fix: restrict tieline creation when signal types are invalid

src/PepperDash.Essentials.Core/Routing/TieLine.cs

@@ -1,6 +1,6 @@
-using Newtonsoft.Json;
+using System;
-using System;
 using System.Collections.Generic;
+using Newtonsoft.Json;
 
 namespace PepperDash.Essentials.Core
 {
@@ -21,24 +21,24 @@ namespace PepperDash.Essentials.Core
         //public int InUseCount { get { return DestinationUsingThis.Count; } }
 
         /// <summary>
-        /// Gets the type of this tie line. Will either be the type of the destination port
+        /// Gets the type of this tie line. Returns the intersection of signal types supported by both 
-        /// or the type of OverrideType when it is set.
+        /// the source and destination ports (what signals can actually travel through this tie line),
+        /// or the OverrideType when it is set.
         /// </summary>
         public eRoutingSignalType Type
         {
             get
             {
                 if (OverrideType.HasValue) return OverrideType.Value;
-                return DestinationPort.Type;
+                return SourcePort.Type & DestinationPort.Type;
             }
         }
 
         /// <summary>
-        /// Use this to override the Type property for the destination port. For example,
+        /// Use this to override the Type property. For example, when both ports support AudioVideo
-        /// when the tie line is type AudioVideo, and the signal flow should be limited to
+        /// but the physical cable only carries Audio or Video, setting this will limit the signal 
-        /// Audio-only or Video only, changing this type will alter the signal paths
+        /// paths available to the routing algorithm without affecting the actual port types.
-        /// available to the routing algorithm without affecting the actual Type
+        /// When set, this value is used instead of the calculated intersection of source and destination types.
-        /// of the destination port.
         /// </summary>
         public eRoutingSignalType? OverrideType { get; set; }
 
@@ -79,7 +79,7 @@ namespace PepperDash.Essentials.Core
         /// </summary>
         /// <param name="sourcePort">The source output port.</param>
         /// <param name="destinationPort">The destination input port.</param>
-        /// <param name="overrideType">The signal type to limit the link to. Overrides DestinationPort.Type for routing calculations.</param>
+        /// <param name="overrideType">The signal type to limit the link to. Overrides the calculated intersection of port types for routing calculations.</param>
         public TieLine(RoutingOutputPort sourcePort, RoutingInputPort destinationPort, eRoutingSignalType? overrideType) :
             this(sourcePort, destinationPort)
         {
@@ -91,7 +91,7 @@ namespace PepperDash.Essentials.Core
         /// </summary>
         /// <param name="sourcePort">The source output port.</param>
         /// <param name="destinationPort">The destination input port.</param>
-        /// <param name="overrideType">The signal type to limit the link to. Overrides DestinationPort.Type for routing calculations.</param>
+        /// <param name="overrideType">The signal type to limit the link to. Overrides the calculated intersection of port types for routing calculations.</param>
         public TieLine(RoutingOutputPort sourcePort, RoutingInputPort destinationPort, eRoutingSignalType overrideType) :
             this(sourcePort, destinationPort)
         {

src/PepperDash.Essentials.Core/Routing/TieLineConfig.cs

@@ -49,7 +49,9 @@ namespace PepperDash.Essentials.Core.Config
 		public string DestinationPort { get; set; }
 
 		/// <summary>
-		/// Optional override for the signal type of the tie line. If set, this overrides the destination port's type for routing calculations.
+		/// Optional override for the signal type of the tie line. If set, this overrides the calculated 
+		/// intersection of source and destination port types for routing calculations. Useful when the 
+		/// physical cable supports fewer signal types than both ports are capable of.
 		/// </summary>
 		[JsonProperty("type", NullValueHandling = NullValueHandling.Ignore)]
 		[JsonConverter(typeof(StringEnumConverter))]
@@ -96,6 +98,32 @@ namespace PepperDash.Essentials.Core.Config
 				return null;
 			}
 
+			// Validate signal type compatibility
+			if (OverrideType.HasValue)
+			{
+				// When override type is specified, both ports must support it
+				if (!sourceOutputPort.Type.HasFlag(OverrideType.Value))
+				{
+					LogError($"Override type '{OverrideType.Value}' is not supported by source port '{SourcePort}' (type: {sourceOutputPort.Type})");
+					return null;
+				}
+
+				if (!destinationInputPort.Type.HasFlag(OverrideType.Value))
+				{
+					LogError($"Override type '{OverrideType.Value}' is not supported by destination port '{DestinationPort}' (type: {destinationInputPort.Type})");
+					return null;
+				}
+			}
+			else
+			{
+				// Without override type, ports must have at least one common signal type flag
+				if ((sourceOutputPort.Type & destinationInputPort.Type) == 0)
+				{
+					LogError($"Incompatible signal types: source port '{SourcePort}' (type: {sourceOutputPort.Type}) has no common signal types with destination port '{DestinationPort}' (type: {destinationInputPort.Type})");
+					return null;
+				}
+			}
+
 			return new TieLine(sourceOutputPort, destinationInputPort, OverrideType);
 		}