refactor: extract timestamp constant and clarify stdio console config

Author: Copilot

src/Cli/CustomLoggerProvider.cs

@@ -25,6 +25,8 @@ public ILogger CreateLogger(string categoryName)
 
     public class CustomConsoleLogger : ILogger
     {
+        private const string UtcTimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z'";
+
         private readonly LogLevel _minimumLogLevel;
 
         // Minimum LogLevel for CLI output.
@@ -124,7 +126,7 @@ 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'");
+                string mcpTimestamp = DateTime.UtcNow.ToString(UtcTimestampFormat);
                 ConsoleColor mcpOriginalForeGroundColor = Console.ForegroundColor;
                 ConsoleColor mcpOriginalBackGroundColor = Console.BackgroundColor;
                 try
@@ -154,7 +156,7 @@ 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'");
+            string timestamp = DateTime.UtcNow.ToString(UtcTimestampFormat);
             // 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;

src/Service/Program.cs

@@ -26,6 +26,7 @@
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.ApplicationInsights;
+using Microsoft.Extensions.Logging.Console;
 using OpenTelemetry.Exporter;
 using OpenTelemetry.Logs;
 using OpenTelemetry.Resources;
@@ -474,7 +475,9 @@ public static ILoggerFactory GetLoggerFactoryForLogLevel(
                                 options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
                                 options.UseUtcTimestamp = true;
                             });
-                            builder.AddConsole(options =>
+                            // Route all levels to stderr to keep stdout clean for MCP JSON-RPC.
+                            // Uses Services.Configure (not AddConsole) so no second provider is registered.
+                            builder.Services.Configure<ConsoleLoggerOptions>(options =>
                             {
                                 options.LogToStandardErrorThreshold = LogLevel.Trace;
                             });