fix(auditlog): capture request/response payloads on outbound API audit rows

The outbound ApiCall emitter hard-coded RequestSummary/ResponseSummary to null,
so audited API calls carried no inputs/outputs — contrary to the Audit Log
payload-capture spec. Thread the call arguments into the sync ApiCall emitter
and the cached immediate-completion path (CachedSubmit / ApiCallCached /
CachedResolve), and stamp the response body from ExternalCallResult.ResponseJson.
The writer's payload filter still applies the size cap + redaction downstream.

The S&F retry-loop cached rows are unchanged — request data is not threaded
through the store-and-forward buffer (same boundary as SourceScript).

src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs

@@ -420,7 +420,7 @@ public class ScriptRuntimeContext
             {
                 var elapsedMs = (int)((Stopwatch.GetTimestamp() - startTicks)
                     * 1000d / Stopwatch.Frequency);
-                EmitCallAudit(systemName, methodName, occurredAtUtc, elapsedMs, result, thrown);
+                EmitCallAudit(systemName, methodName, occurredAtUtc, elapsedMs, result, thrown, parameters);
             }
         }
 
@@ -458,7 +458,7 @@ public class ScriptRuntimeContext
             // Submitted row even if the immediate-delivery attempt happens to
             // resolve before this method returns.
             await EmitCachedSubmitTelemetryAsync(
-                systemName, methodName, target, trackedId, occurredAtUtc, cancellationToken)
+                systemName, methodName, target, trackedId, occurredAtUtc, parameters, cancellationToken)
                 .ConfigureAwait(false);
 
             // Hand off to the existing cached-call path. The TrackedOperationId
@@ -503,7 +503,7 @@ public class ScriptRuntimeContext
             if (result is { WasBuffered: false })
             {
                 await EmitImmediateTerminalTelemetryAsync(
-                    systemName, methodName, target, trackedId, result, cancellationToken)
+                    systemName, methodName, target, trackedId, result, parameters, cancellationToken)
                     .ConfigureAwait(false);
             }
 
@@ -521,6 +521,7 @@ public class ScriptRuntimeContext
             string target,
             TrackedOperationId trackedId,
             DateTime occurredAtUtc,
+            IReadOnlyDictionary<string, object?>? parameters,
             CancellationToken cancellationToken)
         {
             if (_cachedForwarder == null)
@@ -544,6 +545,8 @@ public class ScriptRuntimeContext
                         SourceScript = _sourceScript,
                         Target = target,
                         Status = AuditStatus.Submitted,
+                        // Submit precedes the call — request args only, no response yet.
+                        RequestSummary = SerializeRequest(parameters),
                         ForwardState = AuditForwardState.Pending,
                     },
                     Operational: new SiteCallOperational(
@@ -599,6 +602,7 @@ public class ScriptRuntimeContext
             string target,
             TrackedOperationId trackedId,
             ExternalCallResult result,
+            IReadOnlyDictionary<string, object?>? parameters,
             CancellationToken cancellationToken)
         {
             if (_cachedForwarder == null)
@@ -653,6 +657,8 @@ public class ScriptRuntimeContext
                         Status = AuditStatus.Attempted,
                         HttpStatus = httpStatus,
                         ErrorMessage = result.Success ? null : result.ErrorMessage,
+                        RequestSummary = SerializeRequest(parameters),
+                        ResponseSummary = result.ResponseJson,
                         ForwardState = AuditForwardState.Pending,
                     },
                     Operational: new SiteCallOperational(
@@ -712,6 +718,8 @@ public class ScriptRuntimeContext
                         Status = auditTerminalStatus,
                         HttpStatus = httpStatus,
                         ErrorMessage = result.Success ? null : result.ErrorMessage,
+                        RequestSummary = SerializeRequest(parameters),
+                        ResponseSummary = result.ResponseJson,
                         ForwardState = AuditForwardState.Pending,
                     },
                     Operational: new SiteCallOperational(
@@ -762,7 +770,8 @@ public class ScriptRuntimeContext
             DateTime occurredAtUtc,
             int durationMs,
             ExternalCallResult? result,
-            Exception? thrown)
+            Exception? thrown,
+            IReadOnlyDictionary<string, object?>? parameters)
         {
             if (_auditWriter == null)
             {
@@ -772,7 +781,8 @@ public class ScriptRuntimeContext
             AuditEvent evt;
             try
             {
-                evt = BuildCallAuditEvent(systemName, methodName, occurredAtUtc, durationMs, result, thrown);
+                evt = BuildCallAuditEvent(
+                    systemName, methodName, occurredAtUtc, durationMs, result, thrown, parameters);
             }
             catch (Exception buildEx)
             {
@@ -828,7 +838,8 @@ public class ScriptRuntimeContext
             DateTime occurredAtUtc,
             int durationMs,
             ExternalCallResult? result,
-            Exception? thrown)
+            Exception? thrown,
+            IReadOnlyDictionary<string, object?>? parameters)
         {
             // Status: Delivered on a Success result; Failed otherwise (the
             // ExternalSystemClient already maps HTTP non-2xx + transient
@@ -885,13 +896,41 @@ public class ScriptRuntimeContext
                 DurationMs = durationMs,
                 ErrorMessage = errorMessage,
                 ErrorDetail = errorDetail,
-                RequestSummary = null,
-                ResponseSummary = null,
+                // Payload capture: the request arguments and the response body.
+                // The audit writer's payload filter applies the configured size
+                // cap and header/secret redaction downstream — the emitter just
+                // hands over the raw values.
+                RequestSummary = SerializeRequest(parameters),
+                ResponseSummary = result?.ResponseJson,
                 PayloadTruncated = false,
                 Extra = null,
                 ForwardState = AuditForwardState.Pending,
             };
         }
+
+        /// <summary>
+        /// Serialises the outbound-call argument dictionary into the JSON
+        /// <c>RequestSummary</c> stamped on <c>ApiOutbound</c> audit rows.
+        /// Returns <c>null</c> for a null/empty argument set. Serialization
+        /// failure is swallowed (returns <c>null</c>) — a payload that cannot be
+        /// summarised must never abort the best-effort audit emission.
+        /// </summary>
+        private static string? SerializeRequest(IReadOnlyDictionary<string, object?>? parameters)
+        {
+            if (parameters is null || parameters.Count == 0)
+            {
+                return null;
+            }
+
+            try
+            {
+                return JsonSerializer.Serialize(parameters);
+            }
+            catch (Exception)
+            {
+                return null;
+            }
+        }
     }
 
