nt8-sdk/implementation_guide.md

# NT8 Institutional SDK - Implementation Guide

This guide provides the exact content for all files that need to be created during the implementation of the NT8 Institutional SDK Phase 0.

## 1. Configuration Files

### 1.1 .gitignore
Path: `.gitignore`

Content:
```
# Build results
[Dd]ebug/
[Dd]ebugPublic/
[Rr]elease/
[Rr]eleases/
x64/
x86/
[Ww][Ii][Nn]32/
[Aa][Rr][Mm]/
[Aa][Rr][Mm]64/
bld/
[Bb]in/
[Oo]bj/
[Oo]ut/
[Ll]og/
[Ll]ogs/

# Visual Studio / VSCode
.vs/
.vscode/settings.json
.vscode/tasks.json
.vscode/launch.json
.vscode/extensions.json
*.rsuser
*.suo
*.user
*.userosscache
*.sln.docstates

# Test Results
[Tt]est[Rr]esult*/
[Bb]uild[Ll]og.*
*.VisualState.xml
TestResult.xml
nunit-*.xml
*.trx
*.coverage
*.coveragexml
coverage*.json
coverage*.xml
coverage*.info

# NuGet
*.nupkg
*.snupkg
.nuget/
packages/
!packages/build/
*.nuget.props
*.nuget.targets

# .NET Core
project.lock.json
project.fragment.lock.json
artifacts/

# Development containers
.devcontainer/.env

# Local configuration files
appsettings.local.json
appsettings.*.local.json
config/local.json

# Temporary files
*.tmp
*.temp
.tmp/
.temp/

# IDE specific
*.swp
*.swo
*~

# OS specific
.DS_Store
Thumbs.db

# NinjaTrader specific
*.ninjatrader
*.nt8addon

# Custom tools and scripts output
tools/output/
market-data/*.csv
replay-data/
```

### 1.2 Directory.Build.props
Path: `Directory.Build.props`

Content:
```xml
<Project>
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <LangVersion>10.0</LangVersion>
    <Nullable>enable</Nullable>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
    <GenerateDocumentationFile>true</GenerateDocumentationFile>
    <Company>NT8 Institutional</Company>
    <Product>NT8 SDK</Product>
    <Copyright>Copyright © 2025</Copyright>
    <Version>0.1.0</Version>
    <AssemblyVersion>0.1.0.0</AssemblyVersion>
    <FileVersion>0.1.0.0</FileVersion>
    
    <!-- Code Analysis -->
    <EnableNETAnalyzers>true</EnableNETAnalyzers>
    <AnalysisLevel>6.0</AnalysisLevel>
  </PropertyGroup>

  <PropertyGroup Condition="'$(Configuration)' == 'Debug'">
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <DebugType>portable</DebugType>
  </PropertyGroup>

 <PropertyGroup Condition="'$(Configuration)' == 'Release'">
    <DefineConstants>TRACE</DefineConstants>
    <Optimize>true</Optimize>
    <DebugType>pdbonly</DebugType>
  </PropertyGroup>
  
  <ItemGroup>
    <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="6.0.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
  </ItemGroup>
</Project>
```

### 1.3 .editorconfig
Path: `.editorconfig`

Content:
```ini
# EditorConfig is awesome: https://EditorConfig.org

# top-most EditorConfig file
root = true

[*]
indent_style = space
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true

[*.{cs,csx,vb,vbx}]
indent_size = 4
end_of_line = crlf

[*.{json,js,yml,yaml,xml}]
indent_size = 2

[*.md]
trim_trailing_whitespace = false

# C# formatting rules
[*.cs]
# Organize usings
dotnet_sort_system_directives_first = true
dotnet_separate_import_directive_groups = false

# this. preferences
dotnet_style_qualification_for_field = false:suggestion
dotnet_style_qualification_for_property = false:suggestion
dotnet_style_qualification_for_method = false:suggestion
dotnet_style_qualification_for_event = false:suggestion

# Language keywords vs BCL types preferences
dotnet_style_predefined_type_for_locals_parameters_members = true:suggestion
dotnet_style_predefined_type_for_member_access = true:suggestion

# Modifier preferences
dotnet_style_require_accessibility_modifiers = for_non_interface_members:suggestion
dotnet_style_readonly_field = true:suggestion

# Expression-level preferences
dotnet_style_object_initializer = true:suggestion
dotnet_style_collection_initializer = true:suggestion
dotnet_style_explicit_tuple_names = true:suggestion
dotnet_style_null_propagation = true:suggestion
dotnet_style_coalesce_expression = true:suggestion
dotnet_style_prefer_is_null_check_over_reference_equality_method = true:suggestion
dotnet_style_prefer_inferred_tuple_names = true:suggestion
dotnet_style_prefer_inferred_anonymous_type_member_names = true:suggestion

# C# preferences
csharp_prefer_var_for_built_in_types = false:suggestion
csharp_prefer_var_when_type_is_apparent = true:suggestion
csharp_prefer_var_elsewhere = false:suggestion
```

### 1.4 .gitea/workflows/build.yml
Path: `.gitea/workflows/build.yml`

Content:
```yaml
name: Build and Test

on:
  push:
    branches: [ main, develop ]
  pull_request:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest
    
    steps:
    - uses: actions/checkout@v3
    
    - name: Setup .NET
      uses: actions/setup-dotnet@v3
      with:
        dotnet-version: '6.0.x'
        
    - name: Restore dependencies
      run: dotnet restore
      
    - name: Build
      run: dotnet build --no-restore --configuration Release
      
    - name: Test
      run: dotnet test --no-build --configuration Release --verbosity normal --collect:"XPlat Code Coverage"
      
    - name: Upload coverage reports
      uses: codecov/codecov-action@v3
      with:
        files: ./coverage.cobertura.xml
```

### 1.5 README.md
Path: `README.md`

Content:
```markdown
# NT8 Institutional SDK

Professional-grade algorithmic trading SDK for NinjaTrader 8, built for institutional use with comprehensive risk management and deterministic execution.

## 🚀 Quick Start

### Prerequisites
- .NET 6.0 SDK
- Visual Studio Code + Docker Desktop (recommended)
- Git

### Setup (5 minutes)
```bash
# Clone repository
git clone <repository-url>
cd nt8-institutional-sdk

# Verify setup
dotnet build && dotnet test
```

## 📋 Project Structure

```
src/
├── NT8.Core/           # Core SDK functionality
│   ├── Risk/           # Risk management system
│   ├── Sizing/         # Position sizing algorithms  
│   ├── Logging/        # Structured logging
│   └── Common/         # Shared interfaces and models
├── NT8.Strategies/     # Strategy implementations
├── NT8.Adapters/       # NinjaTrader integration
└── NT8.Contracts/      # API contracts

tests/                  # Comprehensive test suite
tools/                  # Development and deployment tools
docs/                   # Technical documentation
```

## 🏗️ Architecture Principles

- **Risk First**: All trades pass through risk management before execution
- **Deterministic**: Identical inputs produce identical outputs for testing
- **Modular**: Strategies are thin plugins, SDK handles infrastructure
- **Observable**: Structured logging with correlation IDs throughout

## 📊 Current Status: Phase 0 Development

### ✅ Completed
- Development environment and tooling
- Core interfaces and models
- Basic project structure

### 🚧 In Progress
- Risk management implementation
- Position sizing algorithms
- Basic strategy framework
- Comprehensive unit testing

### 📅 Next (Phase 1)
- Order management system
- NinjaTrader integration
- Market data handling
- Advanced testing and validation

## 📄 License

Proprietary - Internal use only
```

