Version the brand images' URLs, so a new mark reaches returning visitors

The logo, favicons and app icons are served from public/img under fixed
names with a browser cache of hours, and the service worker fetches them
through that cache. After the mark changed on 2026-09-27, returning
visitors kept the old cat until their copies expired, and the favicon
and an installed app's icon hold on longer still.

Every URL that names one now carries ?v=BRAND_V (src/lib/brand.ts,
brandImage()): the header, sign-in, About, the mail empty state, the
notification icons, index.html's favicon links, the manifest's icons
and the service worker's shell and notification icons. Date-stamped,
never a counter, for the sites' ASSET_V reason; the three static files
carry the value written out, and the comment says to keep them in step.

web/src/lib/brand.ts

@@ -1,4 +1,5 @@
 import { useSession } from "@/store/session";
+import { withBase } from "@/lib/basePath";
 
 /**
  * What this instance calls itself, when nothing has said otherwise yet.
@@ -36,3 +37,25 @@ export function useAppName(): string {
 export function currentAppName(): string {
   return useSession.getState().session?.ihasmail?.appName?.trim() || DEFAULT_APP_NAME;
 }
+
+/**
+ * The brand images' version, carried as `?v=` on every URL that names one.
+ *
+ * The images live in `public/img` under fixed names and are served with a
+ * browser cache of hours, so replacing one (the mark changed on 2026-09-27)
+ * left returning visitors on the old picture until their copy expired -- and
+ * the favicon and an installed app's icon hold on longer still. A new value
+ * here is a new URL everywhere at once.
+ *
+ * Date-stamped with a letter for a second change the same day, never a
+ * counter, for the reason the sites give for ASSET_V: a value that could have
+ * been requested before may already be cached, with old bytes behind it.
+ * `index.html`, `public/manifest.webmanifest` and `public/sw.js` can't import
+ * this, so they carry the same value written out; keep the four in step.
+ */
+export const BRAND_V = "2026-09-27a";
+
+/** A brand image's URL under the mount, versioned: `brandImage("/img/logo.png")`. */
+export function brandImage(path: string): string {
+  return withBase(`${path}?v=${BRAND_V}`);
+}

web/src/lib/notify/notify.ts

@@ -1,4 +1,4 @@
-import { withBase } from "../basePath";
+import { brandImage } from "@/lib/brand";
 
 let baseTitle = "inbuxa";
 let faviconCanvas: HTMLCanvasElement | null = null;
@@ -40,13 +40,13 @@ export function setUnreadBadge(count: number): void {
     if (!link) return;
     if (!baseFavicon) {
       baseFavicon = new Image();
-      baseFavicon.src = withBase("/img/favicon-64.png");
+      baseFavicon.src = brandImage("/img/favicon-64.png");
       baseFavicon.onload = () => setUnreadBadge(count);
       return;
     }
     if (!baseFavicon.complete) return;
     if (count <= 0) {
-      link.href = withBase("/img/favicon-64.png");
+      link.href = brandImage("/img/favicon-64.png");
       return;
     }
     faviconCanvas ??= document.createElement("canvas");
@@ -95,7 +95,7 @@ export function showNotification(title: string, opts: NotificationOptions & { on
   if (!("Notification" in window) || Notification.permission !== "granted") return;
   if (document.visibilityState === "visible" && document.hasFocus()) return;
   const { onClick, ...options } = opts;
-  const full = { icon: withBase("/img/icon-192.png"), badge: withBase("/img/favicon-64.png"), ...options };
+  const full = { icon: brandImage("/img/icon-192.png"), badge: brandImage("/img/favicon-64.png"), ...options };
   const viaWorker = navigator.serviceWorker?.controller ? navigator.serviceWorker.ready : null;
   if (viaWorker) {
     void viaWorker.then((reg) => reg.showNotification(title, full)).catch(() => undefined);