diff --git a/hero.js b/hero.js
index 13ecc74..3393b6c 100644
--- a/hero.js
+++ b/hero.js
@@ -149,8 +149,13 @@ const CSS = `
   /* Sticky at the viewport top for the whole scroll (its containing
      block is the page itself), z-index 0 so the cards (z-index 1)
      stack over it. The height is a floor, frozen to a measured pixel
-     value by the module once it runs (see size()); the svh ladder is
-     the first paint and the no-JS fallback. A floor and not a height,
+     value by the module once it runs (see size()) - as a custom
+     property on <body>, never as an inline style on the header: the
+     module runs before the app hydrates, and an attribute written
+     onto an element the app is about to hydrate throws the hydration
+     off, and with it client-side navigation (uhhm's hero shows the
+     same). The svh ladder is the first paint and the no-JS fallback.
+     A floor and not a height,
      so a copy that needs more than a screen (a phone) grows the header
      rather than being clipped, and the cards start under it. */
   position: sticky;
@@ -160,6 +165,7 @@ const CSS = `
   width: 100%;
   min-height: 100vh;
   min-height: 100svh;
+  min-height: var(--westra-hero-h, 100svh);
   padding: 0;
   justify-content: flex-end;
   overflow: hidden;
@@ -200,8 +206,11 @@ const CSS = `
   transform: none;
 }
 
+/* The copy's fade is a custom property too, for the same reason. */
 .hero-module .hero-copy {
   position: static;
+  opacity: var(--westra-copy, 1);
+  visibility: var(--westra-copy-vis, visible);
   padding: 0 1.5rem 3.5rem;
   gap: 0.6rem;
   text-shadow: 0 0.12em 1.4em var(--hero-glow);
@@ -325,7 +334,9 @@ class WestraHero {
         ensureStyle();
         this.stopped = false;
         this.hero = container.closest('.hero') || container.parentElement;
-        this.copy = this.hero ? this.hero.querySelector('.hero-copy') : null;
+        // Where the module's custom properties go: an element the app
+        // never hydrates, so writing to it cannot disturb hydration.
+        this.host = document.body;
         this.reduced = window.matchMedia('(prefers-reduced-motion: reduce)');
         this.dark = window.matchMedia('(prefers-color-scheme: dark)');
 
@@ -418,12 +429,11 @@ class WestraHero {
         const p = ease(this.progress);
         this.name.style.setProperty('--p', p.toFixed(4));
         // The copy goes sooner than the name: it has to be gone before
-        // the first card reaches it, on a short screen too.
-        if (this.copy) {
-            const visible = 1 - clamp01(this.progress * 2.5);
-            this.copy.style.opacity = visible.toFixed(3);
-            this.copy.style.visibility = visible <= 0.01 ? 'hidden' : '';
-        }
+        // the first card reaches it, on a short screen too. Written
+        // on <body>, which the app does not hydrate (see the CSS).
+        const visible = 1 - clamp01(this.progress * 2.5);
+        this.host.style.setProperty('--westra-copy', visible.toFixed(3));
+        this.host.style.setProperty('--westra-copy-vis', visible <= 0.01 ? 'hidden' : 'visible');
 
         this.draw(this.reduced.matches ? 0 : (now - this.t0) / 1000);
 
@@ -446,7 +456,7 @@ class WestraHero {
     size() {
         this.width = window.innerWidth;
         this.height = Math.max(1, window.innerHeight);
-        if (this.hero) this.hero.style.minHeight = this.height + 'px';
+        this.host.style.setProperty('--westra-hero-h', this.height + 'px');
         this.fit();
     }
 
@@ -583,10 +593,8 @@ class WestraHero {
             const lose = this.gl.getExtension('WEBGL_lose_context');
             if (lose) lose.loseContext();
         }
-        if (this.hero) this.hero.style.minHeight = '';
-        if (this.copy) {
-            this.copy.style.opacity = '';
-            this.copy.style.visibility = '';
+        for (const prop of ['--westra-hero-h', '--westra-copy', '--westra-copy-vis']) {
+            this.host.style.removeProperty(prop);
         }
         this.canvas.remove();
         this.name.remove();