revert: remove bridge-level ping interception

Pings should go all the way through to the sandbox MCP server
process. If a server can't handle ping, that's important diagnostic
information that shouldn't be masked at the bridge level.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: andyjmorgan

src/DonkeyWork.CodeSandbox.McpServer/Services/StdioBridge.cs

@@ -188,15 +188,6 @@ void Emit(string eventType, string message, Action<McpStartEvent>? configure = n
         // Extract method name for logging
         var method = ExtractMethod(jsonRpcRequest);
 
-        // Handle ping at the bridge level - not all MCP servers respond to ping
-        if (method == "ping")
-        {
-            _logger.LogInformation("Handling ping request id={Id} at bridge level", requestId);
-            lock (_stateLock) _lastRequestAt = DateTime.UtcNow;
-            var rawId = ExtractRawId(jsonRpcRequest);
-            return $"{{\"jsonrpc\":\"2.0\",\"result\":{{}},\"id\":{rawId}}}";
-        }
-
         _logger.LogInformation("Sending request id={Id} method={Method}, registering TCS", requestId, method);
 
         // Register the TCS BEFORE writing to stdin to avoid a race where
@@ -648,12 +639,6 @@ private static bool IsNotification(string json)
         }
     }
 
-    private static string ExtractRawId(string json)
-    {
-        using var doc = JsonDocument.Parse(json);
-        return doc.RootElement.GetProperty("id").GetRawText();
-    }
-
     private static string? ExtractMethod(string json)
     {
         try