## 2. Core SDK Files

### 2.1 IStrategy.cs
Path: `src/NT8.Core/Common/Interfaces/IStrategy.cs`

Content:
```csharp
using NT8.Core.Common.Models;

namespace NT8.Core.Common.Interfaces;

/// <summary>
/// Core strategy interface - strategies implement signal generation only
/// The SDK handles all risk management, position sizing, and order execution
/// </summary>
public interface IStrategy
{
    /// <summary>
    /// Strategy metadata and configuration
    /// </summary>
    StrategyMetadata Metadata { get; }
    
    /// <summary>
    /// Initialize strategy with configuration and dependencies
    /// </summary>
    void Initialize(StrategyConfig config, IMarketDataProvider dataProvider, ILogger logger);
    
    /// <summary>
    /// Process new bar data and generate trading intent (if any)
    /// This is the main entry point for strategy logic
    /// </summary>
    StrategyIntent? OnBar(BarData bar, StrategyContext context);
    
    /// <summary>
    /// Process tick data for high-frequency strategies (optional)
    /// Most strategies can leave this as default implementation
    /// </summary>
    StrategyIntent? OnTick(TickData tick, StrategyContext context) => null;
    
    /// <summary>
    /// Get current strategy parameters for serialization
    /// </summary>
    Dictionary<string, object> GetParameters();
    
    /// <summary>
    /// Update strategy parameters from configuration
    /// </summary>
    void SetParameters(Dictionary<string, object> parameters);
}
```

### 2.2 StrategyMetadata.cs
Path: `src/NT8.Core/Common/Models/StrategyMetadata.cs`

Content:
```csharp
namespace NT8.Core.Common.Models;

/// <summary>
/// Strategy metadata - describes strategy capabilities and requirements
/// </summary>
public record StrategyMetadata(
    string Name,
    string Description,
    string Version,
    string Author,
    string[] Symbols,
    int RequiredBars
);

/// <summary>
/// Strategy configuration passed during initialization
/// </summary>
public record StrategyConfig(
    string Name,
    string Symbol,
    Dictionary<string, object> Parameters,
    RiskConfig RiskSettings,
    SizingConfig SizingSettings
);
```

### 2.3 StrategyIntent.cs
Path: `src/NT8.Core/Common/Models/StrategyIntent.cs`

Content:
```csharp
namespace NT8.Core.Common.Models;

/// <summary>
/// Strategy trading intent - what the strategy wants to do
/// This is the output of strategy logic, input to risk management
/// </summary>
public record StrategyIntent(
    string Symbol,
    OrderSide Side,
    OrderType EntryType,
    double? LimitPrice,
    int StopTicks,
    int? TargetTicks,
    double Confidence,      // 0.0 to 1.0 - strategy confidence level
    string Reason,          // Human-readable reason for trade
    Dictionary<string, object> Metadata  // Additional strategy-specific data
)
{
    /// <summary>
    /// Unique identifier for this intent
    /// </summary>
    public string IntentId { get; init; } = Guid.NewGuid().ToString();
    
    /// <summary>
    /// Timestamp when intent was generated
    /// </summary>
    public DateTime Timestamp { get; init; } = DateTime.UtcNow;
    
    /// <summary>
    /// Validate intent has required fields
    /// </summary>
    public bool IsValid() => 
        !string.IsNullOrEmpty(Symbol) && 
        StopTicks > 0 && 
        Confidence is >= 0.0 and <= 1.0 &&
        Side != OrderSide.Flat &&
        !string.IsNullOrEmpty(Reason);
}

/// <summary>
/// Order side enumeration
/// </summary>
public enum OrderSide
{
    Buy = 1,
    Sell = -1,
    Flat = 0  // Close position
}

/// <summary>
/// Order type enumeration
/// </summary>
public enum OrderType
{
    Market,
    Limit,
    StopMarket,
    StopLimit
}
```

### 2.4 StrategyContext.cs
Path: `src/NT8.Core/Common/Models/StrategyContext.cs`

Content:
```csharp
namespace NT8.Core.Common.Models;

/// <summary>
/// Context information available to strategies
/// </summary>
public record StrategyContext(
    string Symbol,
    DateTime CurrentTime,
    Position CurrentPosition,
    AccountInfo Account,
    MarketSession Session,
    Dictionary<string, object> CustomData
);

/// <summary>
/// Current position information
/// </summary>
public record Position(
    string Symbol,
    int Quantity,
    double AveragePrice,
    double UnrealizedPnL,
    double RealizedPnL,
    DateTime LastUpdate
);

/// <summary>
/// Account information
/// </summary>
public record AccountInfo(
    double Equity,
    double BuyingPower,
    double DailyPnL,
    double MaxDrawdown,
    DateTime LastUpdate
);

/// <summary>
/// Market session information
/// </summary>
public record MarketSession(
    DateTime SessionStart,
    DateTime SessionEnd,
    bool IsRth, // Regular Trading Hours
    string SessionName
);
```

### 2.5 MarketData.cs
Path: `src/NT8.Core/Common/Models/MarketData.cs`

Content:
```csharp
namespace NT8.Core.Common.Models;

/// <summary>
/// Bar data model
/// </summary>
public record BarData(
    string Symbol,
    DateTime Time,
    double Open,
    double High,
    double Low,
    double Close,
    long Volume,
    TimeSpan BarSize
);

/// <summary>
/// Tick data model  
/// </summary>
public record TickData(
    string Symbol,
    DateTime Time,
    double Price,
    int Size,
    TickType Type
);

/// <summary>
/// Order fill model
/// </summary>
public record OrderFill(
    string OrderId,
    string Symbol,
    int Quantity,
    double FillPrice,
    DateTime FillTime,
    double Commission,
    string ExecutionId
);

public enum TickType
{
    Trade,
    Bid,
    Ask,
    Last
}

/// <summary>
/// Market data provider interface
/// </summary>
public interface IMarketDataProvider
{
    /// <summary>
    /// Subscribe to bar data
    /// </summary>
    void SubscribeBars(string symbol, TimeSpan barSize, Action<BarData> onBar);
    
    /// <summary>
    /// Subscribe to tick data
    /// </summary>
    void SubscribeTicks(string symbol, Action<TickData> onTick);
    
    /// <summary>
    /// Get historical bars
    /// </summary>
    Task<List<BarData>> GetHistoricalBars(string symbol, TimeSpan barSize, int count);
    
    /// <summary>
    /// Get current market price
    /// </summary>
    double? GetCurrentPrice(string symbol);
}
```

### 2.6 IRiskManager.cs
Path: `src/NT8.Core/Risk/IRiskManager.cs`

Content:
```csharp
using NT8.Core.Common.Models;

namespace NT8.Core.Risk;

/// <summary>
/// Risk management interface - validates and potentially modifies trading intents
/// This is the gatekeeper between strategy signals and order execution
/// </summary>
public interface IRiskManager
{
    /// <summary>
    /// Validate order intent against risk parameters
    /// Returns decision with allow/reject and any modifications
    /// </summary>
    RiskDecision ValidateOrder(StrategyIntent intent, StrategyContext context, RiskConfig config);
    
    /// <summary>
    /// Update risk state after order fill
    /// </summary>
    void OnFill(OrderFill fill);
    
    /// <summary>
    /// Update risk state with current P&L
    /// </summary>
    void OnPnLUpdate(double netPnL, double dayPnL);
    
    /// <summary>
    /// Emergency flatten all positions
    /// </summary>
    Task<bool> EmergencyFlatten(string reason);
    
    /// <summary>
    /// Get current risk status for monitoring
    /// </summary>
    RiskStatus GetRiskStatus();
}

/// <summary>
/// Risk validation result
/// </summary>
public record RiskDecision(
    bool Allow,
    string? RejectReason,
    StrategyIntent? ModifiedIntent,  // If risk manager modifies size/price
    RiskLevel RiskLevel,
    Dictionary<string, object> RiskMetrics
);

/// <summary>
/// Current risk system status
/// </summary>
public record RiskStatus(
    bool TradingEnabled,
    double DailyPnL,
    double DailyLossLimit,
    double MaxDrawdown,
    int OpenPositions,
    DateTime LastUpdate,
    List<string> ActiveAlerts
);

/// <summary>
/// Risk level classification
/// </summary>
public enum RiskLevel
{
    Low,      // Normal trading
    Medium,   // Elevated caution
    High,     // Limited trading
    Critical  // Trading halted
}

/// <summary>
/// Risk configuration parameters
/// </summary>
public record RiskConfig(
    double DailyLossLimit,
    double MaxTradeRisk,
    int MaxOpenPositions,
    bool EmergencyFlattenEnabled
);
```

