Elect one fleet torrent seeder per AWS VPC via IMDS cloud_instance_meta.

Agents read vpc-id from EC2 IMDS on auth; the server scopes subnet_primary_seeder to vpc-id with /24 fallback, exposes VPC seeder badges, and documents cross-VPC gossip via peering/TGW.

server/internal/atlas/fleet_gossip_test.go

@@ -2,12 +2,15 @@ package atlas
 
 import "testing"
 
-func TestNormalizeFleetGossipShardAdvert(t *testing.T) {
-	r, ok := NormalizeFleetGossipRecord(FleetGossipRecord{
-		Kind: FleetGossipHaveShard, AgentID: "a", Token: "t", ShardHash: "h",
-		Region: "us-west-2", ShardIndex: 4,
-	})
-	if !ok || r.ShardAdvert != "us-west-2:4" {
-		t.Fatalf("advert=%q", r.ShardAdvert)
+func TestNormalizeFleetGossipRecords(t *testing.T) {
+	in := []FleetGossipRecord{
+		{Kind: FleetGossipHaveShard, AgentID: "a", Token: "tok", ShardHash: "abc"},
+		{Kind: "bogus"},
+		{Kind: FleetGossipHealthy, AgentID: "b", Healthy: true},
+		{Kind: FleetGossipKnowNode, AgentID: "a", TargetAgentID: "c"},
+	}
+	out := NormalizeFleetGossipRecords(in)
+	if len(out) != 3 {
+		t.Fatalf("got %d records", len(out))
 	}
 }