feat(triggers): add Expression to the script & alarm trigger codecs

src/ScadaLink.CentralUI/Components/Shared/AlarmTriggerConfigCodec.cs

@@ -93,6 +93,10 @@ internal static class AlarmTriggerConfigCodec
                     model.HiMessage = TryReadString(root, "hiMessage");
                     model.HiHiMessage = TryReadString(root, "hiHiMessage");
                     break;
+
+                case AlarmTriggerType.Expression:
+                    model.Expression = TryReadString(root, "expression");
+                    break;
             }
         }
         catch (JsonException)
@@ -105,8 +109,10 @@ internal static class AlarmTriggerConfigCodec
 
     /// <summary>
     /// Serializes the model to the JSON shape AlarmActor.ParseEvalConfig
-    /// expects. Always writes <c>attributeName</c> (canonical key) and only
+    /// expects. Writes <c>attributeName</c> (canonical key) for the
-    /// the keys relevant to the current trigger type.
+    /// attribute-bound trigger types and only the keys relevant to the
+    /// current trigger type. <c>Expression</c> is not bound to a single
+    /// attribute, so <c>attributeName</c> is omitted for it.
     /// </summary>
     internal static string Serialize(AlarmTriggerModel model, AlarmTriggerType type)
     {
@@ -114,6 +120,7 @@ internal static class AlarmTriggerConfigCodec
         using (var w = new Utf8JsonWriter(stream))
         {
             w.WriteStartObject();
+            if (type != AlarmTriggerType.Expression)
                 w.WriteString("attributeName", model.AttributeName ?? "");
 
             switch (type)
@@ -155,6 +162,10 @@ internal static class AlarmTriggerConfigCodec
                     if (!string.IsNullOrEmpty(model.HiMessage)) w.WriteString("hiMessage", model.HiMessage);
                     if (!string.IsNullOrEmpty(model.HiHiMessage)) w.WriteString("hiHiMessage", model.HiHiMessage);
                     break;
+
+                case AlarmTriggerType.Expression:
+                    w.WriteString("expression", model.Expression ?? "");
+                    break;
             }
 
             w.WriteEndObject();
@@ -241,4 +252,7 @@ internal sealed class AlarmTriggerModel
     public string? LoMessage { get; set; }
     public string? HiMessage { get; set; }
     public string? HiHiMessage { get; set; }
+
+    // Expression — boolean C# expression evaluated on attribute updates.
+    public string? Expression { get; set; }
 }

src/ScadaLink.CentralUI/Components/Shared/ScriptTriggerConfigCodec.cs

@@ -10,7 +10,7 @@ namespace ScadaLink.CentralUI.Components.Shared;
 /// trigger; <see cref="Unknown"/> is a stored trigger-type string the runtime
 /// does not recognize (preserved as-is by the editor).
 /// </summary>
-internal enum ScriptTriggerKind { None, Interval, ValueChange, Conditional, Call, Unknown }
+internal enum ScriptTriggerKind { None, Interval, ValueChange, Conditional, Call, Expression, Unknown }
 
 /// <summary>A script's trigger as the editor emits it: a type string + config JSON.</summary>
 public sealed record ScriptTriggerValue(string? TriggerType, string? Config);
@@ -29,6 +29,9 @@ internal sealed class ScriptTriggerModel
 
     /// <summary>Comparison threshold (Conditional).</summary>
     public double? Threshold { get; set; }
+
+    /// <summary>Boolean C# expression (Expression).</summary>
+    public string? Expression { get; set; }
 }
 
 /// <summary>
@@ -59,6 +62,7 @@ internal static class ScriptTriggerConfigCodec
             "valuechange" => ScriptTriggerKind.ValueChange,
             "conditional" => ScriptTriggerKind.Conditional,
             "call" => ScriptTriggerKind.Call,
+            "expression" => ScriptTriggerKind.Expression,
             _ => ScriptTriggerKind.Unknown
         };
     }
@@ -70,6 +74,7 @@ internal static class ScriptTriggerConfigCodec
         ScriptTriggerKind.ValueChange => "ValueChange",
         ScriptTriggerKind.Conditional => "Conditional",
         ScriptTriggerKind.Call => "Call",
+        ScriptTriggerKind.Expression => "Expression",
         _ => null
     };
 
@@ -104,6 +109,10 @@ internal static class ScriptTriggerConfigCodec
                     model.Operator = NormalizeOperator(op);
                     model.Threshold = TryReadDouble(root, "threshold") ?? TryReadDouble(root, "value");
                     break;
+
+                case ScriptTriggerKind.Expression:
+                    model.Expression = root.TryGetProperty("expression", out var e) ? e.GetString() : null;
+                    break;
             }
         }
         catch (JsonException)
@@ -144,6 +153,10 @@ internal static class ScriptTriggerConfigCodec
                         w.WriteNumber("threshold", model.Threshold.Value);
                     break;
 
+                case ScriptTriggerKind.Expression:
+                    w.WriteString("expression", model.Expression ?? "");
+                    break;
+
                 // Call → empty object.
             }
             w.WriteEndObject();

src/ScadaLink.Commons/Types/Enums/AlarmTriggerType.cs

@@ -11,5 +11,11 @@ public enum AlarmTriggerType
     /// may carry its own priority; transitions between levels emit a fresh
     /// AlarmStateChanged with the corresponding <see cref="AlarmLevel"/>.
     /// </summary>
-    HiLo
+    HiLo,
+
+    /// <summary>
+    /// Read-only boolean C# expression evaluated on attribute updates. The
+    /// trigger fires when the expression evaluates to <c>true</c>.
+    /// </summary>
+    Expression
 }