diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/FlowDebugService.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/FlowDebugService.cs
index 05aee3a1..d06936fb 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/FlowDebugService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/FlowDebugService.cs
@@ -75,13 +75,6 @@ public sealed class FlowDebugService : IFlowDebugService
     /// <summary>Upper bound on the template parent chain the script resolver walks (cycle guard).</summary>
     private const int MaxTemplateChain = 16;
 
-    /// <summary>
-    /// Ask-sizing fallback for a call-kind script that declares no timeout of its own — mirrors
-    /// <c>SiteRuntimeOptions.ScriptExecutionTimeoutSeconds</c>, the site default the run would
-    /// actually be bounded by (the UI has no site options to read it from).
-    /// </summary>
-    private const int DefaultScriptTimeoutSeconds = 30;
-
     private static readonly JsonSerializerOptions ResultJsonOptions = new()
     {
         PropertyNameCaseInsensitive = true,
@@ -244,14 +237,15 @@ public sealed class FlowDebugService : IFlowDebugService
     {
         // The server re-resolves the script and never trusts a client-supplied trigger kind
         // (design 2026-09-08 §2); the kind is read here only to size the Ask wait — a call kind
-        // is bounded by the script's own execution timeout, a write kind by the trigger-wait
-        // window. An unresolvable script falls back to the write-kind wait, which is the longer
-        // of the two for a default-timeout script.
+        // is bounded by the script's own execution timeout — falling back to the runner's own
+        // FlowDebugRunner.DefaultScriptTimeoutSeconds so client and server agree on the bound —
+        // a write kind by the trigger-wait window. An unresolvable script falls back
+        // to the write-kind wait, which is the longer of the two for a default-timeout script.
         var command = new FlowDebugRunScriptCommand(instanceId, scriptName, parameters, value);
         var option = (await GetInstanceScriptsAsync(instanceId, cancellationToken))
             .FirstOrDefault(o => o.CanonicalName.Equals(scriptName, StringComparison.OrdinalIgnoreCase));
         var timeout = option is { IsWriteKind: false }
-            ? RunAskTimeoutFor(option.ExecutionTimeoutSeconds ?? DefaultScriptTimeoutSeconds)
+            ? RunAskTimeoutFor(option.ExecutionTimeoutSeconds ?? FlowDebugRunner.DefaultScriptTimeoutSeconds)
             : ValueChangeAskTimeoutFor(command.WaitSeconds);
 
         return await SendAndBuildAsync(command, timeout, cancellationToken);
@@ -411,8 +405,10 @@ public sealed class FlowDebugService : IFlowDebugService
     /// Loads an instance's scripts from its flattened configuration (design 2026-09-08 §2) —
     /// canonical names, effective trigger kinds and effective parameter definitions, i.e. exactly
     /// what the site's Instance Actor keys on — memoised for the life of this scoped service.
-    /// Returns null when the instance does not exist or the flatten failed; a flatten failure is
-    /// a debug-level note, never a page error, because the picker simply has nothing to offer.
+    /// Returns null when the instance does not exist (Debug — an id from a stale link) or the
+    /// flatten failed (Warning — the same severity <c>DeploymentService</c> and the Configure
+    /// page give it, since the instance could not be deployed either). Neither is a page error:
+    /// the picker simply has no scripts to offer.
     /// </summary>
     private async Task<InstanceScripts?> LoadScriptsAsync(int instanceId, CancellationToken ct)
     {
@@ -426,7 +422,9 @@ public sealed class FlowDebugService : IFlowDebugService
         var flattened = await _pipeline.FlattenAndValidateAsync(instance.Id, ct, validateScripts: false);
         if (flattened.IsFailure)
         {
-            _logger.LogDebug("Flow Debugger could not flatten instance {InstanceId}: {Error}", instanceId, flattened.Error);
+            _logger.LogWarning(
+                "Flow Debugger could not flatten instance {InstanceId} ({UniqueName}): {Error}",
+                instanceId, instance.UniqueName, flattened.Error);
             return null;
         }
 
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Services/FlowDebugServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Services/FlowDebugServiceTests.cs
index 535da2ac..aa8c5230 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Services/FlowDebugServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Services/FlowDebugServiceTests.cs
@@ -371,6 +371,8 @@ public sealed class FlowDebugServiceTests : IDisposable
         Assert.Equal(2, _received.Count);
         var vcCmd = Assert.IsType<FlowDebugRunScriptCommand>(_received[0].Command);
         Assert.Equal((7, "OnSpeed", "42"), (vcCmd.InstanceId, vcCmd.ScriptName, vcCmd.Value));
+        // A write kind fires through the attribute, so it carries no parameters.
+        Assert.Null(vcCmd.Parameters);
         var rpCmd = Assert.IsType<FlowDebugReplayCommand>(_received[1].Command);
         Assert.Equal(exec, rpCmd.ExecutionId);
     }
@@ -607,13 +609,36 @@ public sealed class FlowDebugServiceTests : IDisposable
         WireFlattened(9, "Sim01", new ResolvedScript { CanonicalName = "Manual", Code = "x", TriggerType = "Call", ExecutionTimeoutSeconds = 40 });
         var raw = new FlowDebugRunResult(Guid.NewGuid(), true, null, null, [], false, DateTimeOffset.UtcNow, DateTimeOffset.UtcNow);
         var svc = CreateService(reply: new ManagementSuccess("c", JsonSerializer.Serialize(raw, ServerJson)));
+        using var doc = JsonDocument.Parse("""{"n":3}""");
 
-        var outcome = await svc.RunScriptAsync(9, "Manual", null, null);
+        var outcome = await svc.RunScriptAsync(9, "Manual", doc.RootElement.Clone(), null);
 
         Assert.True(outcome.Success, outcome.Error);
         var env = Assert.Single(_received);
         var cmd = Assert.IsType<FlowDebugRunScriptCommand>(env.Command);
         Assert.Equal((9, "Manual"), (cmd.InstanceId, cmd.ScriptName));
+        // A call kind carries its parameters verbatim and no value.
+        Assert.Equal(3, cmd.Parameters!.Value.GetProperty("n").GetInt32());
+        Assert.Null(cmd.Value);
+    }
+
+    /// <summary>
+    /// The picker, the prediction and the run of one instance share ONE flatten for the life of
+    /// the scoped service (design 2026-09-08 §5) — a regression here means every keystroke on the
+    /// page re-walks the template chain.
+    /// </summary>
+    [Fact]
+    public async Task GetInstanceScripts_ThenPredict_ThenRun_FlattenOnce()
+    {
+        WireFlattened(9, "Sim01", new ResolvedScript { CanonicalName = "Manual", Code = "x", TriggerType = "Call" });
+        var raw = new FlowDebugRunResult(Guid.NewGuid(), true, null, null, [], false, DateTimeOffset.UtcNow, DateTimeOffset.UtcNow);
+        var svc = CreateService(reply: new ManagementSuccess("c", JsonSerializer.Serialize(raw, ServerJson)));
+
+        await svc.GetInstanceScriptsAsync(9);
+        await svc.PredictScriptAsync(9, "Manual");
+        await svc.RunScriptAsync(9, "Manual", null, null);
+
+        await _pipeline.Received(1).FlattenAndValidateAsync(9, Arg.Any<CancellationToken>(), false, null);
     }
 
     private sealed class StubAuth : AuthenticationStateProvider