### 2.7 BasicRiskManager.cs
Path: `src/NT8.Core/Risk/BasicRiskManager.cs`

Content:
```csharp
using NT8.Core.Common.Models;
using Microsoft.Extensions.Logging;

namespace NT8.Core.Risk;

/// <summary>
/// Basic risk manager implementing Tier 1 risk controls
/// Thread-safe implementation using locks for state consistency
/// </summary>
public class BasicRiskManager : IRiskManager
{
    private readonly ILogger<BasicRiskManager> _logger;
    private readonly object _lock = new();
    
    // Risk state - protected by _lock
    private double _dailyPnL;
    private double _maxDrawdown;
    private bool _tradingHalted;
    private DateTime _lastUpdate = DateTime.UtcNow;
    private readonly Dictionary<string, double> _symbolExposure = new();
    
    public BasicRiskManager(ILogger<BasicRiskManager> logger)
    {
        _logger = logger;
    }
    
    public RiskDecision ValidateOrder(StrategyIntent intent, StrategyContext context, RiskConfig config)
    {
        if (intent == null) throw new ArgumentNullException(nameof(intent));
        if (context == null) throw new ArgumentNullException(nameof(context));
        if (config == null) throw new ArgumentNullException(nameof(config));

        lock (_lock)
        {
            // Check if trading is halted
            if (_tradingHalted)
            {
                _logger.LogWarning("Order rejected - trading halted by risk manager");
                return new RiskDecision(
                    Allow: false,
                    RejectReason: "Trading halted by risk manager",
                    ModifiedIntent: null,
                    RiskLevel: RiskLevel.Critical,
                    RiskMetrics: new() { ["halted"] = true, ["daily_pnl"] = _dailyPnL }
                );
            }
            
            // Tier 1: Daily loss cap
            if (_dailyPnL <= -config.DailyLossLimit)
            {
                _tradingHalted = true;
                _logger.LogCritical("Daily loss limit breached: {DailyPnL:C} <= {Limit:C}", 
                    _dailyPnL, -config.DailyLossLimit);
                
                return new RiskDecision(
                    Allow: false,
                    RejectReason: $"Daily loss limit breached: {_dailyPnL:C}",
                    ModifiedIntent: null,
                    RiskLevel: RiskLevel.Critical,
                    RiskMetrics: new() { ["daily_pnl"] = _dailyPnL, ["limit"] = config.DailyLossLimit }
                );
            }
            
            // Tier 1: Per-trade risk limit
            var tradeRisk = CalculateTradeRisk(intent, context);
            if (tradeRisk > config.MaxTradeRisk)
            {
                _logger.LogWarning("Trade risk too high: {Risk:C} > {Limit:C}", tradeRisk, config.MaxTradeRisk);
                
                return new RiskDecision(
                    Allow: false,
                    RejectReason: $"Trade risk too high: {tradeRisk:C}",
                    ModifiedIntent: null,
                    RiskLevel: RiskLevel.High,
                    RiskMetrics: new() { ["trade_risk"] = tradeRisk, ["limit"] = config.MaxTradeRisk }
                );
            }

            // Tier 1: Position limits
            var currentPositions = GetOpenPositionCount();
            if (currentPositions >= config.MaxOpenPositions && context.CurrentPosition.Quantity == 0)
            {
                _logger.LogWarning("Max open positions exceeded: {Current} >= {Limit}", 
                    currentPositions, config.MaxOpenPositions);
                
                return new RiskDecision(
                    Allow: false,
                    RejectReason: $"Max open positions exceeded: {currentPositions}",
                    ModifiedIntent: null,
                    RiskLevel: RiskLevel.Medium,
                    RiskMetrics: new() { ["open_positions"] = currentPositions, ["limit"] = config.MaxOpenPositions }
                );
            }
            
            // All checks passed - determine risk level
            var riskLevel = DetermineRiskLevel(config);
            
            _logger.LogDebug("Order approved: {Symbol} {Side} risk=${Risk:F2} level={Level}", 
                intent.Symbol, intent.Side, tradeRisk, riskLevel);
            
            return new RiskDecision(
                Allow: true,
                RejectReason: null,
                ModifiedIntent: null,
                RiskLevel: riskLevel,
                RiskMetrics: new() { 
                    ["trade_risk"] = tradeRisk,
                    ["daily_pnl"] = _dailyPnL,
                    ["max_drawdown"] = _maxDrawdown,
                    ["open_positions"] = currentPositions
                }
            );
        }
    }
    
    private static double CalculateTradeRisk(StrategyIntent intent, StrategyContext context)
    {
        // Get tick value for symbol - this will be enhanced in later phases
        var tickValue = GetTickValue(intent.Symbol);
        return intent.StopTicks * tickValue;
    }
    
    private static double GetTickValue(string symbol)
    {
        // Static tick values for Phase 0 - will be configurable in Phase 1
        return symbol switch
        {
            "ES" => 12.50,
            "MES" => 1.25,
            "NQ" => 5.00,
            "MNQ" => 0.50,
            "CL" => 10.00,
            "GC" => 10.00,
            _ => 12.50  // Default to ES
        };
    }
    
    private int GetOpenPositionCount()
    {
        // For Phase 0, return simplified count
        // Will be enhanced with actual position tracking in Phase 1
        return _symbolExposure.Count(kvp => Math.Abs(kvp.Value) > 0.01);
    }
    
    private RiskLevel DetermineRiskLevel(RiskConfig config)
    {
        var lossPercent = Math.Abs(_dailyPnL) / config.DailyLossLimit;
        
        return lossPercent switch
        {
            >= 0.8 => RiskLevel.High,
            >= 0.5 => RiskLevel.Medium,
            _ => RiskLevel.Low
        };
    }
    
    public void OnFill(OrderFill fill)
    {
        if (fill == null) throw new ArgumentNullException(nameof(fill));
        
        lock (_lock)
        {
            _lastUpdate = DateTime.UtcNow;
            
            // Update symbol exposure
            var fillValue = fill.Quantity * fill.FillPrice;
            if (_symbolExposure.ContainsKey(fill.Symbol))
            {
                _symbolExposure[fill.Symbol] += fillValue;
            }
            else
            {
                _symbolExposure[fill.Symbol] = fillValue;
            }
            
            _logger.LogDebug("Fill processed: {Symbol} {Qty} @ {Price:F2}, Exposure: {Exposure:C}", 
                fill.Symbol, fill.Quantity, fill.FillPrice, _symbolExposure[fill.Symbol]);
        }
    }
    
    public void OnPnLUpdate(double netPnL, double dayPnL)
    {
        lock (_lock)
        {
            var oldDailyPnL = _dailyPnL;
            _dailyPnL = dayPnL;
            _maxDrawdown = Math.Min(_maxDrawdown, dayPnL);
            _lastUpdate = DateTime.UtcNow;
            
            if (Math.Abs(dayPnL - oldDailyPnL) > 0.01)
            {
                _logger.LogDebug("P&L Update: Daily={DayPnL:C}, Max DD={MaxDD:C}", 
                    dayPnL, _maxDrawdown);
            }

            // Check for emergency conditions
            CheckEmergencyConditions(dayPnL);
        }
    }
    
    private void CheckEmergencyConditions(double dayPnL)
    {
        // Emergency halt if daily loss exceeds 90% of limit
        if (dayPnL <= -(_dailyPnL * 0.9) && !_tradingHalted)
        {
            _tradingHalted = true;
            _logger.LogCritical("Emergency halt triggered at 90% of daily loss limit: {DayPnL:C}", dayPnL);
        }
    }
    
    public async Task<bool> EmergencyFlatten(string reason)
    {
        if (string.IsNullOrEmpty(reason)) throw new ArgumentException("Reason required", nameof(reason));
        
        lock (_lock)
        {
            _tradingHalted = true;
            _logger.LogCritical("Emergency flatten triggered: {Reason}", reason);
        }
        
        // In Phase 0, this is a placeholder
        // Phase 1 will implement actual position flattening via OMS
        await Task.Delay(100);
        
        _logger.LogInformation("Emergency flatten completed");
        return true;
    }
    
    public RiskStatus GetRiskStatus()
    {
        lock (_lock)
        {
            var alerts = new List<string>();
            
            if (_tradingHalted)
                alerts.Add("Trading halted");
            
            if (_dailyPnL <= -500) // Half of typical daily limit
                alerts.Add($"Significant daily loss: {_dailyPnL:C}");
            
            if (_maxDrawdown <= -1000)
                alerts.Add($"Large drawdown: {_maxDrawdown:C}");
            
            return new RiskStatus(
                TradingEnabled: !_tradingHalted,
                DailyPnL: _dailyPnL,
                DailyLossLimit: 1000, // Will come from config in Phase 1
                MaxDrawdown: _maxDrawdown,
                OpenPositions: GetOpenPositionCount(),
                LastUpdate: _lastUpdate,
                ActiveAlerts: alerts
            );
        }
    }
    
    /// <summary>
    /// Reset daily state - typically called at start of new trading day
    /// </summary>
    public void ResetDaily()
    {
        lock (_lock)
        {
            _dailyPnL = 0;
            _maxDrawdown = 0;
            _tradingHalted = false;
            _symbolExposure.Clear();
            _lastUpdate = DateTime.UtcNow;
            
            _logger.LogInformation("Daily risk state reset");
        }
    }
}
```

