diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/FlowDebugCommands.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/FlowDebugCommands.cs
index 42e89448..2d364033 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/FlowDebugCommands.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/FlowDebugCommands.cs
@@ -61,6 +61,11 @@ public record FlowDebugReplayCommand(Guid ExecutionId);
 /// <param name="Truncated">True when the inline event list was capped (the audit rows remain complete).</param>
 /// <param name="StartedAtUtc">When the run started.</param>
 /// <param name="FinishedAtUtc">When the run finished (or the replay was served).</param>
+/// <param name="LogsTruncated">
+/// Step-logs (D7, 2026-09-09): true when the inline <c>FlowTraceCollector</c> dropped one
+/// or more low-priority <c>ScriptLog</c> rows to protect room for step rows — the run's log lines
+/// are incomplete inline, but Replay (which reads the audit store, never truncated) is complete.
+/// </param>
 public record FlowDebugRunResult(
     Guid RootExecutionId,
     bool Completed,
@@ -69,4 +74,5 @@ public record FlowDebugRunResult(
     IReadOnlyList<AuditEvent> Events,
     bool Truncated,
     DateTimeOffset StartedAtUtc,
-    DateTimeOffset FinishedAtUtc);
+    DateTimeOffset FinishedAtUtc,
+    bool LogsTruncated = false);
diff --git a/src/ZB.MOM.WW.ScadaBridge.ManagementService/FlowDebug/FlowDebugRunner.cs b/src/ZB.MOM.WW.ScadaBridge.ManagementService/FlowDebug/FlowDebugRunner.cs
index 1d964416..4498615b 100644
--- a/src/ZB.MOM.WW.ScadaBridge.ManagementService/FlowDebug/FlowDebugRunner.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.ManagementService/FlowDebug/FlowDebugRunner.cs
@@ -188,6 +188,7 @@ public sealed class FlowDebugRunner
             executionId: root,
             durationMs: (int)Math.Min(sw.ElapsedMilliseconds, int.MaxValue),
             errorMessage: result.ErrorMessage,
+            errorDetail: result.ErrorDetail,
             requestSummary: requestJson,
             responseSummary: result.ResultJson,
             extra: new ScriptTraceExtra { Source = SourceTag }.ToJson());
@@ -212,7 +213,7 @@ public sealed class FlowDebugRunner
 
         return new FlowDebugRunResult(
             root, result.Success, result.ErrorMessage, result.Success ? null : result.ErrorCode,
-            ordered, Truncated: collector.Truncated, startedAt, finishedAt);
+            ordered, Truncated: collector.Truncated, startedAt, finishedAt, LogsTruncated: collector.LogsTruncated);
     }
 
     /// <summary>
@@ -397,7 +398,8 @@ public sealed class FlowDebugRunner
         return new FlowDebugRunResult(
             root, response.Success, response.ErrorMessage,
             response.Success ? null : faultCode ?? CallFailedCode,
-            ordered, Truncated: collector.Truncated, startedAt, DateTimeOffset.UtcNow);
+            ordered, Truncated: collector.Truncated, startedAt, DateTimeOffset.UtcNow,
+            LogsTruncated: collector.LogsTruncated);
     }
 
     /// <summary>
diff --git a/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/FlowDebugRunnerTests.cs b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/FlowDebugRunnerTests.cs
index 67d31354..d88d703d 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/FlowDebugRunnerTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/FlowDebugRunnerTests.cs
@@ -152,6 +152,30 @@ public class FlowDebugRunnerTests
         Assert.Same(siteRun, result.Events[2]);
     }
 
