;
+      this._style.wordWrapWidth = Math.max(w - padding * 2, 1);
+      this._style.lineHeight = fontSize * DEFAULT_LINE_HEIGHT;
+      this._text.style = this._style;
+      this._text.position.set(padding, padding);
+    }
+
+    // Relayout if text, style, or dimensions changed (need remeasure)
+    if (textChanged || styleChanged || layoutChanged) {
+      this._layout();
+    } else if (bgChanged) {
+      // Only bg color/radius changed — redraw background without remeasuring text
+      this._drawBg();
+    }
   }
 
   /**
    * Recompute layout: measure text height, resize card, redraw background.
-   * Returns the new card height so the caller can sync data.h.
    */
   private _layout(): void {
-    // Measure the PixiJS text after style update
     const textBounds = this._text.getLocalBounds();
     const textH = textBounds.height;
 
-    // Card height: text + top/bottom padding, minimum height
     this._cardH = Math.max(textH + this._padding * 2, MIN_HEIGHT);
+    this._drawBg();
+  }
+
+  /**
+   * Redraw the rounded-rect background. Skips if shape is unchanged
+   * (same dimensions, color, radius).
+   */
+  private _drawBg(): void {
+    const cacheKey = `${this._cardW}|${this._cardH}|${this._bgColor}|${this._cornerRadius}`;
+    if (cacheKey === this._bgCacheKey) return;
+    this._bgCacheKey = cacheKey;
 
-    // Redraw background
     this._bg.clear();
     const color = parseInt(this._bgColor.replace('#', ''), 16) || 0xffd43b;
     this._bg.roundRect(0, 0, this._cardW, this._cardH, this._cornerRadius);