### 2.8 IPositionSizer.cs
Path: `src/NT8.Core/Sizing/IPositionSizer.cs`

Content:
```csharp
using NT8.Core.Common.Models;

namespace NT8.Core.Sizing;

/// <summary>
/// Position sizing interface - determines contract quantity
/// </summary>
public interface IPositionSizer
{
    /// <summary>
    /// Calculate position size for trading intent
    /// </summary>
    SizingResult CalculateSize(StrategyIntent intent, StrategyContext context, SizingConfig config);
    
    /// <summary>
    /// Get sizing component metadata
    /// </summary>
    SizingMetadata GetMetadata();
}

/// <summary>
/// Position sizing result
/// </summary>
public record SizingResult(
    int Contracts,
    double RiskAmount,
    SizingMethod Method,
    Dictionary<string, object> Calculations
);

/// <summary>
/// Sizing component metadata
/// </summary>
public record SizingMetadata(
    string Name,
    string Description,
    List<string> RequiredParameters
);

/// <summary>
/// Position sizing configuration
/// </summary>
public record SizingConfig(
    SizingMethod Method,
    int MinContracts,
    int MaxContracts,
    double RiskPerTrade,
    Dictionary<string, object> MethodParameters
);

/// <summary>
/// Position sizing methods
/// </summary>
public enum SizingMethod
{
    FixedContracts,
    FixedDollarRisk,
    OptimalF,        // Will be implemented in Phase 1
    KellyCriterion   // Will be implemented in Phase 1
}
```

### 2.9 BasicPositionSizer.cs
Path: `src/NT8.Core/Sizing/BasicPositionSizer.cs`

Content:
```csharp
using NT8.Core.Common.Models;
using Microsoft.Extensions.Logging;

namespace NT8.Core.Sizing;

/// <summary>
/// Basic position sizer with fixed contracts and fixed dollar risk methods
/// Handles contract size calculations with proper rounding and clamping
/// </summary>
public class BasicPositionSizer : IPositionSizer
{
    private readonly ILogger<BasicPositionSizer> _logger;
    
    public BasicPositionSizer(ILogger<BasicPositionSizer> logger)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }
    
    public SizingResult CalculateSize(StrategyIntent intent, StrategyContext context, SizingConfig config)
    {
        if (intent == null) throw new ArgumentNullException(nameof(intent));
        if (context == null) throw new ArgumentNullException(nameof(context));
        if (config == null) throw new ArgumentNullException(nameof(config));

        // Validate intent is suitable for sizing
        if (!intent.IsValid())
        {
            _logger.LogWarning("Invalid strategy intent provided for sizing: {Intent}", intent);
            return new SizingResult(0, 0, config.Method, new() { ["error"] = "Invalid intent" });
        }

        return config.Method switch
        {
            SizingMethod.FixedContracts => CalculateFixedContracts(intent, context, config),
            SizingMethod.FixedDollarRisk => CalculateFixedRisk(intent, context, config),
            _ => throw new NotSupportedException($"Sizing method {config.Method} not supported in Phase 0")
        };
    }
    
    private SizingResult CalculateFixedContracts(StrategyIntent intent, StrategyContext context, SizingConfig config)
    {
        // Get target contracts from configuration
        var targetContracts = GetParameterValue<int>(config, "contracts", 1);
        
        // Apply min/max clamping
        var contracts = Math.Max(config.MinContracts, 
                        Math.Min(config.MaxContracts, targetContracts));
        
        // Calculate actual risk amount
        var tickValue = GetTickValue(intent.Symbol);
        var riskAmount = contracts * intent.StopTicks * tickValue;
        
        _logger.LogDebug("Fixed contracts sizing: {Symbol} {TargetContracts}→{ActualContracts} contracts, ${Risk:F2} risk", 
            intent.Symbol, targetContracts, contracts, riskAmount);
        
        return new SizingResult(
            Contracts: contracts,
            RiskAmount: riskAmount,
            Method: SizingMethod.FixedContracts,
            Calculations: new()
            {
                ["target_contracts"] = targetContracts,
                ["clamped_contracts"] = contracts,
                ["stop_ticks"] = intent.StopTicks,
                ["tick_value"] = tickValue,
                ["risk_amount"] = riskAmount,
                ["min_contracts"] = config.MinContracts,
                ["max_contracts"] = config.MaxContracts
            }
        );
    }
    
    private SizingResult CalculateFixedRisk(StrategyIntent intent, StrategyContext context, SizingConfig config)
    {
        var tickValue = GetTickValue(intent.Symbol);
        
        // Validate stop ticks
        if (intent.StopTicks <= 0)
        {
            _logger.LogWarning("Invalid stop ticks {StopTicks} for fixed risk sizing on {Symbol}", 
                intent.StopTicks, intent.Symbol);
            
            return new SizingResult(0, 0, SizingMethod.FixedDollarRisk, 
                new() { ["error"] = "Invalid stop ticks", ["stop_ticks"] = intent.StopTicks });
        }
        
        // Calculate optimal contracts for target risk
        var targetRisk = config.RiskPerTrade;
        var riskPerContract = intent.StopTicks * tickValue;
        var optimalContracts = targetRisk / riskPerContract;
        
        // Round down to whole contracts (conservative approach)
        var contracts = (int)Math.Floor(optimalContracts);
        
        // Apply min/max clamping
        contracts = Math.Max(config.MinContracts, Math.Min(config.MaxContracts, contracts));
        
        // Calculate actual risk with final contract count
        var actualRisk = contracts * riskPerContract;
        
        _logger.LogDebug("Fixed risk sizing: {Symbol} ${TargetRisk:F2}→{OptimalContracts:F2}→{ActualContracts} contracts, ${ActualRisk:F2} actual risk", 
            intent.Symbol, targetRisk, optimalContracts, contracts, actualRisk);
        
        return new SizingResult(
            Contracts: contracts,
            RiskAmount: actualRisk,
            Method: SizingMethod.FixedDollarRisk,
            Calculations: new()
            {
                ["target_risk"] = targetRisk,
                ["stop_ticks"] = intent.StopTicks,
                ["tick_value"] = tickValue,
                ["risk_per_contract"] = riskPerContract,
                ["optimal_contracts"] = optimalContracts,
                ["clamped_contracts"] = contracts,
                ["actual_risk"] = actualRisk,
                ["min_contracts"] = config.MinContracts,
                ["max_contracts"] = config.MaxContracts
            }
        );
    }
    
    private static T GetParameterValue<T>(SizingConfig config, string key, T defaultValue)
    {
        if (config.MethodParameters.TryGetValue(key, out var value))
        {
            try
            {
                return (T)Convert.ChangeType(value, typeof(T));
            }
            catch
            {
                // If conversion fails, return default
                return defaultValue;
            }
        }
        
        return defaultValue;
    }
    
    private static double GetTickValue(string symbol)
    {
        // Static tick values for Phase 0 - will be configurable in Phase 1
        return symbol switch
        {
            "ES" => 12.50,   // E-mini S&P 500
            "MES" => 1.25,   // Micro E-mini S&P 500
            "NQ" => 5.00,    // E-mini NASDAQ-100
            "MNQ" => 0.50,   // Micro E-mini NASDAQ-100
            "CL" => 10.00,   // Crude Oil
            "GC" => 10.00,   // Gold
            "6E" => 12.50,   // Euro FX
            "6A" => 10.00,   // Australian Dollar
            _ => 12.50       // Default to ES value
        };
    }
    
    public SizingMetadata GetMetadata()
    {
        return new SizingMetadata(
            Name: "Basic Position Sizer",
            Description: "Fixed contracts or fixed dollar risk sizing with contract clamping",
            RequiredParameters: new List<string> { "method", "risk_per_trade", "min_contracts", "max_contracts" }
        );
    }
    
    /// <summary>
    /// Validate sizing configuration parameters
    /// </summary>
    public static bool ValidateConfig(SizingConfig config, out List<string> errors)
    {
        errors = new List<string>();
        
        if (config.MinContracts < 0)
            errors.Add("MinContracts must be >= 0");
            
        if (config.MaxContracts <= 0)
            errors.Add("MaxContracts must be > 0");
            
        if (config.MinContracts > config.MaxContracts)
            errors.Add("MinContracts must be <= MaxContracts");
            
        if (config.RiskPerTrade <= 0)
            errors.Add("RiskPerTrade must be > 0");
            
        // Method-specific validation
        switch (config.Method)
        {
            case SizingMethod.FixedContracts:
                if (!config.MethodParameters.ContainsKey("contracts"))
                    errors.Add("FixedContracts method requires 'contracts' parameter");
                else if (GetParameterValue<int>(config, "contracts", 0) <= 0)
                    errors.Add("Fixed contracts parameter must be > 0");
                break;
                
            case SizingMethod.FixedDollarRisk:
                // No additional parameters required for fixed dollar risk
                break;
                
            default:
                errors.Add($"Unsupported sizing method: {config.Method}");
                break;
        }
        
        return errors.Count == 0;
    }
    
    /// <summary>
    /// Get supported symbols with their tick values
    /// </summary>
    public static Dictionary<string, double> GetSupportedSymbols()
    {
        return new Dictionary<string, double>
        {
            ["ES"] = 12.50,
            ["MES"] = 1.25,
            ["NQ"] = 5.00,
            ["MNQ"] = 0.50,
            ["CL"] = 10.00,
            ["GC"] = 10.00,
            ["6E"] = 12.50,
            ["6A"] = 10.00
        };
    }
}
```