+    [Fact]
+    public async Task RunMethod_ScriptThrows_InboundRowCarriesErrorDetail()
+    {
+        // Step-logs D3: InboundScriptExecutor turns an unhandled script exception into a
+        // SCRIPT_ERROR InboundScriptResult whose ErrorDetail is the exception's own ToString() —
+        // never surfaced to the HTTP caller, but the Flow Debugger's inbound node reads it off
+        // the written audit row.
+        var method = new ApiMethod("M", "x") { Id = 21, TimeoutSeconds = 5 };
+        _apiRepo.GetApiMethodByIdAsync(21, Arg.Any<CancellationToken>()).Returns(method);
+        _executor.RegisterHandler("M", _ => throw new InvalidOperationException("boom"));
+
+        var result = await Runner().RunMethodAsync(_services.BuildServiceProvider(),
+            new FlowDebugRunMethodCommand(21, null), Deployer, CancellationToken.None);
+
+        Assert.False(result.Completed);
+        Assert.Equal("SCRIPT_ERROR", result.ErrorCode);
+        var inbound = Assert.Single(_central, e => e.AsRow().Kind == AuditKind.InboundRequest).AsRow();
+        Assert.NotNull(inbound.ErrorDetail);
+        Assert.StartsWith("System.InvalidOperationException: boom", inbound.ErrorDetail);
+        // The returned copy carries the same detail (redacted, same as every other field).
+        var returnedInbound = result.Events[0].AsRow();
+        Assert.StartsWith("System.InvalidOperationException: boom", returnedInbound.ErrorDetail);
+    }
+
     [Fact]
     public async Task RunMethod_UnknownMethod_IsNotFound()
     {
@@ -389,6 +413,12 @@ public class FlowDebugRunnerTests
             executionId: Guid.NewGuid(), target: "work") with
         { DetailsJson = detailsJson };
 
+    /// <summary>A <c>ScriptLog</c> row — the low-priority lane <see cref="FlowStepProjector.IsLogLine"/> recognizes.</summary>
+    private static AuditEvent LogRow() =>
+        ScadaBridgeAuditEventFactory.Create(
+            AuditChannel.ScriptTrace, AuditKind.ScriptLog, AuditStatus.Delivered,
+            executionId: Guid.NewGuid(), target: "work");
+
     [Fact]
     public async Task RunMethod_SinkEvents_AreRedacted_WhenARedactorIsRegistered()
     {
@@ -454,6 +484,37 @@ public class FlowDebugRunnerTests
 
         Assert.True(result.Truncated);
         Assert.Equal(501, result.Events.Count); // inbound row + the 500 kept
+        Assert.False(result.LogsTruncated); // these are full-priority step rows, not log lines
+    }
+
+    [Fact]
+    public async Task RunMethod_NoLogRows_LogsTruncatedIsFalse()
+    {
+        WireSinkPushingMethod(33, [TraceRow("{}")]);
+
+        var result = await Runner().RunMethodAsync(_services.BuildServiceProvider(),
+            new FlowDebugRunMethodCommand(33, null), Deployer, CancellationToken.None);
+
+        Assert.True(result.Completed, result.Error);
+        Assert.False(result.LogsTruncated);
+        Assert.False(result.Truncated);
+    }
+
+    [Fact]
+    public async Task RunMethod_OverLowPriorityReserve_ReportsLogsTruncated_ButNotTruncated()
+    {
+        // FlowTraceCollector reserves the last LowPriorityReserveEvents (50) of DefaultMaxEvents
+        // (500) for full-priority step rows — a low-priority (ScriptLog) Add stops at 450 and
+        // sets LogsTruncated, leaving Truncated (the step-row fidelity signal) untouched.
+        WireSinkPushingMethod(34, Enumerable.Range(0, 451).Select(_ => LogRow()).ToList());
+
+        var result = await Runner().RunMethodAsync(_services.BuildServiceProvider(),
+            new FlowDebugRunMethodCommand(34, null), Deployer, CancellationToken.None);
+
+        Assert.True(result.Completed, result.Error);
+        Assert.True(result.LogsTruncated);
+        Assert.False(result.Truncated);
+        Assert.Equal(451, result.Events.Count); // inbound row + the 450 log rows kept
     }
 
     // --- Flow Debugger script entry (design 2026-09-08) ---