feat(favicon): swap tab favicon for SFW vs NSFW boards

src/hooks/use-theme.ts

@@ -7,6 +7,7 @@ import { useResolvedSubplebbitAddress } from './use-resolved-subplebbit-address'
 import { useAccountComment } from '@bitsocialhq/pkc-react-hooks';
 import useSpecialThemeStore from '../stores/use-special-theme-store';
 import { isChristmas } from '../lib/utils/time-utils';
+import { updateFavicon, isSfwBoard } from '../lib/update-favicon';
 
 const themeClasses = ['yotsuba', 'yotsuba-b', 'futaba', 'burichan', 'tomorrow', 'photon'];
 
@@ -80,11 +81,26 @@ const useTheme = (): [string, (theme: string) => void] => {
     return storedTheme || 'yotsuba';
   }, [location.pathname, isEnabled, isInAllView, isInSubscriptionsView, isInModView, subplebbitAddress, directories, themes]);
 
+  const sfw = isSfwBoard({
+    pathname: location.pathname,
+    isSpecialTheme: !!isEnabled,
+    isInAllView,
+    isInSubscriptionsView,
+    isInModView,
+    subplebbitAddress,
+    directories,
+  });
+
   // Update DOM class when theme changes
   useEffect(() => {
     updateThemeClass(currentTheme);
   }, [currentTheme]);
 
+  // Update favicon when SFW status changes (separate effect for independent lifecycle)
+  useEffect(() => {
+    updateFavicon(sfw);
+  }, [sfw]);
+
   const setSubplebbitTheme = useCallback(
     async (newTheme: string) => {
       if (isInAllView || isInSubscriptionsView || isInModView) {

src/lib/update-favicon.ts

@@ -0,0 +1,54 @@
+const DEFAULT_FAVICON = '/favicon.ico';
+const SFW_FAVICON = '/favicon2.ico';
+
+let currentHref: string | null = null;
+
+/**
+ * Swap the tab favicon between the default (NSFW/home) and SFW variants.
+ * Uses remove-and-recreate to bypass aggressive browser favicon caching.
+ */
+export const updateFavicon = (isSfw: boolean): void => {
+  const href = isSfw ? SFW_FAVICON : DEFAULT_FAVICON;
+  if (href === currentHref) return;
+  currentHref = href;
+
+  const existing = document.querySelector<HTMLLinkElement>('link[rel="icon"]');
+  if (existing) existing.remove();
+
+  const link = document.createElement('link');
+  link.rel = 'icon';
+  link.href = href;
+  document.head.appendChild(link);
+};
+
+/**
+ * Determine whether the current navigation context is a SFW board.
+ *
+ * Pure function — no hooks, no side-effects, fully testable.
+ */
+export const isSfwBoard = ({
+  pathname,
+  isSpecialTheme,
+  isInAllView,
+  isInSubscriptionsView,
+  isInModView,
+  subplebbitAddress,
+  directories,
+}: {
+  pathname: string;
+  isSpecialTheme: boolean;
+  isInAllView: boolean;
+  isInSubscriptionsView: boolean;
+  isInModView: boolean;
+  subplebbitAddress: string | undefined;
+  directories: { address: string; nsfw?: boolean }[];
+}): boolean => {
+  if (pathname === '/' || pathname.startsWith('/rules')) return false;
+  if (isSpecialTheme) return false;
+  if (isInAllView || isInSubscriptionsView || isInModView) return false;
+
+  if (!subplebbitAddress) return false;
+
+  const entry = directories.find((d) => d.address === subplebbitAddress);
+  return !entry?.nsfw;
+};