## 3. Test Files

### 3.1 BasicRiskManagerTests.cs
Path: `tests/NT8.Core.Tests/Risk/BasicRiskManagerTests.cs`

Content:
```csharp
using NT8.Core.Risk;
using NT8.Core.Common.Models;
using NT8.Core.Tests.TestHelpers;
using Microsoft.Extensions.Logging;
using FluentAssertions;
using Xunit;
using Microsoft.Extensions.Logging.Abstractions;

namespace NT8.Core.Tests.Risk;

public class BasicRiskManagerTests : IDisposable
{
    private readonly ILogger<BasicRiskManager> _logger;
    private readonly BasicRiskManager _riskManager;
    
    public BasicRiskManagerTests()
    {
        _logger = NullLogger<BasicRiskManager>.Instance;
        _riskManager = new BasicRiskManager(_logger);
    }
    
    [Fact]
    public void ValidateOrder_WithinLimits_ShouldAllow()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(stopTicks: 8);
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestRiskConfig();
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeTrue();
        result.RejectReason.Should().BeNull();
        result.RiskLevel.Should().Be(RiskLevel.Low);
        result.RiskMetrics.Should().ContainKey("trade_risk");
        result.RiskMetrics.Should().ContainKey("daily_pnl");
    }
    
    [Fact]
    public void ValidateOrder_ExceedsDailyLimit_ShouldReject()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = new RiskConfig(
            DailyLossLimit: 1000,
            MaxTradeRisk: 500,
            MaxOpenPositions: 5,
            EmergencyFlattenEnabled: true
        );
        
        // Simulate daily loss exceeding limit
        _riskManager.OnPnLUpdate(0, -1001);
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Daily loss limit breached");
        result.RiskLevel.Should().Be(RiskLevel.Critical);
        result.RiskMetrics["daily_pnl"].Should().Be(-1001);
    }
    
    [Fact]
    public void ValidateOrder_ExceedsTradeRisk_ShouldReject()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(stopTicks: 100); // High risk trade
        var context = TestDataBuilder.CreateTestContext();
        var config = new RiskConfig(
            DailyLossLimit: 10000,
            MaxTradeRisk: 500, // Lower than calculated trade risk
            MaxOpenPositions: 5,
            EmergencyFlattenEnabled: true
        );
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Trade risk too high");
        result.RiskLevel.Should().Be(RiskLevel.High);
        
        // Verify risk calculation
        var expectedRisk = 100 * 12.50; // 100 ticks * ES tick value
        result.RiskMetrics["trade_risk"].Should().Be(expectedRisk);
    }
    
    [Theory]
    [InlineData("ES", 8, 100.0)]   // ES: 8 ticks * $12.50 = $100
    [InlineData("MES", 8, 10.0)]   // MES: 8 ticks * $1.25 = $10
    [InlineData("NQ", 4, 20.0)]    // NQ: 4 ticks * $5.00 = $20
    [InlineData("MNQ", 10, 5.0)]   // MNQ: 10 ticks * $0.50 = $5
    public void ValidateOrder_RiskCalculation_ShouldBeAccurate(string symbol, int stopTicks, double expectedRisk)
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: symbol, stopTicks: stopTicks);
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestRiskConfig();
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeTrue();
        result.RiskMetrics["trade_risk"].Should().Be(expectedRisk);
    }
    
    [Fact]
    public void ValidateOrder_MaxPositionsExceeded_ShouldReject()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = new RiskConfig(
            DailyLossLimit: 10000,
            MaxTradeRisk: 1000,
            MaxOpenPositions: 1, // Very low limit
            EmergencyFlattenEnabled: true
        );
        
        // Simulate existing position by processing a fill
        var fill = new OrderFill(
            OrderId: Guid.NewGuid().ToString(),
            Symbol: "NQ",
            Quantity: 2,
            FillPrice: 15000.0,
            FillTime: DateTime.UtcNow,
            Commission: 5.0,
            ExecutionId: Guid.NewGuid().ToString()
        );
        _riskManager.OnFill(fill);
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Max open positions exceeded");
        result.RiskLevel.Should().Be(RiskLevel.Medium);
    }
    
    [Fact]
    public async Task EmergencyFlatten_ShouldHaltTrading()
    {
        // Arrange
        var reason = "Test emergency halt";
        
        // Act
        var result = await _riskManager.EmergencyFlatten(reason);
        var status = _riskManager.GetRiskStatus();
        
        // Assert
        result.Should().BeTrue();
        status.TradingEnabled.Should().BeFalse();
        status.ActiveAlerts.Should().Contain("Trading halted");
    }
    
    [Fact]
    public async Task EmergencyFlatten_WithNullReason_ShouldThrow()
    {
        // Act & Assert
        await Assert.ThrowsAsync<ArgumentException>(() => _riskManager.EmergencyFlatten(null));
        await Assert.ThrowsAsync<ArgumentException>(() => _riskManager.EmergencyFlatten(""));
    }
    
    [Fact]
    public void ValidateOrder_AfterEmergencyFlatten_ShouldRejectAllOrders()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestRiskConfig();
        
        // Trigger emergency flatten
        _riskManager.EmergencyFlatten("Test").Wait();
        
        // Act
        var result = _riskManager.ValidateOrder(intent, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Trading halted");
        result.RiskLevel.Should().Be(RiskLevel.Critical);
    }
    
    [Fact]
    public void OnPnLUpdate_WithLargeDrawdown_ShouldUpdateStatus()
    {
        // Arrange
        var largeLoss = -1500.0;
        
        // Act
        _riskManager.OnPnLUpdate(largeLoss, largeLoss);
        var status = _riskManager.GetRiskStatus();
        
        // Assert
        status.DailyPnL.Should().Be(largeLoss);
        status.MaxDrawdown.Should().Be(largeLoss);
        status.ActiveAlerts.Should().Contain(alert => alert.Contains("drawdown"));
    }
    
    [Fact]
    public void OnFill_ShouldUpdateExposure()
    {
        // Arrange
        var fill = new OrderFill(
            OrderId: Guid.NewGuid().ToString(),
            Symbol: "ES",
            Quantity: 2,
            FillPrice: 4200.0,
            FillTime: DateTime.UtcNow,
            Commission: 4.50,
            ExecutionId: Guid.NewGuid().ToString()
        );
        
        // Act
        _riskManager.OnFill(fill);
        var status = _riskManager.GetRiskStatus();
        
        // Assert
        status.LastUpdate.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromSeconds(1));
    }
    
    [Fact]
    public void ValidateOrder_WithNullParameters_ShouldThrow()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestRiskConfig();
        
        // Act & Assert
        Assert.Throws<ArgumentNullException>(() => _riskManager.ValidateOrder(null, context, config));
        Assert.Throws<ArgumentNullException>(() => _riskManager.ValidateOrder(intent, null, config));
        Assert.Throws<ArgumentNullException>(() => _riskManager.ValidateOrder(intent, context, null));
    }
    
    [Fact]
    public void RiskLevel_ShouldEscalateWithLosses()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = new RiskConfig(100, 500, 5, true); // $1000 daily limit
        
        // Act & Assert - Low risk (no losses)
        var result1 = _riskManager.ValidateOrder(intent, context, config);
        result1.RiskLevel.Should().Be(RiskLevel.Low);
        
        // Medium risk (50% of daily limit)
        _riskManager.OnPnLUpdate(-500, -500);
        var result2 = _riskManager.ValidateOrder(intent, context, config);
        result2.RiskLevel.Should().Be(RiskLevel.Medium);
        
        // High risk (80% of daily limit)
        _riskManager.OnPnLUpdate(-800, -800);
        var result3 = _riskManager.ValidateOrder(intent, context, config);
        result3.RiskLevel.Should().Be(RiskLevel.High);
    }
    
    [Fact]
    public void ResetDaily_ShouldClearState()
    {
        // Arrange - Set up some risk state
        _riskManager.OnPnLUpdate(-500, -500);
        var fill = new OrderFill("test", "ES", 2, 4200, DateTime.UtcNow, 4.50, "exec1");
        _riskManager.OnFill(fill);
        
        // Act
        _riskManager.ResetDaily();
        var status = _riskManager.GetRiskStatus();
        
        // Assert
        status.DailyPnL.Should().Be(0);
        status.MaxDrawdown.Should().Be(0);
        status.TradingEnabled.Should().BeTrue();
        status.OpenPositions.Should().Be(0);
        status.ActiveAlerts.Should().BeEmpty();
    }
    
    [Fact]
    public void GetRiskStatus_ShouldReturnCurrentState()
    {
        // Arrange
        var testPnL = -300.0;
        _riskManager.OnPnLUpdate(testPnL, testPnL);
        
        // Act
        var status = _riskManager.GetRiskStatus();
        
        // Assert
        status.TradingEnabled.Should().BeTrue();
        status.DailyPnL.Should().Be(testPnL);
        status.MaxDrawdown.Should().Be(testPnL);
        status.LastUpdate.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromSeconds(1));
        status.ActiveAlerts.Should().NotBeNull();
    }
    
    [Fact]
    public void ConcurrentAccess_ShouldBeThreadSafe()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestRiskConfig();
        var tasks = new List<Task>();
        
        // Act - Multiple threads accessing simultaneously
        for (int i = 0; i < 10; i++)
        {
            tasks.Add(Task.Run(() =>
            {
                _riskManager.ValidateOrder(intent, context, config);
                _riskManager.OnPnLUpdate(-10 * i, -10 * i);
            }));
        }
        
        Task.WaitAll(tasks.ToArray());
        
        // Assert - Should not throw and should have consistent state
        var status = _riskManager.GetRiskStatus();
        status.Should().NotBeNull();
        status.LastUpdate.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromSeconds(1));
    }
    
    public void Dispose()
    {
        // Cleanup if needed
    }
}
```

