fix(master): review fixes for drift restore and accept (#10)

internal/master/model/model.go

@@ -15,6 +15,8 @@ import (
 // Sentinel errors returned by storage.
 var (
 	ErrNotFound = errors.New("not found")
+	// ErrConflict means the row already exists, or that it changed meanwhile
+	// (AcceptRunning, MergeService).
 	ErrConflict = errors.New("already exists")
 	ErrRevoked  = errors.New("agent revoked")
 )
@@ -166,6 +168,11 @@ func RunningRef(actualRef, actualDigest string) string {
 	return r.String()
 }
 
+// RunningRef returns the ref accepting the running version records as the
+// desired one; see the function RunningRef. Templates post it as the guard of
+// the accept form.
+func (s Service) RunningRef() string { return RunningRef(s.ActualRef, s.ActualDigest) }
+
 // Move says that the removed service FromID has probably moved to the live
 // service ToID on another agent. The names are the agents' own; a revoked
 // agent keeps its name.