feat(server): keep monitors and in-flight runs going when a licence lapses

Monitor execution and the workflow runner are deliberately unguarded: billing
state must not take away a customer's ability to know their infrastructure is
on fire, and killing a run midway leaves a half-configured server.

The plan called for a server-limit check in gRPC Register. Left out: a server
row only comes from CreateServer, which already checks the cap, so counting in
Register counts the caller itself and would reject a legitimate agent at
exactly the cap.

server/internal/grpc/server.go

@@ -26,6 +26,16 @@ type vantageServer struct {
 	pb.UnimplementedVantageServer
 }
 
+// Register carries no licence check, deliberately.
+//
+// A server row only ever comes from CreateServer, which checks the cap before
+// issuing a pre-registration token. By the time an agent calls Register its row
+// already exists, so counting here would count the caller itself: an instance
+// sitting exactly at its cap would reject the very agent it just authorised, and
+// every re-registration after a reinstall would fail too.
+//
+// The cap is enforced where rows are created, which is the only place it can be
+// enforced correctly.
 func (s *vantageServer) Register(ctx context.Context, req *pb.RegisterRequest) (*pb.RegisterResponse, error) {
 	agentToken, err := services.RegisterServer(req.ServerId, req.PreRegToken, req.Hostname, req.IpAddress, req.OsInfo)
 	if err != nil {

server/internal/monitorsched/scheduler.go

@@ -27,6 +27,11 @@ func loop(ctx context.Context) {
 	active := map[string]*runner{}
 	var mu sync.Mutex
 
+	// Monitors run regardless of licence state, deliberately.
+	//
+	// A customer whose card failed must not lose the ability to know their
+	// infrastructure is on fire. Creating and editing monitors is blocked by the
+	// API gate; executing the ones that already exist is not.
 	sync := func() {
 		monitors, err := services.ListServerScheduledMonitors()
 		if err != nil {

server/internal/services/workflow_runner.go

@@ -202,6 +202,9 @@ func runServer(instanceID, runID string, srvIdx int, steps []models.ResolvedStep
 	allSecrets := map[string]string{}
 	serverFailed := false
 
+	// A run already in flight when the licence expires finishes its remaining
+	// steps. New runs are blocked at the API, but killing a workflow midway leaves
+	// a server in a half-configured state, which is worse than letting it complete.
 	for i, step := range steps {
 		startStep(runID, serverID, i, "running")
 		stepStart := time.Now()