### 3.2 RiskScenarioTests.cs
Path: `tests/NT8.Core.Tests/Risk/RiskScenarioTests.cs`

Content:
```csharp
using NT8.Core.Risk;
using NT8.Core.Common.Models;
using NT8.Core.Tests.TestHelpers;
using Microsoft.Extensions.Logging.Abstractions;
using FluentAssertions;
using Xunit;

namespace NT8.Core.Tests.Risk;

/// <summary>
/// Comprehensive risk scenario testing
/// These tests validate the risk manager against real-world trading scenarios
/// </summary>
public class RiskScenarioTests
{
    private readonly BasicRiskManager _riskManager;
    
    public RiskScenarioTests()
    {
        _riskManager = new BasicRiskManager(NullLogger<BasicRiskManager>.Instance);
    }
    
    [Fact]
    public void Scenario_TypicalTradingDay_ShouldManageRiskCorrectly()
    {
        // Arrange - Typical day configuration
        var config = new RiskConfig(
            DailyLossLimit: 1000,
            MaxTradeRisk: 200,
            MaxOpenPositions: 3,
            EmergencyFlattenEnabled: true
        );
        
        var context = TestDataBuilder.CreateTestContext();
        
        // Act & Assert - Morning trades should be allowed
        var morningTrade1 = TestDataBuilder.CreateValidIntent(stopTicks: 8); // $10 risk
        var result1 = _riskManager.ValidateOrder(morningTrade1, context, config);
        result1.Allow.Should().BeTrue();
        result1.RiskLevel.Should().Be(RiskLevel.Low);
        
        // Simulate some losses
        _riskManager.OnPnLUpdate(-150, -150);
        
        var morningTrade2 = TestDataBuilder.CreateValidIntent(stopTicks: 12); // $150 risk
        var result2 = _riskManager.ValidateOrder(morningTrade2, context, config);
        result2.Allow.Should().BeTrue();
        result2.RiskLevel.Should().Be(RiskLevel.Low);
        
        // More losses - should escalate risk level
        _riskManager.OnPnLUpdate(-600, -600);
        
        var afternoonTrade = TestDataBuilder.CreateValidIntent(stopTicks: 8);
        var result3 = _riskManager.ValidateOrder(afternoonTrade, context, config);
        result3.Allow.Should().BeTrue();
        result3.RiskLevel.Should().Be(RiskLevel.Medium); // Should escalate
        
        // Near daily limit - high risk
        _riskManager.OnPnLUpdate(-850, -850);
        
        var lateTrade = TestDataBuilder.CreateValidIntent(stopTicks: 8);
        var result4 = _riskManager.ValidateOrder(lateTrade, context, config);
        result4.Allow.Should().BeTrue();
        result4.RiskLevel.Should().Be(RiskLevel.High);
        
        // Exceed daily limit - should halt
        _riskManager.OnPnLUpdate(-1050, -1050);
        
        var deniedTrade = TestDataBuilder.CreateValidIntent(stopTicks: 4);
        var result5 = _riskManager.ValidateOrder(deniedTrade, context, config);
        result5.Allow.Should().BeFalse();
        result5.RiskLevel.Should().Be(RiskLevel.Critical);
    }
    
    [Fact]
    public void Scenario_HighRiskTrade_ShouldBeRejected()
    {
        // Arrange - Conservative risk settings
        var config = new RiskConfig(
            DailyLossLimit: 2000,
            MaxTradeRisk: 10, // Very conservative
            MaxOpenPositions: 5,
            EmergencyFlattenEnabled: true
        );
        
        var context = TestDataBuilder.CreateTestContext();
        
        // Act - Try to place high-risk trade
        var highRiskTrade = TestDataBuilder.CreateValidIntent(
            symbol: "ES",
            stopTicks: 20 // $250 risk, exceeds $100 limit
        );
        
        var result = _riskManager.ValidateOrder(highRiskTrade, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Trade risk too high");
        result.RiskMetrics["trade_risk"].Should().Be(250.0); // 20 * $12.50
        result.RiskMetrics["limit"].Should().Be(100.0);
    }
    
    [Fact]
    public void Scenario_MaxPositions_ShouldLimitNewTrades()
    {
        // Arrange - Low position limit
        var config = new RiskConfig(
            DailyLossLimit: 5000,
            MaxTradeRisk: 500,
            MaxOpenPositions: 2,
            EmergencyFlattenEnabled: true
        );
        
        var context = TestDataBuilder.CreateTestContext();
        
        // Fill up position slots
        var fill1 = new OrderFill("order1", "ES", 1, 4200, DateTime.UtcNow, 2.25, "exec1");
        var fill2 = new OrderFill("order2", "NQ", 1, 15000, DateTime.UtcNow, 2.50, "exec2");
        
        _riskManager.OnFill(fill1);
        _riskManager.OnFill(fill2);
        
        // Act - Try to add another position
        var newTrade = TestDataBuilder.CreateValidIntent(symbol: "CL");
        var result = _riskManager.ValidateOrder(newTrade, context, config);
        
        // Assert
        result.Allow.Should().BeFalse();
        result.RejectReason.Should().Contain("Max open positions exceeded");
        result.RiskLevel.Should().Be(RiskLevel.Medium);
    }
    
    [Fact]
    public void Scenario_RecoveryAfterReset_ShouldAllowTrading()
    {
        // Arrange - Simulate end of bad trading day
        var config = TestDataBuilder.CreateTestRiskConfig();
        var context = TestDataBuilder.CreateTestContext();
        
        // Simulate terrible day with emergency halt
        _riskManager.OnPnLUpdate(-1500, -1500);
        _riskManager.EmergencyFlatten("End of day").Wait();
        
        var haltedTrade = TestDataBuilder.CreateValidIntent();
        var haltedResult = _riskManager.ValidateOrder(haltedTrade, context, config);
        haltedResult.Allow.Should().BeFalse();
        
        // Act - Reset for new day
        _riskManager.ResetDaily();
        
        var newDayTrade = TestDataBuilder.CreateValidIntent();
        var newResult = _riskManager.ValidateOrder(newDayTrade, context, config);
        
        // Assert - Should be back to normal
        newResult.Allow.Should().BeTrue();
        newResult.RiskLevel.Should().Be(RiskLevel.Low);
        
        var status = _riskManager.GetRiskStatus();
        status.TradingEnabled.Should().BeTrue();
        status.DailyPnL.Should().Be(0);
        status.ActiveAlerts.Should().BeEmpty();
    }
    
    [Fact]
    public void Scenario_VolatileMarket_ShouldHandleMultipleSymbols()
    {
        // Arrange - Multi-symbol trading
        var config = new RiskConfig(
            DailyLossLimit: 2000,
            MaxTradeRisk: 300,
            MaxOpenPositions: 4,
            EmergencyFlattenEnabled: true
        );
        
        var context = TestDataBuilder.CreateTestContext();
        
        // Act - Trade multiple symbols
        var esTrade = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 16); // $200 risk
        var nqTrade = TestDataBuilder.CreateValidIntent(symbol: "NQ", stopTicks: 40);  // $200 risk
        var clTrade = TestDataBuilder.CreateValidIntent(symbol: "CL", stopTicks: 20);  // $200 risk
        
        var esResult = _riskManager.ValidateOrder(esTrade, context, config);
        var nqResult = _riskManager.ValidateOrder(nqTrade, context, config);
        var clResult = _riskManager.ValidateOrder(clTrade, context, config);
        
        // Assert - All should be allowed
        esResult.Allow.Should().BeTrue();
        nqResult.Allow.Should().BeTrue();
        clResult.Allow.Should().BeTrue();
        
        // Verify risk calculations are symbol-specific
        esResult.RiskMetrics["trade_risk"].Should().Be(200.0); // ES: 16 * $12.50
        nqResult.RiskMetrics["trade_risk"].Should().Be(200.0); // NQ: 40 * $5.00
        clResult.RiskMetrics["trade_risk"].Should().Be(200.0); // CL: 20 * $10.00
    }
    
    [Fact]
    public void Scenario_GradualLossEscalation_ShouldShowRiskProgression()
    {
        // Arrange
        var config = new RiskConfig(
            DailyLossLimit: 1000,
            MaxTradeRisk: 200,
            MaxOpenPositions: 5,
            EmergencyFlattenEnabled: true
        );
        
        var context = TestDataBuilder.CreateTestContext();
        var intent = TestDataBuilder.CreateValidIntent(stopTicks: 8);
        
        // Act & Assert - Track risk level escalation
        var results = new List<(double loss, RiskLevel level)>();
        
        // Start: No losses
        var result0 = _riskManager.ValidateOrder(intent, context, config);
        results.Add((0, result0.RiskLevel));
        
        // 30% loss
        _riskManager.OnPnLUpdate(-300, -300);
        var result1 = _riskManager.ValidateOrder(intent, context, config);
        results.Add((-300, result1.RiskLevel));
        
        // 50% loss
        _riskManager.OnPnLUpdate(-500, -500);
        var result2 = _riskManager.ValidateOrder(intent, context, config);
        results.Add((-500, result2.RiskLevel));
        
        // 80% loss
        _riskManager.OnPnLUpdate(-800, -800);
        var result3 = _riskManager.ValidateOrder(intent, context, config);
        results.Add((-800, result3.RiskLevel));
        
        // Assert escalation pattern
        results[0].level.Should().Be(RiskLevel.Low);    // 0% loss
        results[1].level.Should().Be(RiskLevel.Low);    // 30% loss
        results[2].level.Should().Be(RiskLevel.Medium); // 50% loss
        results[3].level.Should().Be(RiskLevel.High);   // 80% loss
    }
}
```

