desktop: reminders reach you when the window isn't in front

A Rust worker reads due reminders from the local store every 15 s and
announces each occurrence once: always to the main window as a toast, and
as a system notification (tauri-plugin-notification) when that window
isn't focused. The page no longer polls on the desktop; its Notification
went nowhere in WebKitGTK and its timer stopped with the window. The
Reminders page says what each surface actually does.

Core gains store::due_reminders, compared by instant, not by string.

Refs #5171

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/stores/reminders.ts

@@ -1,23 +1,33 @@
 import { defineStore } from "pinia";
 import { ref } from "vue";
 import { repo } from "../adapters";
+import { isDesktop, onReminderDue } from "../desktop/bridge";
 import router from "../router";
 import { useUiStore } from "./ui";
 import type { Note } from "./notes";
 
-// Foreground reminder delivery — NO Web Push / service worker (per operator). While
-// the app is open, poll for due reminders and surface each once as a toast (and, if
-// the user opted in, a page-context OS notification). Real background delivery is a
-// native-client concern.
+// Reminder delivery. In a browser it is foreground only — NO Web Push / service
+// worker (per operator): while the tab is open, poll for due reminders and surface
+// each once as a toast (and, if the user opted in, a page-context OS notification).
+//
+// The desktop doesn't poll here. Its Rust worker reads the local store, decides
+// what is due, raises the system notification itself when the window isn't in
+// front, and tells this page so it can show the toast (#5171). The page's
+// `Notification` went nowhere in WebKitGTK, and its timer stopped with the window.
 const POLL_MS = 45_000;
 const RECENT_MS = 15 * 60 * 1000; // on first load, only announce reminders due this recently
 
 export const useReminderStore = defineStore("reminders", () => {
-  const osSupported = typeof Notification !== "undefined";
+  const desktop = isDesktop();
+  // The desktop raises its own system notifications; there is nothing to opt into.
+  const osSupported = !desktop && typeof Notification !== "undefined";
   const osEnabled = ref(osSupported && Notification.permission === "granted");
   // note id → the remind_at we already fired, so each occurrence notifies at most once.
   const notified = new Map<string, string>();
   let timer: ReturnType<typeof setInterval> | undefined;
+  // The desktop's subscription to its reminder worker, held as the promise so stop()
+  // can undo one whose registration hasn't finished yet.
+  let listening: Promise<() => void> | undefined;
   let primed = false;
 
   // Single owner of the reminders endpoint — the RemindersView reads its list through
@@ -26,8 +36,17 @@ export const useReminderStore = defineStore("reminders", () => {
     return repo.notes.reminders();
   }
 
+  /** Show the in-app toast for a due reminder; returns the title it showed. */
+  function toast(id: string, displayTitle: string): string {
+    const title = displayTitle || "Reminder";
+    useUiStore().showToast(`⏰ ${title}`, {
+      label: "Open",
+      run: () => void router.push({ path: "/", query: { open: id } }),
+    });
+    return title;
+  }
+
   async function check(): Promise<void> {
-    const ui = useUiStore();
     let notes: Note[];
     try {
       notes = await fetchReminders();
@@ -42,11 +61,7 @@ export const useReminderStore = defineStore("reminders", () => {
       notified.set(n.id, n.remind_at);
       // Silently prime a stale backlog on first load; only announce recently-due ones.
       if (!primed && now - due > RECENT_MS) continue;
-      const title = n.display_title || "Reminder";
-      ui.showToast(`⏰ ${title}`, {
-        label: "Open",
-        run: () => void router.push({ path: "/", query: { open: n.id } }),
-      });
+      const title = toast(n.id, n.display_title);
       if (osEnabled.value) {
         try {
           new Notification("Inkwell reminder", { body: title });
@@ -59,6 +74,10 @@ export const useReminderStore = defineStore("reminders", () => {
   }
 
   function start(): void {
+    if (desktop) {
+      if (!listening) listening = onReminderDue((r) => void toast(r.id, r.title));
+      return;
+    }
     if (timer) return;
     void check();
     timer = setInterval(() => void check(), POLL_MS);
@@ -66,6 +85,8 @@ export const useReminderStore = defineStore("reminders", () => {
   function stop(): void {
     if (timer) clearInterval(timer);
     timer = undefined;
+    void listening?.then((off) => off());
+    listening = undefined;
   }
   async function enableOs(): Promise<void> {
     if (!osSupported) return;