fix: favicon badge — remove favicon.ico, fix Firefox compat

- Delete app/favicon.ico so Next.js renders a single <link rel="icon">
  for icon.svg. With two icon links in the DOM, browsers disagreed on
  which to use: Chrome and Firefox on Linux both picked the *first* one,
  making the dynamically-appended badge link invisible.
- Mutate href on the existing <link> instead of injecting a second one.
  Firefox only updates the tab icon when the href of the element it
  already tracks changes — adding new <link> nodes dynamically is ignored.
- Simplify image loading: replace fetch → blob → FileReader → Image
  chain with new Image() + crossOrigin="anonymous".
- Fix badge border in Safari 15 fallback: use strokeRect instead of
  stroke() after fillRect (fillRect does not add to the canvas path).

hooks/use-favicon-badge.ts

@@ -3,81 +3,81 @@
 import { useEffect, useRef } from "react";
 
 const SIZE = 32;
-const DYNAMIC_ATTR = "data-dynamic-favicon";
 
 export function useFaviconBadge(count: number) {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
   const imageRef = useRef<HTMLImageElement | null>(null);
+  const baseLinkRef = useRef<HTMLLinkElement | null>(null);
+  const originalHrefRef = useRef<string>("");
+  const imageLoaded = useRef(false);
   const countRef = useRef(count);
   countRef.current = count;
 
   useEffect(() => {
-    // Grab the base favicon href from whatever the document currently has
-    // (Next.js renders one from app/icon.svg). We NEVER remove or edit
-    // that link — Next.js's metadata reconciler owns it and pulling it
-    // out from under React crashes reconciliation with
-    // "parentNode is null". Our badge lives on its own link tagged with
-    // data-dynamic-favicon.
-    const baseLink = document.querySelector<HTMLLinkElement>("link[rel~='icon']:not([data-dynamic-favicon])");
+    // We mutate href on the existing Next.js-rendered <link> directly.
+    // Firefox only updates the tab favicon when the href of the element it
+    // already tracks changes — it ignores new <link> nodes added dynamically.
+    // Changing href is safe: the React reconciler crash ("parentNode is null")
+    // only happens when a tracked node is *removed* from the DOM, not when
+    // its attributes change. On cleanup we restore the original href.
+    const baseLink = document.querySelector<HTMLLinkElement>("link[rel~='icon']");
     if (!baseLink?.href) return;
 
+    baseLinkRef.current = baseLink;
+    originalHrefRef.current = baseLink.href;
+
     const canvas = document.createElement("canvas");
     canvas.width = SIZE;
     canvas.height = SIZE;
     canvasRef.current = canvas;
 
-    fetch(baseLink.href)
-      .then((r) => r.blob())
-      .then((blob) => {
-        const reader = new FileReader();
-        reader.onloadend = () => {
-          const img = new Image();
-          img.onload = () => {
-            imageRef.current = img;
-            if (countRef.current > 0) {
-              applyBadge(canvas, img, countRef.current);
-            }
-          };
-          img.src = reader.result as string;
-        };
-        reader.readAsDataURL(blob);
-      })
-      .catch(() => {
-        /* favicon not loadable — badge will draw without base icon */
-      });
+    const img = new Image();
+    img.crossOrigin = "anonymous";
+    img.onload = () => {
+      imageLoaded.current = true;
+      imageRef.current = img;
+      if (countRef.current > 0) {
+        drawBadge(canvas, img, countRef.current, baseLink);
+      }
+    };
+    img.onerror = () => {
+      imageLoaded.current = true;
+    };
+    img.src = originalHrefRef.current;
 
     return () => {
-      clearDynamicFavicon();
+      if (baseLinkRef.current) {
+        baseLinkRef.current.href = originalHrefRef.current;
+      }
     };
   }, []);
 
   useEffect(() => {
+    const baseLink = baseLinkRef.current;
+    if (!baseLink || !imageLoaded.current) return;
+
     if (count <= 0) {
-      clearDynamicFavicon();
+      baseLink.href = originalHrefRef.current;
       return;
     }
 
     if (canvasRef.current) {
-      applyBadge(canvasRef.current, imageRef.current, count);
+      drawBadge(canvasRef.current, imageRef.current, count, baseLink);
     }
   }, [count]);
 }
 
-function applyBadge(
+function drawBadge(
   canvas: HTMLCanvasElement,
   image: HTMLImageElement | null,
   count: number,
+  link: HTMLLinkElement,
 ) {
   const ctx = canvas.getContext("2d");
-  if (!ctx) {
-    return;
-  }
+  if (!ctx) return;
 
   ctx.clearRect(0, 0, SIZE, SIZE);
-
-  if (image) {
-    ctx.drawImage(image, 0, 0, SIZE, SIZE);
-  }
+  if (image) ctx.drawImage(image, 0, 0, SIZE, SIZE);
 
   const label = count > 9 ? "+" : String(count);
   const fontSize = SIZE * 0.55;
@@ -92,46 +92,21 @@ function applyBadge(
   const y = SIZE - badgeH;
 
   ctx.fillStyle = "#ef4444";
-  ctx.beginPath();
-  // roundRect is Baseline 2023; fall back to fillRect on Safari 15 and below.
-  if (typeof ctx.roundRect === "function") {
-    ctx.roundRect(x, y, badgeW, badgeH, 3);
-    ctx.fill();
-  } else {
-    ctx.fillRect(x, y, badgeW, badgeH);
-  }
-
   ctx.strokeStyle = "#b91c1c";
   ctx.lineWidth = 1;
-  ctx.stroke();
+  // roundRect is Baseline 2023; fall back to fillRect on Safari 15 and below.
+  if (typeof ctx.roundRect === "function") {
+    ctx.beginPath();
+    ctx.roundRect(x, y, badgeW, badgeH, 3);
+    ctx.fill();
+    ctx.stroke();
+  } else {
+    ctx.fillRect(x, y, badgeW, badgeH);
+    ctx.strokeRect(x, y, badgeW, badgeH);
+  }
 
   ctx.fillStyle = "#ffffff";
   ctx.fillText(label, x + padding, y + padding / 2);
 
-  setDynamicFavicon(canvas.toDataURL("image/png"));
-}
-
-/**
- * Upsert a dynamic favicon link marked with data-dynamic-favicon. The
- * app/icon.svg managed by Next.js is left alone. Browsers pick the
- * last matching link for rel="icon", so the dynamic link takes
- * precedence on Chromium; Firefox/Safari fall back to the static icon,
- * which is fine — the count-based badge remains a Chromium nicety.
- */
-function setDynamicFavicon(href: string) {
-  let link = document.querySelector<HTMLLinkElement>(`link[${DYNAMIC_ATTR}]`);
-  if (!link) {
-    link = document.createElement("link");
-    link.setAttribute(DYNAMIC_ATTR, "");
-    link.rel = "icon";
-    link.type = "image/png";
-    document.head.appendChild(link);
-  }
-  if (link.href !== href) {
-    link.href = href;
-  }
-}
-
-function clearDynamicFavicon() {
-  document.querySelector(`link[${DYNAMIC_ATTR}]`)?.remove();
+  link.href = canvas.toDataURL("image/png");
 }