### 3.3 BasicPositionSizerTests.cs
Path: `tests/NT8.Core.Tests/Sizing/BasicPositionSizerTests.cs`

Content:
```csharp
using NT8.Core.Sizing;
using NT8.Core.Common.Models;
using NT8.Core.Tests.TestHelpers;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using FluentAssertions;
using Xunit;

namespace NT8.Core.Tests.Sizing;

public class BasicPositionSizerTests : IDisposable
{
    private readonly ILogger<BasicPositionSizer> _logger;
    private readonly BasicPositionSizer _sizer;
    
    public BasicPositionSizerTests()
    {
        _logger = NullLogger<BasicPositionSizer>.Instance;
        _sizer = new BasicPositionSizer(_logger);
    }
    
    [Fact]
    public void CalculateSize_FixedContracts_ShouldReturnCorrectSize()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 8);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedContracts,
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: 200,
            MethodParameters: new() { ["contracts"] = 3 }
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(3);
        result.Method.Should().Be(SizingMethod.FixedContracts);
        result.RiskAmount.Should().Be(300.0); // 3 contracts * 8 ticks * $12.50
        result.Calculations.Should().ContainKey("target_contracts");
        result.Calculations.Should().ContainKey("clamped_contracts");
        result.Calculations["target_contracts"].Should().Be(3);
        result.Calculations["clamped_contracts"].Should().Be(3);
    }
    
    [Fact]
    public void CalculateSize_FixedContractsWithClamping_ShouldApplyLimits()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 10);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedContracts,
            MinContracts: 2,
            MaxContracts: 5,
            RiskPerTrade: 200,
            MethodParameters: new() { ["contracts"] = 8 } // Exceeds max
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(5); // Clamped to max
        result.Calculations["target_contracts"].Should().Be(8);
        result.Calculations["clamped_contracts"].Should().Be(5);
        result.RiskAmount.Should().Be(625.0); // 5 * 10 * $12.50
    }
    
    [Fact]
    public void CalculateSize_FixedDollarRisk_ShouldCalculateCorrectly()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 10);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedDollarRisk,
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: 250.0, // Target $250 risk
            MethodParameters: new()
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        // $250 target / (10 ticks * $12.50) = 2 contracts
        result.Contracts.Should().Be(2);
        result.Method.Should().Be(SizingMethod.FixedDollarRisk);
        result.RiskAmount.Should().Be(250.0); // 2 * 10 * $12.50
        result.Calculations["target_risk"].Should().Be(250.0);
        result.Calculations["optimal_contracts"].Should().Be(2.0);
        result.Calculations["actual_risk"].Should().Be(250.0);
    }
    
    [Theory]
    [InlineData("ES", 8, 200.0, 2, 200.0)]   // ES: $200 / (8 * $12.50) = 2.0 → 2 contracts
    [InlineData("MES", 8, 20.0, 2, 20.0)]    // MES: $20 / (8 * $1.25) = 2.0 → 2 contracts  
    [InlineData("NQ", 10, 100.0, 2, 100.0)]  // NQ: $100 / (10 * $5.00) = 2.0 → 2 contracts
    [InlineData("CL", 5, 75.0, 1, 50.0)]     // CL: $75 / (5 * $10.00) = 1.5 → 1 contract (floor)
    public void CalculateSize_FixedRiskVariousSymbols_ShouldCalculateCorrectly(
        string symbol, int stopTicks, double targetRisk, int expectedContracts, double expectedActualRisk)
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: symbol, stopTicks: stopTicks);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedDollarRisk,
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: targetRisk,
            MethodParameters: new()
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(expectedContracts);
        result.RiskAmount.Should().Be(expectedActualRisk);
        result.Method.Should().Be(SizingMethod.FixedDollarRisk);
    }
    
    [Fact]
    public void CalculateSize_FixedRiskWithMinClamp_ShouldApplyMinimum()
    {
        // Arrange - Very small risk that would calculate to 0 contracts
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 20);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedDollarRisk,
            MinContracts: 2, // Force minimum
            MaxContracts: 10,
            RiskPerTrade: 100.0, // Only enough for 0.4 contracts
            MethodParameters: new()
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(2); // Applied minimum
        result.RiskAmount.Should().Be(500.0); // 2 * 20 * $12.50
        result.Calculations["optimal_contracts"].Should().Be(0.4);
        result.Calculations["clamped_contracts"].Should().Be(2);
    }
    
    [Fact]
    public void CalculateSize_FixedRiskWithMaxClamp_ShouldApplyMaximum()
    {
        // Arrange - Large risk that would calculate to many contracts
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 5);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedDollarRisk,
            MinContracts: 1,
            MaxContracts: 3, // Limit maximum
            RiskPerTrade: 1000.0, // Enough for 16 contracts
            MethodParameters: new()
        );
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(3); // Applied maximum
        result.RiskAmount.Should().Be(187.5); // 3 * 5 * $12.50
        result.Calculations["optimal_contracts"].Should().Be(16.0);
        result.Calculations["clamped_contracts"].Should().Be(3);
    }
    
    [Fact]
    public void CalculateSize_ZeroStopTicks_ShouldReturnZeroContracts()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(stopTicks: 0); // Invalid
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestSizingConfig(SizingMethod.FixedDollarRisk);
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(0);
        result.RiskAmount.Should().Be(0);
        result.Calculations.Should().ContainKey("error");
    }
    
    [Fact]
    public void CalculateSize_InvalidIntent_ShouldReturnZeroContracts()
    {
        // Arrange - Create invalid intent
        var intent = new StrategyIntent(
            Symbol: "", // Invalid empty symbol
            Side: OrderSide.Buy,
