feat(inbound-api): machine-readable error codes per spec (incl. SITE_UNREACHABLE) + 415 for non-JSON bodies

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

src/ZB.MOM.WW.ScadaBridge.InboundAPI/RouteHelper.cs

@@ -4,6 +4,22 @@ using ZB.MOM.WW.ScadaBridge.Commons.Types;
 
 namespace ZB.MOM.WW.ScadaBridge.InboundAPI;
 
+/// <summary>
+/// C3: a routed call failed because the target site could not be reached (no contact /
+/// unreachable). Derives from <see cref="InvalidOperationException"/> so existing
+/// callers that catch the base type are unaffected, while
+/// <see cref="InboundScriptExecutor"/> catches this more specific type to surface the
+/// spec's <c>SITE_UNREACHABLE</c> error code instead of a generic <c>SCRIPT_ERROR</c>.
+/// A routing failure whose message does <em>not</em> indicate unreachability stays a
+/// plain <see cref="InvalidOperationException"/>.
+/// </summary>
+public sealed class SiteUnreachableException : InvalidOperationException
+{
+    /// <summary>Initializes a new <see cref="SiteUnreachableException"/> with the given message.</summary>
+    /// <param name="message">The routing-level failure message that indicated the site was unreachable.</param>
+    public SiteUnreachableException(string message) : base(message) { }
+}
+
 /// <summary>
 /// Route.To() helper for cross-site calls from inbound API scripts.
 /// Resolves instance to site, routes via <see cref="IInstanceRouter"/>, blocks until
@@ -170,7 +186,7 @@ public class RouteTarget
 
         if (!response.Success)
         {
-            throw new InvalidOperationException(
+            throw RoutingFailure(
                 response.ErrorMessage ?? "Remote script call failed");
         }
 
@@ -218,7 +234,7 @@ public class RouteTarget
 
         if (!response.Success)
         {
-            throw new InvalidOperationException(
+            throw RoutingFailure(
                 response.ErrorMessage ?? "Remote attribute read failed");
         }
 
@@ -282,7 +298,7 @@ public class RouteTarget
 
         if (!response.Success)
         {
-            throw new InvalidOperationException(
+            throw RoutingFailure(
                 response.ErrorMessage ?? "Remote attribute wait failed");
         }
 
@@ -333,7 +349,7 @@ public class RouteTarget
 
         if (!response.Success)
         {
-            throw new InvalidOperationException(
+            throw RoutingFailure(
                 response.ErrorMessage ?? "Remote attribute write failed");
         }
     }
@@ -350,10 +366,30 @@ public class RouteTarget
         var siteId = await _instanceLocator.GetSiteIdForInstanceAsync(_instanceCode, cancellationToken);
         if (siteId == null)
         {
-            throw new InvalidOperationException(
+            // Route the site-resolution failure through the same classifier so a
+            // message indicating the site is unreachable surfaces as SITE_UNREACHABLE;
+            // a plain not-found / no-assigned-site stays a generic InvalidOperationException.
+            throw RoutingFailure(
                 $"Instance '{_instanceCode}' not found or has no assigned site");
         }
 
         return siteId;
     }
+
+    /// <summary>
+    /// C3: classifies a routing-level failure message. When the message indicates the
+    /// site could not be reached (unreachable / no contact) the failure is a
+    /// <see cref="SiteUnreachableException"/> — so <see cref="InboundScriptExecutor"/>
+    /// can surface the spec's <c>SITE_UNREACHABLE</c> code — otherwise a plain
+    /// <see cref="InvalidOperationException"/>.
+    /// </summary>
+    private static InvalidOperationException RoutingFailure(string message) =>
+        IsUnreachable(message)
+            ? new SiteUnreachableException(message)
+            : new InvalidOperationException(message);
+
+    private static bool IsUnreachable(string message) =>
+        message.Contains("unreachable", StringComparison.OrdinalIgnoreCase)
+        || message.Contains("no contact", StringComparison.OrdinalIgnoreCase)
+        || message.Contains("no-contact", StringComparison.OrdinalIgnoreCase);
 }