feat(inbound-api): method-script exception detail on the inbound audit row, never on the HTTP body (D3)

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

@@ -599,8 +599,12 @@ public class InboundScriptExecutor
         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", "SCRIPT_ERROR");
+            // Safe error message, no internal details — the caller only ever sees this.
+            // Flow Debugger step logs (design 2026-09-09 D3): the exception itself rides the
+            // additive ErrorDetail so the endpoint can put it on the inbound AUDIT row, where
+            // the Flow Debugger's inbound node reads it. It must never reach the HTTP body.
+            return new InboundScriptResult(
+                false, null, "Internal script error", "SCRIPT_ERROR", ErrorDetail: ex.ToString());
         }
         finally
         {
@@ -743,8 +747,18 @@ public class InboundScriptContext
 /// <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>
+/// <param name="ErrorDetail">
+/// Flow Debugger step logs (design 2026-09-09 D3): verbose, operator-only failure detail —
+/// the method script's exception <c>ToString()</c>. <b>Audit-row only.</b> The endpoint stashes
+/// it on <c>HttpContext.Items[AuditWriteMiddleware.ErrorDetailItemKey]</c> so it lands on the
+/// inbound audit row (and therefore on the Flow Debugger's inbound node); it is NEVER written
+/// to the HTTP response, which keeps carrying the sanitised <see cref="ErrorMessage"/>. Null
+/// for failures whose message already says everything (timeouts, client aborts, site-scope
+/// denials, compile failures).
+/// </param>
 public record InboundScriptResult(
     bool Success,
     string? ResultJson,
     string? ErrorMessage,
-    string? ErrorCode = null);
+    string? ErrorCode = null,
+    string? ErrorDetail = null);