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/InboundScriptExecutor.cs

@@ -384,7 +384,7 @@ public class InboundScriptExecutor
                 // Fast-fail only when the CURRENT script text is the one already known bad.
                 if (_knownBadMethods.TryGetValue(method.Name, out var badScript)
                     && string.Equals(badScript, method.Script, StringComparison.Ordinal))
-                    return new InboundScriptResult(false, null, "Script compilation failed for this method");
+                    return new InboundScriptResult(false, null, "Script compilation failed for this method", "SCRIPT_COMPILE_FAILED");
 
                 // Lazy compile (handles methods created after startup, and stale/known-bad
                 // recompiles). Compile outside the cache so a failed compile is not stored,
@@ -396,7 +396,7 @@ public class InboundScriptExecutor
                     // Routed through TryRecordBadMethod so the
                     // cache is bounded under a flood of unique method names.
                     TryRecordBadMethod(method.Name, method.Script ?? string.Empty);
-                    return new InboundScriptResult(false, null, "Script compilation failed for this method");
+                    return new InboundScriptResult(false, null, "Script compilation failed for this method", "SCRIPT_COMPILE_FAILED");
                 }
 
                 _knownBadMethods.TryRemove(method.Name, out _);
@@ -448,17 +448,25 @@ public class InboundScriptExecutor
             if (timeoutCts.IsCancellationRequested && !cancellationToken.IsCancellationRequested)
             {
                 _logger.LogWarning("Script execution timed out for method {Method}", method.Name);
-                return new InboundScriptResult(false, null, "Script execution timed out");
+                return new InboundScriptResult(false, null, "Script execution timed out", "TIMEOUT");
             }
 
             _logger.LogDebug("Inbound API request for method {Method} cancelled by client", method.Name);
             return new InboundScriptResult(false, null, "Request cancelled by client");
         }
+        catch (SiteUnreachableException)
+        {
+            // C3: a routed Route.To(...).Call(...) reached a site that could not be
+            // contacted. Surface the machine-readable SITE_UNREACHABLE code (spec
+            // Component-InboundAPI failure body) instead of the generic SCRIPT_ERROR.
+            _logger.LogWarning("Routed site unreachable for method {Method}", method.Name);
+            return new InboundScriptResult(false, null, "Site unreachable", "SITE_UNREACHABLE");
+        }
         catch (Exception ex)
         {
             _logger.LogError(ex, "Script execution failed for method {Method}", method.Name);
             // Safe error message, no internal details
-            return new InboundScriptResult(false, null, "Internal script error");
+            return new InboundScriptResult(false, null, "Internal script error", "SCRIPT_ERROR");
         }
         finally
         {
@@ -537,7 +545,17 @@ public class InboundScriptContext
 /// <summary>
 /// Result of executing an inbound API script.
 /// </summary>
+/// <param name="Success">Whether the script executed successfully.</param>
+/// <param name="ResultJson">The serialized script return value on success; null otherwise.</param>
+/// <param name="ErrorMessage">A sanitized, caller-safe error message on failure; null on success.</param>
+/// <param name="ErrorCode">
+/// C3: an additive, machine-readable error code the endpoint surfaces in the failure
+/// body's <c>code</c> field (e.g. <c>TIMEOUT</c>, <c>SITE_UNREACHABLE</c>,
+/// <c>SCRIPT_COMPILE_FAILED</c>, <c>SCRIPT_ERROR</c>). Null when the executor does not
+/// classify the failure; the endpoint then falls back to <c>SCRIPT_ERROR</c>.
+/// </param>
 public record InboundScriptResult(
     bool Success,
     string? ResultJson,
-    string? ErrorMessage);
+    string? ErrorMessage,
+    string? ErrorCode = null);