diff --git a/hero.js b/hero.js
index 6b79b4e..bf52fbf 100644
--- a/hero.js
+++ b/hero.js
@@ -44,6 +44,9 @@ const TAU_MS = 140;
 // browser scales the canvas up to the screen; at 1080p that is about
 // 0.7 of the screen's pixels, at 4K about a third.
 const MAX_PIXELS = 1.2e6;
+// How long to wait for the app to adopt the piece before drawing it
+// anyway (no wasm, a blocked script): longer than any hydration.
+const ATTACH_FALLBACK_MS = 4000;
 
 // /usr/share/gpupaper/shaders/light_line.frag, as is.
 const LIGHT_LINE_FRAG = `// Lightning
@@ -232,6 +235,14 @@ const CSS = `
   height: 100%;
   display: block;
   pointer-events: none;
+  animation: westra-in 700ms ease-out;
+}
+
+/* They arrive after the app has hydrated (see attachWhenHydrated), so
+   they arrive as a fade rather than a pop. */
+@keyframes westra-in {
+  from { opacity: 0; }
+  to { opacity: 1; }
 }
 
 /* The name, laid out as the logo lays it out: a box with the logo's
@@ -245,6 +256,7 @@ const CSS = `
 .westra-name {
   position: absolute;
   inset: 0;
+  animation: westra-in 700ms ease-out;
   display: flex;
   align-items: center;
   justify-content: center;
@@ -308,7 +320,6 @@ const CSS = `
 `;
 
 function ensureStyle() {
-    if (DEBUG.has('nostyle')) return;
     if (document.getElementById(STYLE_ID)) return;
     const style = document.createElement('style');
     style.id = STYLE_ID;
@@ -337,7 +348,7 @@ class WestraHero {
         this.hero = container.closest('.hero') || container.parentElement;
         // Where the module's custom properties go: an element the app
         // never hydrates, so writing to it cannot disturb hydration.
-        this.host = DEBUG.has('nobody') ? document.createElement('div') : document.body;
+        this.host = document.body;
         this.reduced = window.matchMedia('(prefers-reduced-motion: reduce)');
         this.dark = window.matchMedia('(prefers-color-scheme: dark)');
 
@@ -356,9 +367,9 @@ class WestraHero {
         mark.append(a, b);
         this.name.append(mark);
         this.mark = mark;
-        // Both inside the piece, and nothing outside it (see .westra-line).
+        // Both go inside the piece, and nothing outside it (see
+        // .westra-line) - but not yet: see attachWhenHydrated().
         this.container = container;
-        if (!DEBUG.has('nodom')) container.append(this.canvas, this.name);
 
         this.width = 0;
         this.height = 1;
@@ -367,7 +378,44 @@ class WestraHero {
         this.t0 = performance.now();
         this.last = this.t0;
         this.raf = 0;
+        this.attached = false;
 
+        this.attachWhenHydrated();
+    }
+
+    // Portal starts this module at HTML parse time, before its app
+    // has hydrated the page, and hydration walks the DOM as served:
+    // nodes added to the piece before it runs throw it off (verified
+    // on the live site: with the DOM added at once the router never
+    // came up and every click was a full page load; with nothing
+    // added it hydrated every time). So the stylesheet goes in at
+    // once (the sticky header and the hidden wordmark are CSS) and
+    // the canvas and the name wait for the app to adopt this
+    // instance (portal sets __heroAdopted when it does), or for
+    // ATTACH_FALLBACK_MS if no app comes - then they fade in. On a
+    // client-side navigation back here the app mounts the module
+    // itself, after hydration, so they go in at once.
+    attachWhenHydrated() {
+        const ready = () => window.__heroAdopted === true || performance.now() - this.t0 > ATTACH_FALLBACK_MS;
+        const poll = () => {
+            if (this.stopped) return;
+            if (!ready()) {
+                this.raf = requestAnimationFrame(poll);
+                return;
+            }
+            // One more frame after the flag, so the app's own work
+            // for this frame is done before the piece changes.
+            this.raf = requestAnimationFrame(() => {
+                this.raf = 0;
+                if (!this.stopped) this.attach();
+            });
+        };
+        poll();
+    }
+
+    attach() {
+        this.attached = true;
+        this.container.append(this.canvas, this.name);
         this.gl = this.initGl();
         this.size();
 
@@ -583,6 +631,7 @@ class WestraHero {
     stop() {
         this.stopped = true;
         if (this.raf) cancelAnimationFrame(this.raf);
+        if (!this.attached) return;
         window.removeEventListener('resize', this._onResize);
         window.removeEventListener('scroll', this._onScroll);
         if (this.observer) this.observer.disconnect();
@@ -602,13 +651,6 @@ class WestraHero {
     }
 }
 
-// Temporary, to find what disturbs hydration on the live site:
-// ?hero=off mounts nothing, ?hero=nostyle skips the stylesheet,
-// ?hero=nobody skips the custom properties on <body>, ?hero=nodom
-// adds nothing to the piece. Removed once known.
-const DEBUG = new Set((new URLSearchParams(location.search).get('hero') || '').split(','));
-
 export function mount(container) {
-    if (DEBUG.has('off')) return { stop() {} };
     return new WestraHero(container);
 }