Production hardening: kill switch, circuit breaker, trailing stops, log level, holiday calendar

TASK-04-log-level.md

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+# TASK-04: Add Log Level Filter to BasicLogger
+
+**File:** `src/NT8.Core/Logging/BasicLogger.cs`
+**Priority:** HIGH
+**No dependencies**
+**Estimated time:** 20 min
+
+---
+
+## Background
+
+`BasicLogger` currently writes every log level to console unconditionally. When `EnableVerboseLogging` is false in NT8, you want to suppress `Debug` and `Trace` output.
+
+The current `ILogger` interface (check `src/NT8.Core/Logging/ILogger.cs`) only defines:
+- `LogDebug`, `LogInformation`, `LogWarning`, `LogError`, `LogCritical`
+
+---
+
+## Exact Changes Required
+
+### 1. Add `LogLevel` enum (check if it already exists first — search the project for `LogLevel`)
+
+If it does NOT already exist, add it inside `BasicLogger.cs` or as a separate file in the same folder:
+
+```csharp
+namespace NT8.Core.Logging
+{
+    /// <summary>
+    /// Log severity levels.
+    /// </summary>
+    public enum LogLevel
+    {
+        Debug = 0,
+        Information = 1,
+        Warning = 2,
+        Error = 3,
+        Critical = 4
+    }
+}
+```
+
+### 2. Add `MinimumLevel` property to `BasicLogger`
+
+```csharp
+/// <summary>
+/// Minimum log level to write. Messages below this level are suppressed.
+/// Default is Information.
+/// </summary>
+public LogLevel MinimumLevel { get; set; }
+```
+
+### 3. Update constructor to default to `Information`
+
+```csharp
+public BasicLogger(string categoryName = "")
+{
+    _categoryName = categoryName;
+    MinimumLevel = LogLevel.Information;
+}
+```
+
+### 4. Update `WriteLog()` to skip below minimum
+
+Add a level parameter and check at the start:
+
+```csharp
+private void WriteLog(LogLevel level, string levelLabel, string message, params object[] args)
+{
+    if (level < MinimumLevel)
+        return;
+
+    var timestamp = DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff");
+    var formattedMessage = args.Length > 0 ? String.Format(message, args) : message;
+    var category = !String.IsNullOrEmpty(_categoryName) ? String.Format("[{0}] ", _categoryName) : "";
+    Console.WriteLine(String.Format("{0} [{1}] {2}{3}", timestamp, levelLabel, category, formattedMessage));
+}
+```
+
+### 5. Update each public method to pass its level
+
+```csharp
+public void LogDebug(string message, params object[] args)
+{
+    WriteLog(LogLevel.Debug, "DEBUG", message, args);
+}
+
+public void LogInformation(string message, params object[] args)
+{
+    WriteLog(LogLevel.Information, "INFO", message, args);
+}
+
+public void LogWarning(string message, params object[] args)
+{
+    WriteLog(LogLevel.Warning, "WARN", message, args);
+}
+
+public void LogError(string message, params object[] args)
+{
+    WriteLog(LogLevel.Error, "ERROR", message, args);
+}
+
+public void LogCritical(string message, params object[] args)
+{
+    WriteLog(LogLevel.Critical, "CRITICAL", message, args);
+}
+```
+
+---
+
+## Acceptance Criteria
+
+- [ ] `MinimumLevel = LogLevel.Warning` suppresses `LogDebug` and `LogInformation` calls
+- [ ] `LogWarning`, `LogError`, `LogCritical` still write when `MinimumLevel = LogLevel.Warning`
+- [ ] Default `MinimumLevel` is `Information` (backward compatible)
+- [ ] `verify-build.bat` passes
+- [ ] All existing tests pass (no test should be checking console output for Debug messages)