     /// <summary>

tests/ScadaLink.SiteRuntime.Tests/Scripts/ExternalSystemCachedCallEmissionTests.cs

@@ -94,6 +94,42 @@ public class ExternalSystemCachedCallEmissionTests
         Assert.Null(packet.Operational.TerminalAtUtc);
     }
 
+    [Fact]
+    public async Task CachedCall_ImmediateCompletion_CapturesRequestArgs_AndResponseBody()
+    {
+        var client = new Mock<IExternalSystemClient>();
+        client
+            .Setup(c => c.CachedCallAsync(
+                "ERP", "GetOrder",
+                It.IsAny<IReadOnlyDictionary<string, object?>?>(),
+                InstanceName,
+                It.IsAny<CancellationToken>(),
+                It.IsAny<TrackedOperationId?>()))
+            .ReturnsAsync(new ExternalCallResult(true, "{\"ok\":true}", null, WasBuffered: false));
+        var forwarder = new CapturingForwarder();
+
+        var helper = CreateHelper(client.Object, forwarder);
+        var args = new Dictionary<string, object?> { ["orderId"] = 42 };
+        await helper.CachedCall("ERP", "GetOrder", args);
+
+        // Immediate completion (WasBuffered=false) emits Submit, Attempted, Resolve.
+        Assert.Equal(3, forwarder.Telemetry.Count);
+        var submit = forwarder.Telemetry.Single(t => t.Audit.Kind == AuditKind.CachedSubmit);
+        var attempted = forwarder.Telemetry.Single(t => t.Audit.Kind == AuditKind.ApiCallCached);
+        var resolve = forwarder.Telemetry.Single(t => t.Audit.Kind == AuditKind.CachedResolve);
+
+        // Every row carries the request args; the two post-call rows also carry
+        // the response body (Submit precedes the call, so it has no response).
+        Assert.Equal("{\"orderId\":42}", submit.Audit.RequestSummary);
+        Assert.Null(submit.Audit.ResponseSummary);
+
+        Assert.Equal("{\"orderId\":42}", attempted.Audit.RequestSummary);
+        Assert.Equal("{\"ok\":true}", attempted.Audit.ResponseSummary);
+
+        Assert.Equal("{\"orderId\":42}", resolve.Audit.RequestSummary);
+        Assert.Equal("{\"ok\":true}", resolve.Audit.ResponseSummary);
+    }
+
     [Fact]
     public async Task CachedCall_ReturnsTrackedOperationId()
     {

tests/ScadaLink.SiteRuntime.Tests/Scripts/ExternalSystemCallAuditEmissionTests.cs

@@ -81,6 +81,29 @@ public class ExternalSystemCallAuditEmissionTests
         Assert.Equal(DateTimeKind.Utc, evt.OccurredAtUtc.Kind);
         Assert.NotEqual(Guid.Empty, evt.EventId);
         Assert.False(evt.PayloadTruncated);
+        // No call arguments → null request summary; the response body is captured.
+        Assert.Null(evt.RequestSummary);
+        Assert.Equal("{}", evt.ResponseSummary);
+    }
+
+    [Fact]
+    public async Task Call_CapturesRequestArgs_AndResponseBody_OnTheAuditRow()
+    {
+        var client = new Mock<IExternalSystemClient>();
+        client
+            .Setup(c => c.CallAsync("Weather", "GetCurrent", It.IsAny<IReadOnlyDictionary<string, object?>?>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new ExternalCallResult(true, "{\"tempC\":11.4}", null));
+        var writer = new CapturingAuditWriter();
+
+        var helper = CreateHelper(client.Object, writer);
+        var args = new Dictionary<string, object?> { ["city"] = "Dublin" };
+        await helper.Call("Weather", "GetCurrent", args);
+
+        var evt = Assert.Single(writer.Events);
+        // RequestSummary is the serialized argument dictionary; ResponseSummary
+        // is the verbatim response body. (Cap + redaction are the writer's job.)
+        Assert.Equal("{\"city\":\"Dublin\"}", evt.RequestSummary);
+        Assert.Equal("{\"tempC\":11.4}", evt.ResponseSummary);
     }
 
     [Fact]