2 files changed, 70 insertions, 10 deletions
diff --git a/src/Agent.App/Logging/McpHostLogObserver.cs b/src/Agent.App/Logging/McpHostLogObserver.cs
index b1410e8..37f32ec 100644
--- a/src/Agent.App/Logging/McpHostLogObserver.cs
+++ b/src/Agent.App/Logging/McpHostLogObserver.cs
@@ -3,16 +3,22 @@ using System.Text.Json;
 using Agent.Core.Localization;
 using Agent.Mcp;
 using System.Collections.Concurrent;
+using System.Threading.Channels;
 
 namespace Agent.App.Logging;
 
 public sealed class McpHostLogObserver : IMcpHostObserver, IDisposable
 {
+    private const int QueueCapacity = 4096;
     private readonly RollingFileLog _application;
     private readonly RollingFileWriter? _http;
     private readonly LocaleCatalog _locale;
     private readonly string _logDirectory;
     private readonly ConcurrentDictionary<string, byte> _observedConnections = new(StringComparer.Ordinal);
+    private readonly Channel<Action> _queue;
+    private readonly Task _writerTask;
+    private long _droppedEntries;
+    private int _disposed;
 
     public McpHostLogObserver(RollingFileLog application, LocaleCatalog locale, string logDirectory,
         bool httpRequests, long maxBytes, int retainedFiles)
@@ -21,6 +27,14 @@ public sealed class McpHostLogObserver : IMcpHostObserver, IDisposable
         _locale = locale;
         _logDirectory = logDirectory;
         if (httpRequests) _http = new RollingFileWriter(Path.Combine(logDirectory, "http.jsonl"), maxBytes, retainedFiles);
+        _queue = Channel.CreateBounded<Action>(new BoundedChannelOptions(QueueCapacity)
+        {
+            SingleReader = true,
+            SingleWriter = false,
+            FullMode = BoundedChannelFullMode.Wait,
+            AllowSynchronousContinuations = false
+        });
+        _writerTask = Task.Run(WriteLoopAsync);
     }
 
     public void Ready(McpReadyInfo info)
@@ -35,21 +49,21 @@ public sealed class McpHostLogObserver : IMcpHostObserver, IDisposable
             {
                 ["protocol"] = info.ProtocolVersion, ["pid"] = info.ProcessId, ["logs"] = _logDirectory
             });
-        _application.Operational(message);
+        Enqueue(() => _application.Operational(message));
     }
 
     public void HttpRequestStarted(McpHttpRequestStartInfo info)
     {
         if (_observedConnections.TryAdd(info.ConnectionId, 0))
-            _application.Information($"HTTP connection observed connection={info.ConnectionId} remote={info.RemoteIp}:{info.RemotePort}");
-        _application.Information($"HTTP request started connection={info.ConnectionId} trace={info.TraceId} remote={info.RemoteIp}:{info.RemotePort} method={info.Method} path={info.Path}");
+            Enqueue(() => _application.Information($"HTTP connection observed connection={info.ConnectionId} remote={info.RemoteIp}:{info.RemotePort}"));
+        Enqueue(() => _application.Information($"HTTP request started connection={info.ConnectionId} trace={info.TraceId} remote={info.RemoteIp}:{info.RemotePort} method={info.Method} path={info.Path}"));
     }
 
