test(sync): audit browser recovery paths

examples/kanban/src/main.rs

@@ -842,6 +842,7 @@ async fn sync_acknowledgements(
         .get("reconnect")
         .filter(|value| !value.is_empty())
         .cloned();
+    let persistent_stream = reconnect_key.is_some();
 
     let mut sync = state.sync.lock().unwrap();
     if let Some(key) = reconnect_key {
@@ -921,22 +922,26 @@ async fn sync_acknowledgements(
     };
     drop(sync);
     let heartbeat_interval = state.acknowledgement_heartbeat_interval;
-    let heartbeat = stream::unfold(heartbeat_interval, |interval| async move {
-        tokio::time::sleep(interval).await;
-        Some((
-            Ok(Event::default()
-                .event("heartbeat")
-                .data("{\"status\":\"ok\"}")),
-            interval,
-        ))
-    });
-    Ok(
-        Sse::new(stream::iter(events).chain(heartbeat).boxed()).keep_alive(
-            KeepAlive::new()
-                .interval(heartbeat_interval)
-                .text("heartbeat"),
-        ),
-    )
+    let event_stream = stream::iter(events).boxed();
+    let response_stream = if persistent_stream {
+        let heartbeat = stream::unfold(heartbeat_interval, |interval| async move {
+            tokio::time::sleep(interval).await;
+            Some((
+                Ok(Event::default()
+                    .event("heartbeat")
+                    .data("{\"status\":\"ok\"}")),
+                interval,
+            ))
+        });
+        event_stream.chain(heartbeat).boxed()
+    } else {
+        event_stream
+    };
+    Ok(Sse::new(response_stream).keep_alive(
+        KeepAlive::new()
+            .interval(heartbeat_interval)
+            .text("heartbeat"),
+    ))
 }
 
 fn registry(state: Arc<AppState>) -> impl DispatchRegistry {

examples/kanban/static/sync.js

@@ -443,6 +443,21 @@ async function continuePendingWork() {
   setTimeout(() => synchronize(validatePending(commands[0])).catch(failPermanently), 0);
 }
 
+async function renewOfflineLease(command) {
+  if (stopped || root.getAttribute("data-sync-phase") !== "offline") return;
+  const lease = await claimUploaderLease(database);
+  publishLease(lease);
+  if (!lease.leader) {
+    setPhase("standby", "Another tab owns sync; waiting for lease takeover.");
+    leaseTimer = setTimeout(() => runLeaseLoop(command).catch(failPermanently), LEASE_POLL_MS);
+    return;
+  }
+  leaseTimer = setTimeout(
+    () => renewOfflineLease(command).catch(failPermanently),
+    LEASE_MS / 2,
+  );
+}
+
 async function synchronize(command) {
   if (synchronizing) return;
   synchronizing = true;
@@ -455,7 +470,10 @@ async function synchronize(command) {
   }
   clearTimeout(leaseTimer);
   leaseTimer = setTimeout(() => {
-    if (!stopped && root.getAttribute("data-sync-phase") !== "acknowledged") {
+    if (stopped || root.getAttribute("data-sync-phase") === "acknowledged") return;
+    if (root.getAttribute("data-sync-phase") === "offline") {
+      renewOfflineLease(command).catch(failPermanently);
+    } else {
       synchronize(command).catch(failPermanently);
     }
   }, LEASE_MS / 2);

examples/kanban/tests/browser_e2e.rs

@@ -829,12 +829,16 @@ async fn schema_upgrade_preserves_queued_order_and_local_intent() -> WebDriverRe
             ])
         );
 
-        driver.find(By::Css("[data-sync-retry]")).await?.click().await?;
-        wait_until(
-            &driver,
-            "const root = document.querySelector('[data-kanban-sync]'); return root?.getAttribute('data-sync-phase') === 'backpressured' && root?.getAttribute('data-sync-pending-count') === '1'",
-        )
-        .await?;
+        for expected_pending in [2, 1] {
+            driver.find(By::Css("[data-sync-retry]")).await?.click().await?;
+            wait_until(
+                &driver,
+                &format!(
+                    "const root = document.querySelector('[data-kanban-sync]'); return root?.getAttribute('data-sync-phase') === 'offline' && root?.getAttribute('data-sync-pending-count') === '{expected_pending}'"
+                ),
+            )
+            .await?;
+        }
         driver.find(By::Css("[data-sync-retry]")).await?.click().await?;
         wait_until(
             &driver,