take aspect ratio into account when rasterizing

CSS custom property changes (--pxicon-ap-size, --pxicon-mode) aren't
observed by MutationObserver/ResizeObserver, so a live-mounted <px-icon>
never rechecked its config. Add a pxicon:refresh document event + exported
refreshAll() helper; demo calls it from its control handlers.

examples/index.html

@@ -170,7 +170,7 @@
 </div>
 
 <script type="module">
-import '../px-icon.js';
+import { refreshAll } from '../px-icon.js';
 
 const apSizeInput = document.getElementById('apSize');
 const apSizeVal = document.getElementById('apSizeVal');
@@ -181,6 +181,7 @@ function applyConfig() {
   apSizeVal.textContent = ap;
   document.documentElement.style.setProperty('--pxicon-ap-size', ap + 'px');
   document.documentElement.style.setProperty('--pxicon-mode', modeSelect.value);
+  refreshAll();
 }
 apSizeInput.addEventListener('input', applyConfig);
 modeSelect.addEventListener('change', applyConfig);

px-icon.js

@@ -15,6 +15,14 @@ const DEFAULT_AP_SIZE = 8;
 const DEFAULT_MODE = 'average';
 const SUPERSAMPLE = 8; // per grid cell, for point-sample mode
 
+// CSS custom properties (--pxicon-ap-size, --pxicon-mode, ...) aren't
+// observable the way DOM mutations/resizes are: MutationObserver and
+// ResizeObserver don't fire when a cascaded custom property changes.
+// Instances listen for this document-level event so config changes (e.g.
+// a page-level theme/control update) can trigger a re-check without every
+// caller needing to touch each <px-icon>'s internals.
+const REFRESH_EVENT = 'pxicon:refresh';
+
 // key -> Promise<HTMLCanvasElement> (the small pre-upscale grid raster)
 const rasterCache = new Map();
 
@@ -131,12 +139,15 @@ class PxIcon extends HTMLElement {
     // e.g. a morph swapping in a different icon.
     this._observer ??= new MutationObserver(() => this._scheduleRender());
     this._observer.observe(this, { childList: true, subtree: true, attributes: true, characterData: true });
+    this._refreshHandler ??= () => this._scheduleRender();
+    document.addEventListener(REFRESH_EVENT, this._refreshHandler);
     this._scheduleRender();
   }
 
   disconnectedCallback() {
     this._observer?.disconnect();
     this._resizeObserver?.disconnect();
+    document.removeEventListener(REFRESH_EVENT, this._refreshHandler);
   }
 
   _upgrade() {
@@ -181,10 +192,12 @@ class PxIcon extends HTMLElement {
     const apSize = parseFloat(cs.getPropertyValue('--pxicon-ap-size')) || DEFAULT_AP_SIZE;
     const mode = (cs.getPropertyValue('--pxicon-mode') || DEFAULT_MODE).trim();
 
-    const displaySize = Math.max(this.clientWidth, this.clientHeight) || 24;
-    const snapped = snapToGrid(displaySize, apSize);
-    const gridW = Math.max(1, Math.round(snapped / apSize));
-    const gridH = gridW;
+    const displayW = this.clientWidth || 24;
+    const displayH = this.clientHeight || 24;
+    const snappedW = snapToGrid(displayW, apSize);
+    const snappedH = snapToGrid(displayH, apSize);
+    const gridW = Math.max(1, Math.round(snappedW / apSize));
+    const gridH = Math.max(1, Math.round(snappedH / apSize));
 
     const svgMarkup = svgEl.outerHTML;
     const key = `${svgMarkup}|${mode}|${gridW}x${gridH}`;
@@ -200,13 +213,14 @@ class PxIcon extends HTMLElement {
     const gridCanvas = await getGridRaster(svgMarkup, mode, gridW, gridH);
 
     const dpr = window.devicePixelRatio || 1;
-    const backingSize = Math.round(snapped * dpr);
-    this._canvas.width = backingSize;
-    this._canvas.height = backingSize;
+    const backingW = Math.round(snappedW * dpr);
+    const backingH = Math.round(snappedH * dpr);
+    this._canvas.width = backingW;
+    this._canvas.height = backingH;
     const ctx = this._canvas.getContext('2d');
     ctx.imageSmoothingEnabled = false;
-    ctx.clearRect(0, 0, backingSize, backingSize);
-    ctx.drawImage(gridCanvas, 0, 0, backingSize, backingSize);
+    ctx.clearRect(0, 0, backingW, backingH);
+    ctx.drawImage(gridCanvas, 0, 0, backingW, backingH);
 
     if (this._slot.isConnected) {
       // first successful raster: swap the placeholder slot for the
@@ -219,4 +233,12 @@ class PxIcon extends HTMLElement {
 
 customElements.define('px-icon', PxIcon);
 
-export { PxIcon, rasterCache };
+// Call after changing a --pxicon-* custom property (e.g. on :root, or any
+// ancestor of a group of icons) to make every connected <px-icon> re-check
+// its computed config and re-render if it actually changed. Cheap to call
+// broadly: each instance's own key check skips the work if nothing did.
+function refreshAll() {
+  document.dispatchEvent(new CustomEvent(REFRESH_EVENT));
+}
+
+export { PxIcon, rasterCache, refreshAll };