Morph page updates instead of replacing them

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

game.py

@@ -6753,6 +6753,7 @@ ORDER_RECIPES, ORDER_RAW = _order_sources()
 # line here (new / balance / fix), and a new release a new entry on top.
 PATCH_NOTES = [
     {"date": "2026-10-28", "title": "Queue", "notes": [
+        ("fix", "The page no longer redraws itself when an action finishes or a poll lands: scroll, hovers and tooltips stay put."),
         ("fix", "Crafting cards: buttons stay on one row on phones and narrow cards."),
         ("new", "\"Out of:\" lists every missing reagent."),
         ("new", "Updated guild roster layout"),

static/app.js

@@ -680,14 +680,58 @@ function render() {
   animate();
 }
 
-// Only touch the DOM when the markup changed. Replacing an element mid-swipe
+// Only touch the DOM when the markup changed, and then only the nodes that did:
-// cancels the swipe on iOS, and polls arrive every few seconds.
+// swapping the whole page flickers, drops hovers and scroll, and replacing an
+// element mid-swipe cancels the swipe on iOS. Polls arrive every few seconds.
 function setHtml(el, html) {
   if (el.dataset.html === html) return;
-  const scroll = el.scrollTop;
+  const next = document.createElement("template");
-  el.innerHTML = html;
+  next.innerHTML = html;
+  morphChildren(el, next.content);
   el.dataset.html = html;
-  el.scrollTop = scroll;
+}
+
+// Patch `from`'s children into `to`'s, pairing them up by position.
+function morphChildren(from, to) {
+  let old = from.firstChild, fresh = to.firstChild;
+  while (fresh) {
+    const after = fresh.nextSibling;
+    if (!old) from.appendChild(fresh);
+    else if (old.nodeType === fresh.nodeType && old.nodeName === fresh.nodeName) {
+      morphNode(old, fresh);
+      old = old.nextSibling;
+    } else {
+      const gone = old;
+      old = old.nextSibling;
+      from.replaceChild(fresh, gone);
+    }
+    fresh = after;
+  }
+  while (old) {
+    const gone = old;
+    old = old.nextSibling;
+    gone.remove();
+  }
+}
+
+function morphNode(old, fresh) {
+  if (old.nodeType !== Node.ELEMENT_NODE) {
+    if (old.nodeValue !== fresh.nodeValue) old.nodeValue = fresh.nodeValue;
+    return;
+  }
+  // A fire's canvas sizes itself and holds its drawing: setting its size clears it.
+  if (old.nodeName === "CANVAS" && old.dataset.flame === fresh.dataset.flame) return;
+  for (const { name } of [...old.attributes]) if (!fresh.hasAttribute(name)) old.removeAttribute(name);
+  for (const { name, value } of fresh.attributes) if (old.getAttribute(name) !== value) old.setAttribute(name, value);
+  morphChildren(old, fresh);
+  // What's typed or picked lives in properties, not attributes. Kept fields keep theirs (see render).
+  if (old.dataset.keep === undefined) {
+    if (old.nodeName === "INPUT") {
+      old.checked = fresh.checked;
+      if (old.value !== fresh.value) old.value = fresh.value;
+    } else if (old.nodeName === "TEXTAREA" && old.value !== fresh.value) old.value = fresh.value;
+    else if (old.nodeName === "SELECT") old.value = fresh.value;
+  }
 }
 
 function setMenu(open) {