            EntryType: OrderType.Market,
            LimitPrice: null,
            StopTicks: 10,
            TargetTicks: 20,
            Confidence: 0.8,
            Reason: "Test",
            Metadata: new()
        );
        
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestSizingConfig();
        
        // Act
        var result = _sizer.CalculateSize(intent, context, config);
        
        // Assert
        result.Contracts.Should().Be(0);
        result.RiskAmount.Should().Be(0);
        result.Calculations.Should().ContainKey("error");
    }
    
    [Fact]
    public void CalculateSize_WithNullParameters_ShouldThrow()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = TestDataBuilder.CreateTestSizingConfig();
        
        // Act & Assert
        Assert.Throws<ArgumentNullException>(() => _sizer.CalculateSize(null, context, config));
        Assert.Throws<ArgumentNullException>(() => _sizer.CalculateSize(intent, null, config));
        Assert.Throws<ArgumentNullException>(() => _sizer.CalculateSize(intent, context, null));
    }
    
    [Fact]
    public void CalculateSize_UnsupportedMethod_ShouldThrow()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent();
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.OptimalF, // Not supported in Phase 0
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: 200,
            MethodParameters: new()
        );
        
        // Act & Assert
        Assert.Throws<NotSupportedException>(() => _sizer.CalculateSize(intent, context, config));
    }
    
    [Fact]
    public void GetMetadata_ShouldReturnCorrectInformation()
    {
        // Act
        var metadata = _sizer.GetMetadata();
        
        // Assert
        metadata.Name.Should().Be("Basic Position Sizer");
        metadata.Description.Should().Contain("Fixed contracts");
        metadata.Description.Should().Contain("fixed dollar risk");
        metadata.RequiredParameters.Should().Contain("method");
        metadata.RequiredParameters.Should().Contain("risk_per_trade");
    }
    
    [Fact]
    public void ValidateConfig_ValidConfiguration_ShouldReturnTrue()
    {
        // Arrange
        var config = new SizingConfig(
            Method: SizingMethod.FixedContracts,
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: 200,
            MethodParameters: new() { ["contracts"] = 2 }
        );
        
        // Act
        var isValid = BasicPositionSizer.ValidateConfig(config, out var errors);
        
        // Assert
        isValid.Should().BeTrue();
        errors.Should().BeEmpty();
    }
    
    [Fact]
    public void ValidateConfig_InvalidConfiguration_ShouldReturnErrors()
    {
        // Arrange
        var config = new SizingConfig(
            Method: SizingMethod.FixedContracts,
            MinContracts: 5,
            MaxContracts: 2, // Invalid: min > max
            RiskPerTrade: -100, // Invalid: negative risk
            MethodParameters: new() // Missing required parameter
        );
        
        // Act
        var isValid = BasicPositionSizer.ValidateConfig(config, out var errors);
        
        // Assert
        isValid.Should().BeFalse();
        errors.Should().Contain("MinContracts must be <= MaxContracts");
        errors.Should().Contain("RiskPerTrade must be > 0");
        errors.Should().Contain("FixedContracts method requires 'contracts' parameter");
    }
    
    [Fact]
    public void GetSupportedSymbols_ShouldReturnAllSymbolsWithTickValues()
    {
        // Act
        var symbols = BasicPositionSizer.GetSupportedSymbols();
        
        // Assert
        symbols.Should().ContainKey("ES").WhoseValue.Should().Be(12.50);
        symbols.Should().ContainKey("MES").WhoseValue.Should().Be(1.25);
        symbols.Should().ContainKey("NQ").WhoseValue.Should().Be(5.00);
        symbols.Should().ContainKey("MNQ").WhoseValue.Should().Be(0.50);
        symbols.Should().ContainKey("CL").WhoseValue.Should().Be(10.00);
        symbols.Should().ContainKey("GC").WhoseValue.Should().Be(10.00);
        symbols.Count.Should().BeGreaterOrEqualTo(6);
    }
    
    [Fact]
    public void CalculateSize_ConsistentResults_ShouldBeDeterministic()
    {
        // Arrange
        var intent = TestDataBuilder.CreateValidIntent(symbol: "ES", stopTicks: 12);
        var context = TestDataBuilder.CreateTestContext();
        var config = new SizingConfig(
            Method: SizingMethod.FixedDollarRisk,
            MinContracts: 1,
            MaxContracts: 10,
            RiskPerTrade: 300,
            MethodParameters: new()
        );
        
        // Act - Calculate multiple times
        var results = new List<SizingResult>();
        for (int i = 0; i < 5; i++)
        {
            results.Add(_sizer.CalculateSize(intent, context, config));
        }
        
        // Assert - All results should be identical
        var firstResult = results[0];
        foreach (var result in results.Skip(1))
        {
            result.Contracts.Should().Be(firstResult.Contracts);
            result.RiskAmount.Should().Be(firstResult.RiskAmount);
            result.Method.Should().Be(firstResult.Method);
        }
    }
    
    public void Dispose()
    {
        // Cleanup if needed
    }
}
```

## 4. Implementation Summary

This implementation guide provides the exact content for all files required to implement the NT8 Institutional SDK Phase 0. When switching to Code mode, these files should be created in the specified paths with the provided content.

The implementation follows these key principles:
1. **Risk First**: All trades pass through risk management before execution
2. **Deterministic**: Identical inputs produce identical outputs for testing
3. **Modular**: Strategies are thin plugins, SDK handles infrastructure
4. **Observable**: Structured logging with correlation IDs throughout
5. **Test-Driven**: Comprehensive unit tests with >90% coverage

## 5. Next Steps

After implementing all files:
1. Create the solution and projects using dotnet CLI commands
2. Add required NuGet packages
3. Run the complete validation script
4. Verify all success criteria are met
5. Document SDK foundation and usage guidelines