tauri-app: 8b click-through notifications

OS notification body already arrived as a 'maarcadetweet:notification'
DOM event (Phase 7b). The toast pill that surfaces the body is now
clickable: left-click navigates to the URL the notification was
about (at://<did>/<col>/<rkey> opens the thread, unknown URL
falls back to the home view); right-click dismisses without
navigating. tauri-plugin-notification v2.x does not expose a
reliable OS-level notification-click callback (it only shows the
notification), so the two-step pattern (OS click focuses the app
+ in-app toast click navigates) is the standard workaround.

lastNotificationUrl is now $state so the toast title updates
when a new notification arrives.

crates/tauri-app/src/App.svelte

@@ -96,9 +96,42 @@
   function onNotification(e: Event) {
     const detail = (e as CustomEvent<{ title: string; body: string; url: string | null }>).detail;
     if (detail) {
-      // Surface in the existing toast stack — works for both the
-      // OS-notification click and the in-app events.
-      pushToast("info", `notif: ${detail.title} — ${detail.body}`);
+      // Surface in the existing toast stack. The toast pill is
+      // clickable — clicking it navigates to the URL the notification
+      // was about (e.g. an at:// post URI). For OS-level
+      // notifications, the user has to first click the OS notification
+      // (which focuses the app) and then click the toast in the app
+      // to actually navigate; this is the limitation of the
+      // tauri-plugin-notification v2.x click callbacks.
+      pushToast(
+        "info",
+        `notif: ${detail.title} — ${detail.body}` + (detail.url ? "  (click to open)" : ""),
+      );
+      // Save the URL on a per-toast basis via a side-channel so the
+      // toast pill can navigate when clicked. We attach it to the
+      // notification event for simplicity (re-look-up via last).
+      lastNotificationUrl = detail.url ?? null;
+    }
+  }
+
+  let lastNotificationUrl: string | null = $state(null);
+
+  function openLastNotification() {
+    const url = lastNotificationUrl;
+    if (!url) return;
+    if (url.startsWith("at://")) {
+      // at://<did>/app.twi.post/<rkey> or at://<did>/app.bsky.feed.post/<rkey>
+      const parts = url.replace(/^at:\/\//, "").split("/");
+      const rkey = parts[parts.length - 1];
+      const did = parts[0];
+      if (rkey && did) {
+        // Use the existing thread-context machinery to open the post.
+        void openThread(`${did}/app.twi.post/${rkey}`);
+        lastNotificationUrl = null;
+      }
+    } else {
+      // unknown scheme — just open home
+      view = "home";
     }
   }
 
@@ -454,8 +487,22 @@
           class="toast-pill"
           class:toast-pill--err={t.kind === "error"}
           type="button"
-          onclick={() => (toasts = toasts.filter((x) => x.id !== t.id))}
-          title="dismiss"
+          onclick={() => {
+            // If this toast was a notification with a URL, navigate
+            // to it before dismissing. Otherwise just dismiss.
+            if (lastNotificationUrl) {
+              openLastNotification();
+            }
+            toasts = toasts.filter((x) => x.id !== t.id);
+          }}
+          oncontextmenu={(e) => {
+            // Right-click dismisses without navigating — useful when
+            // the user clicks a notification toast by mistake.
+            e.preventDefault();
+            lastNotificationUrl = null;
+            toasts = toasts.filter((x) => x.id !== t.id);
+          }}
+          title={lastNotificationUrl ? "click to open · right-click to dismiss" : "dismiss"}
         >
           {t.kind === "error" ? "err" : "info"}: {t.text}
         </button>