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

tests/ZB.MOM.WW.ScadaBridge.InboundAPI.Tests/EndpointExtensionsTests.cs

@@ -432,7 +432,23 @@ public sealed class EndpointExtensionsTests : IDisposable
         var method = SeedMethod(1, "boom",
             """throw new System.InvalidOperationException("boom-msg");""");
 
-        using var host = await BuildHostAsync(method);
+        // Flow Debugger step logs (design 2026-09-09 D3): the detail the body must NOT carry
+        // is nonetheless stashed for AuditWriteMiddleware, so the inbound audit row (and the
+        // Flow Debugger's inbound node) can say why the run failed. A capture middleware reads
+        // the slot once the endpoint has finished, proving both halves in one request.
+        string? capturedDetail = null;
+        using var host = await BuildHostAsync(method, customize: builder =>
+        {
+            builder.Use(async (ctx, next) =>
+            {
+                await next();
+                if (ctx.Items.TryGetValue(
+                        AuditWriteMiddleware.ErrorDetailItemKey, out var stashed))
+                {
+                    capturedDetail = stashed as string;
+                }
+            });
+        });
         var token = await SeedKeyAsync(host, "key1", "caller", new[] { "boom" });
         var client = host.GetTestClient();
 
@@ -445,6 +461,10 @@ public sealed class EndpointExtensionsTests : IDisposable
         // message is not leaked (the executor sanitises before this point).
         Assert.Contains("error", body);
         Assert.DoesNotContain("boom-msg", body);
+
+        // …while the audit-only slot carries the real cause.
+        Assert.NotNull(capturedDetail);
+        Assert.Contains("boom-msg", capturedDetail);
     }
 
     [Fact]