rules+rpcserver: handle unknown rules

This is to tolerate unknown rules sent from the autopilot for the
`autopilot features` command.

Otherwise, when trying to register a feature that requires an upgrade, a
more user friendly error is returned.

rules/manager_set.go

@@ -31,7 +31,8 @@ func (m ManagerSet) InitEnforcer(cfg Config, name string,
 
 	mgr, ok := m[name]
 	if !ok {
-		return nil, ErrUnknownRule
+		return nil, fmt.Errorf("%w %s, please upgrade", ErrUnknownRule,
+			name)
 	}
 
 	return mgr.NewEnforcer(cfg, values)
@@ -54,7 +55,8 @@ func (m ManagerSet) UnmarshalRuleValues(name string, proto *litrpc.RuleValue) (
 
 	mgr, ok := m[name]
 	if !ok {
-		return nil, ErrUnknownRule
+		return nil, fmt.Errorf("%w %s, please upgrade", ErrUnknownRule,
+			name)
 	}
 
 	return mgr.NewValueFromProto(proto)
@@ -67,7 +69,8 @@ func (m ManagerSet) InitRuleValues(name string, valueBytes []byte) (Values,
 
 	mgr, ok := m[name]
 	if !ok {
-		return nil, ErrUnknownRule
+		return nil, fmt.Errorf("%w %s, please upgrade", ErrUnknownRule,
+			name)
 	}
 
 	v := mgr.EmptyValue()

session_rpcserver.go

@@ -1348,10 +1348,13 @@ func convertRules(ruleMgr rules.ManagerSet,
 		knownRules = ruleMgr.GetAllRules()
 	)
 	for name, rule := range ruleList {
-		known := true
 		if !knownRules[name] {
 			upgrade = true
-			known = false
+			res[name] = &litrpc.RuleValues{
+				Known: false,
+			}
+
+			continue
 		}
 
 		defaultVals, err := ruleMgr.InitRuleValues(name, rule.Default)
@@ -1370,7 +1373,7 @@ func convertRules(ruleMgr rules.ManagerSet,
 		}
 
 		res[name] = &litrpc.RuleValues{
-			Known:    known,
+			Known:    true,
 			Defaults: defaultVals.ToProto(),
 			MinValue: minVals.ToProto(),
 			MaxValue: maxVals.ToProto(),