Enhance map update handling and connection stability

- Introduced mechanisms to detect stale connections in the map updates, allowing for automatic reconnection if no messages are received within a specified timeframe.
- Updated the `refresh` method in `SmartTileLayer` to return a boolean indicating whether the tile was refreshed, improving the handling of tile updates.
- Enhanced the `Send` method in the `Topic` struct to drop messages for full subscribers while keeping them subscribed, ensuring continuous delivery of future updates.
- Added a keepalive mechanism in the `WatchGridUpdates` handler to maintain the connection and prevent timeouts.

frontend-nuxt/composables/useMapUpdates.ts

@@ -38,6 +38,9 @@ export interface UseMapUpdatesReturn {
 
 const RECONNECT_INITIAL_MS = 1000
 const RECONNECT_MAX_MS = 30000
+/** If no SSE message received for this long, treat connection as stale and reconnect. */
+const STALE_CONNECTION_MS = 65000
+const STALE_CHECK_INTERVAL_MS = 30000
 
 export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesReturn {
   const { backendBase, layer, overlayLayer, map, getCurrentMapId, onMerge, connectionStateRef } = options
@@ -50,6 +53,8 @@ export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesRet
   let batchScheduled = false
   let source: EventSource | null = null
   let reconnectTimeoutId: ReturnType<typeof setTimeout> | null = null
+  let staleCheckIntervalId: ReturnType<typeof setInterval> | null = null
+  let lastMessageTime = 0
   let reconnectDelayMs = RECONNECT_INITIAL_MS
   let destroyed = false
 
@@ -79,15 +84,22 @@ export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesRet
       overlayLayer.cache[key] = u.T
     }
     const visible = getVisibleTileBounds()
+    // u.Z is backend storage zoom (0..5); visible.zoom is map zoom (1..6). With zoomReverse, current backend Z = maxZoom - mapZoom.
+    const currentBackendZ = visible ? layer.options.maxZoom - visible.zoom : null
+    let needRedraw = false
     for (const u of updates) {
-      if (visible && u.Z !== visible.zoom) continue
+      if (visible && currentBackendZ != null && u.Z !== currentBackendZ) continue
       if (
         visible &&
         (u.X < visible.minX || u.X > visible.maxX || u.Y < visible.minY || u.Y > visible.maxY)
       )
         continue
-      if (layer.map === u.M) layer.refresh(u.X, u.Y, u.Z)
-      if (overlayLayer.map === u.M) overlayLayer.refresh(u.X, u.Y, u.Z)
+      if (layer.map === u.M && !layer.refresh(u.X, u.Y, u.Z)) needRedraw = true
+      if (overlayLayer.map === u.M && !overlayLayer.refresh(u.X, u.Y, u.Z)) needRedraw = true
+    }
+    if (needRedraw) {
+      layer.redraw()
+      overlayLayer.redraw()
     }
   }
 
@@ -99,12 +111,30 @@ export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesRet
 
   function connect() {
     if (destroyed || !import.meta.client) return
+    if (staleCheckIntervalId != null) {
+      clearInterval(staleCheckIntervalId)
+      staleCheckIntervalId = null
+    }
     source = new EventSource(updatesUrl)
     if (connectionStateRef) connectionStateRef.value = 'connecting'
 
     source.onopen = () => {
       if (connectionStateRef) connectionStateRef.value = 'open'
+      lastMessageTime = Date.now()
       reconnectDelayMs = RECONNECT_INITIAL_MS
+      staleCheckIntervalId = setInterval(() => {
+        if (destroyed || !source) return
+        if (Date.now() - lastMessageTime > STALE_CONNECTION_MS) {
+          if (staleCheckIntervalId != null) {
+            clearInterval(staleCheckIntervalId)
+            staleCheckIntervalId = null
+          }
+          source.close()
+          source = null
+          if (connectionStateRef) connectionStateRef.value = 'error'
+          connect()
+        }
+      }, STALE_CHECK_INTERVAL_MS)
     }
 
     source.onerror = () => {
@@ -121,6 +151,7 @@ export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesRet
     }
 
     source.onmessage = (event: MessageEvent) => {
+      lastMessageTime = Date.now()
       if (connectionStateRef) connectionStateRef.value = 'open'
       try {
         const raw: unknown = event?.data
@@ -157,6 +188,10 @@ export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesRet
 
   function cleanup() {
     destroyed = true
+    if (staleCheckIntervalId != null) {
+      clearInterval(staleCheckIntervalId)
+      staleCheckIntervalId = null
+    }
     if (reconnectTimeoutId != null) {
       clearTimeout(reconnectTimeoutId)
       reconnectTimeoutId = null