feat: add UTC timestamps to console log entries

Author: Copilot

src/Cli.Tests/CustomLoggerTests.cs

@@ -77,8 +77,8 @@ public void LogOutput_UsesAbbreviatedLogLevelLabels(LogLevel logLevel, string ex
         string actual = expectStderr ? stderr : stdout;
         string other = expectStderr ? stdout : stderr;
 
-        Assert.IsTrue(actual.StartsWith(expectedPrefix),
-            $"Expected output to start with '{expectedPrefix}' but got: '{actual}'");
+        Assert.IsTrue(actual.Contains(expectedPrefix),
+            $"Expected output to contain '{expectedPrefix}' but got: '{actual}'");
         StringAssert.Contains(actual, Message);
         Assert.AreEqual(string.Empty, other,
             $"Did not expect output on the other stream but got: '{other}'");

src/Cli/CustomLoggerProvider.cs

@@ -124,13 +124,14 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
                 // Apply colors so the abbreviation matches the visual style of engine logs.
                 // try/finally guarantees the original colors are restored even if Write throws,
                 // otherwise the console would be left tinted (e.g. red on error) for subsequent output.
+                string mcpTimestamp = DateTime.UtcNow.ToString("yyyy-MM-dd'T'HH:mm:ss.fff'Z'");
                 ConsoleColor mcpOriginalForeGroundColor = Console.ForegroundColor;
                 ConsoleColor mcpOriginalBackGroundColor = Console.BackgroundColor;
                 try
                 {
                     Console.ForegroundColor = _logLevelToForeGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.White);
                     Console.BackgroundColor = _logLevelToBackGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.Black);
-                    Console.Error.Write($"{mcpAbbreviation}:");
+                    Console.Error.Write($"{mcpTimestamp} {mcpAbbreviation}:");
                 }
                 finally
                 {
@@ -153,6 +154,7 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
             }
 
             TextWriter writer = logLevel >= LogLevel.Error ? Console.Error : Console.Out;
+            string timestamp = DateTime.UtcNow.ToString("yyyy-MM-dd'T'HH:mm:ss.fff'Z'");
             // try/finally guarantees the original colors are restored even if Write throws,
             // otherwise the console would be left tinted (e.g. red on error) for subsequent output.
             ConsoleColor originalForeGroundColor = Console.ForegroundColor;
@@ -161,7 +163,7 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
             {
                 Console.ForegroundColor = _logLevelToForeGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.White);
                 Console.BackgroundColor = _logLevelToBackGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.Black);
-                writer.Write($"{abbreviation}:");
+                writer.Write($"{timestamp} {abbreviation}:");
             }
             finally
             {

src/Service/Program.cs

@@ -194,6 +194,11 @@ public static IHostBuilder CreateHostBuilder(string[] args, bool runMcpStdio, st
                     else
                     {
                         logging.SetMinimumLevel(LogLevelProvider.CurrentLogLevel);
+                        logging.AddSimpleConsole(options =>
+                        {
+                            options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                            options.UseUtcTimestamp = true;
+                        });
                     }
 
                     // Add filter for dynamic log level changes (e.g., via MCP logging/setLevel)
@@ -464,6 +469,11 @@ public static ILoggerFactory GetLoggerFactoryForLogLevel(
                         // When LogLevel.None, skip the console logger entirely for true silence.
                         if (LogLevelProvider.CurrentLogLevel != LogLevel.None)
                         {
+                            builder.AddSimpleConsole(options =>
+                            {
+                                options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                                options.UseUtcTimestamp = true;
+                            });
                             builder.AddConsole(options =>
                             {
                                 options.LogToStandardErrorThreshold = LogLevel.Trace;
@@ -472,7 +482,11 @@ public static ILoggerFactory GetLoggerFactoryForLogLevel(
                     }
                     else
                     {
-                        builder.AddConsole();
+                        builder.AddSimpleConsole(options =>
+                        {
+                            options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                            options.UseUtcTimestamp = true;
+                        });
                     }
                 });
         }