fix: preserve context across SSE reconnects on tab visibility change

Datastar aborts SSE on visibilitychange (tab hidden) and reconnects
when visible. The previous cleanup-on-disconnect destroyed the context
before the client could reconnect. Now SSE disconnect does a soft
teardown (mark disconnected, keep context alive) and reconnect drains
stale patches before resuming. The reaper uses disconnect time instead
of creation time so recently-disconnected contexts aren't prematurely
reaped.

context.go

@@ -39,8 +39,9 @@ type Context struct {
 	subscriptions     []Subscription
 	subsMu            sync.Mutex
 	disposeOnce       sync.Once
-	createdAt         time.Time
-	sseConnected      atomic.Bool
+	createdAt           time.Time
+	sseConnected        atomic.Bool
+	sseDisconnectedAt   atomic.Pointer[time.Time]
 }
 
 // View defines the UI rendered by this context.

via.go

@@ -318,8 +318,19 @@ func (v *V) reapOrphanedContexts(ttl time.Duration) {
 	v.contextRegistryMutex.RLock()
 	var orphans []*Context
 	for _, c := range v.contextRegistry {
-		if !c.sseConnected.Load() && now.Sub(c.createdAt) > ttl {
-			orphans = append(orphans, c)
+		if c.sseConnected.Load() {
+			continue
+		}
+		if dc := c.sseDisconnectedAt.Load(); dc != nil {
+			// SSE was connected then dropped — reap if gone too long
+			if now.Sub(*dc) > ttl {
+				orphans = append(orphans, c)
+			}
+		} else {
+			// SSE never connected — reap based on creation time
+			if now.Sub(c.createdAt) > ttl {
+				orphans = append(orphans, c)
+			}
 		}
 	}
 	v.contextRegistryMutex.RUnlock()
@@ -624,7 +635,19 @@ func New() *V {
 		// use last-event-id to tell if request is a sse reconnect
 		sse.Send(datastar.EventTypePatchElements, []string{}, datastar.WithSSEEventId("via"))
 
+		// Drain stale patches on reconnect so the client gets fresh state
+		if c.sseDisconnectedAt.Load() != nil {
+			for {
+				select {
+				case <-c.patchChan:
+				default:
+					goto drained
+				}
+			}
+		drained:
+		}
 		c.sseConnected.Store(true)
+		c.sseDisconnectedAt.Store(nil)
 		v.logDebug(c, "SSE connection established")
 
 		go c.Sync()
@@ -633,7 +656,9 @@ func New() *V {
 			select {
 			case <-sse.Context().Done():
 				v.logDebug(c, "SSE connection ended")
-				v.cleanupCtx(c)
+				c.sseConnected.Store(false)
+				now := time.Now()
+				c.sseDisconnectedAt.Store(&now)
 				return
 			case <-c.ctxDisposedChan:
 				v.logDebug(c, "context disposed, closing SSE")