Implement routing table snapshotter with automatic loading on startup

- Create snapshotter package with periodic (10 min) and on-demand snapshots
- Add JSON serialization with gzip compression and atomic file writes
- Update routing table to track AddedAt time for each route
- Load snapshots on startup, filtering out stale routes (>30 minutes old)
- Add ROUTEWATCH_DISABLE_SNAPSHOTTER env var for tests
- Use OS-appropriate state directories (macOS: ~/Library/Application Support, Linux: /var/lib or XDG_STATE_HOME)

internal/routewatch/app.go

@@ -14,6 +14,7 @@ import (
 	"git.eeqj.de/sneak/routewatch/internal/metrics"
 	"git.eeqj.de/sneak/routewatch/internal/routingtable"
 	"git.eeqj.de/sneak/routewatch/internal/server"
+	"git.eeqj.de/sneak/routewatch/internal/snapshotter"
 	"git.eeqj.de/sneak/routewatch/internal/streamer"
 
 	"go.uber.org/fx"
@@ -54,13 +55,14 @@ type RouteWatch struct {
 	routingTable *routingtable.RoutingTable
 	streamer     *streamer.Streamer
 	server       *server.Server
+	snapshotter  *snapshotter.Snapshotter
 	logger       *slog.Logger
 	maxRuntime   time.Duration
 }
 
 // New creates a new RouteWatch instance
 func New(deps Dependencies) *RouteWatch {
-	return &RouteWatch{
+	rw := &RouteWatch{
 		db:           deps.DB,
 		routingTable: deps.RoutingTable,
 		streamer:     deps.Streamer,
@@ -68,6 +70,19 @@ func New(deps Dependencies) *RouteWatch {
 		logger:       deps.Logger,
 		maxRuntime:   deps.Config.MaxRuntime,
 	}
+
+	// Create snapshotter unless disabled (for tests)
+	if os.Getenv("ROUTEWATCH_DISABLE_SNAPSHOTTER") != "1" {
+		snapshotter, err := snapshotter.New(deps.RoutingTable, deps.Logger)
+		if err != nil {
+			deps.Logger.Error("Failed to create snapshotter", "error", err)
+			// Continue without snapshotter
+		} else {
+			rw.snapshotter = snapshotter
+		}
+	}
+
+	return rw
 }
 
 // Run starts the RouteWatch application
@@ -97,6 +112,11 @@ func (rw *RouteWatch) Run(ctx context.Context) error {
 	// Start periodic routing table stats logging
 	go rw.logRoutingTableStats(ctx)
 
+	// Start snapshotter if available
+	if rw.snapshotter != nil {
+		rw.snapshotter.Start(ctx)
+	}
+
 	// Start streaming
 	if err := rw.streamer.Start(); err != nil {
 		return err
@@ -131,6 +151,13 @@ func (rw *RouteWatch) Run(ctx context.Context) error {
 		"duration", time.Since(metrics.ConnectedSince),
 	)
 
+	// Take final snapshot before shutdown if snapshotter is available
+	if rw.snapshotter != nil {
+		if err := rw.snapshotter.Shutdown(); err != nil {
+			rw.logger.Error("Failed to shutdown snapshotter", "error", err)
+		}
+	}
+
 	return nil
 }
 
@@ -199,10 +226,7 @@ func getModule() fx.Option {
 			),
 			routingtable.New,
 			streamer.New,
-			fx.Annotate(
-				server.New,
-				fx.ParamTags(``, ``, ``, ``),
-			),
+			server.New,
 			New,
 		),
 	)