Add ECS Fargate burst seeder fleet with BGP hints and spread-kit exports.

server/internal/spreadrouter/router_test.go

@@ -123,6 +123,25 @@ func TestBuildSetsErasureLanesFlag(t *testing.T) {
 	}
 }
 
+func TestBuildSetsPreferFargateSeederWhenBurstActive(t *testing.T) {
+	in := Input{
+		TargetSubnets:      []string{"10.9.8"},
+		FargateBurstActive: true,
+		FleetAgents: []FleetAgentSnapshot{
+			{AgentID: "a1", Subnet: "10.9.8", Clearance: clearance.L2, Connected: true},
+		},
+	}
+	rt := Build(in)
+	rec, ok := rt.Recommend("10.9.8")
+	if !ok || !rec.PreferFargateSeeder {
+		t.Fatalf("route=%+v ok=%v", rec, ok)
+	}
+	hint := ToHint(rec)
+	if hint == nil || !hint.PreferFargateSeeder {
+		t.Fatalf("hint=%+v", hint)
+	}
+}
+
 func TestToHint(t *testing.T) {
 	hint := ToHint(RouteRecommendation{
 		TargetSubnet: "10.1.2", SeedAgentID: "a1", EgressAgentID: "a1", Score: 0.8,