     public void HttpRequest(McpHttpRequestInfo info)
     {
-        _application.Information(string.Create(CultureInfo.InvariantCulture,
-            $"HTTP request completed connection={info.ConnectionId} remote={info.RemoteIp}:{info.RemotePort} method={info.Method} path={info.Path} status={info.Status} duration_ms={info.DurationMs:F3}"));
-        _http?.WriteLine(JsonSerializer.Serialize(new
+        string applicationLine = string.Create(CultureInfo.InvariantCulture,
+            $"HTTP request completed connection={info.ConnectionId} remote={info.RemoteIp}:{info.RemotePort} method={info.Method} path={info.Path} status={info.Status} duration_ms={info.DurationMs:F3}");
+        string? httpLine = _http is null ? null : JsonSerializer.Serialize(new
         {
             timestamp = info.Timestamp,
             connection_id = info.ConnectionId,
@@ -68,9 +82,53 @@ public sealed class McpHostLogObserver : IMcpHostObserver, IDisposable
             mcp_protocol_version = NullIfEmpty(info.ProtocolVersion),
             mcp_method = NullIfEmpty(info.McpMethod),
             mcp_name = NullIfEmpty(info.McpName)
-        }));
+        });
+        Enqueue(() =>
+        {
+            if (httpLine is not null) _http!.WriteLine(httpLine);
+            _application.Information(applicationLine);
+        });
+    }
+
+    private void Enqueue(Action write)
+    {
+        if (Volatile.Read(ref _disposed) != 0) return;
+        if (!_queue.Writer.TryWrite(write)) Interlocked.Increment(ref _droppedEntries);
+    }
+
+    private async Task WriteLoopAsync()
+    {
+        try
+        {
+            await foreach (Action write in _queue.Reader.ReadAllAsync().ConfigureAwait(false))
+            {
+                try { write(); }
+                catch (Exception ex) when (ex is not (OutOfMemoryException or StackOverflowException or AccessViolationException))
+                {
+                    System.Diagnostics.Debug.WriteLine($"MCP observability write failed: {ex.Message}");
+                }
+
+                long dropped = Interlocked.Exchange(ref _droppedEntries, 0);
+                if (dropped > 0)
+                {
+                    try { _application.Warning($"MCP observability queue dropped {dropped} log entries."); }
+                    catch (Exception ex) when (ex is not (OutOfMemoryException or StackOverflowException or AccessViolationException))
+                    {
+                        System.Diagnostics.Debug.WriteLine($"MCP observability drop report failed: {ex.Message}");
+                    }
+                }
+            }
+        }
+        finally { _http?.Dispose(); }
     }
 
     private static string? NullIfEmpty(string? value) => string.IsNullOrWhiteSpace(value) ? null : value;
-    public void Dispose() => _http?.Dispose();
+
+    public void Dispose()
+    {
+        if (Interlocked.Exchange(ref _disposed, 1) != 0) return;
+        _queue.Writer.TryComplete();
+        try { _writerTask.Wait(TimeSpan.FromSeconds(5)); }
+        catch (AggregateException) { }
+    }
 }
diff --git a/src/Agent.App/Logging/RollingFileLog.cs b/src/Agent.App/Logging/RollingFileLog.cs
index 8bdbbb4..f471a9e 100644
--- a/src/Agent.App/Logging/RollingFileLog.cs
+++ b/src/Agent.App/Logging/RollingFileLog.cs
@@ -5,12 +5,14 @@ namespace Agent.App.Logging;
 public sealed class RollingFileLog : IDisposable
 {
     private readonly RollingFileWriter _writer;
+    private readonly TextWriter _consoleWriter;
     private readonly int _minimumLevel;
 
-    public RollingFileLog(string directory, long maxBytes, int retainedFiles, string minimumLevel = "information")
+    public RollingFileLog(string directory, long maxBytes, int retainedFiles, string minimumLevel = "information", TextWriter? consoleWriter = null)
     {
         Directory.CreateDirectory(directory);
         _writer = new RollingFileWriter(Path.Combine(directory, "application.log"), maxBytes, retainedFiles);
+        _consoleWriter = consoleWriter ?? Console.Error;
         _minimumLevel = ParseLevel(minimumLevel);
     }
 
@@ -24,7 +26,7 @@ public sealed class RollingFileLog : IDisposable
     {
         if (!force && Level(level) < _minimumLevel) return;
         string line = string.Create(CultureInfo.InvariantCulture, $"{DateTimeOffset.UtcNow:O} [{level}] {message}");
-        Console.Error.WriteLine(line);
+        _consoleWriter.WriteLine(line);
         _writer.WriteLine(line);
     }