Add CLAUDE.md for project guidance and documentation

Author: koenbeuk

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+EntityFrameworkCore.Triggered is a library that adds trigger support (before/after save hooks) to Entity Framework Core. Triggers react to entity changes during `SaveChanges` via `IBeforeSaveTrigger<T>`, `IAfterSaveTrigger<T>`, and related interfaces.
+
+## Build & Test Commands
+
+```bash
+# Build (default is V3 / .NET 6.0)
+dotnet build EntityFrameworkCore.Triggered.sln
+
+# Run all tests
+dotnet test EntityFrameworkCore.Triggered.sln
+
+# Run a single test project
+dotnet test test/EntityFrameworkCore.Triggered.Tests
+
+# Run a specific test
+dotnet test test/EntityFrameworkCore.Triggered.Tests --filter "FullyQualifiedName~TriggerSessionTests.RaiseBeforeSaveTriggers"
+
+# Build for V2 (.NET Standard 2.1)
+dotnet build EntityFrameworkCore.Triggered.sln -c ReleaseV2
+
+# Build for V1 (.NET Standard 2.0)
+dotnet build EntityFrameworkCore.Triggered.sln -c ReleaseV1
+
+# Pack NuGet packages
+dotnet pack EntityFrameworkCore.Triggered.sln -c Release
+```
+
+## Architecture
+
+### Project Dependency Graph
+
+```
+Abstractions  <──  Core (EntityFrameworkCore.Triggered)  <──  Extensions
+                                                          <──  Transactions
+Transactions.Abstractions  <──  Transactions
+```
+
+- **Abstractions**: Pure interfaces (`IBeforeSaveTrigger<T>`, `IAfterSaveTrigger<T>`, `ITriggerContext<T>`, `ITriggerSession`, `ChangeType`, lifecycle triggers). No EF Core dependency.
+- **Core**: Main implementation — `TriggerSession` (orchestrator, ~400 lines), `TriggerService`, `TriggerContext`, trigger discovery, cascade strategies, and EF Core integration via `UseTriggers()`.
+- **Extensions**: Assembly scanning for trigger discovery (`AddAssemblyTriggers`).
+- **Transactions**: Transaction-scoped triggers (`IBeforeCommitTrigger`, `IAfterCommitTrigger`).
+
+### Key Internal Components
+
+- **TriggerSession** (`src/EntityFrameworkCore.Triggered/TriggerSession.cs`): Core orchestrator that coordinates trigger discovery, invocation, and cascading during SaveChanges.
+- **TriggerContextTracker** (`Internal/`): Wraps EF Core's ChangeTracker to discover pending entity changes.
+- **TriggerDiscoveryService** (`Internal/`): Resolves registered triggers for entity types, supporting type inheritance and priority ordering.
+- **Descriptor classes** (`Internal/Descriptors/`): Handle invocation of specific trigger types (BeforeSave, AfterSave, etc.) via reflection.
+- **CascadeStrategies** (`Internal/CascadeStrategies/`): Control re-discovery of changes after triggers modify entities. Default is `EntityAndTypeCascadeStrategy`.
+
+### Registration Entry Points
+
+- `UseTriggers()` on `DbContextOptionsBuilder` — core configuration
+- `AddTriggeredDbContext<T>()` / `AddTriggeredDbContextPool<T>()` / `AddTriggeredDbContextFactory<T>()` — service collection helpers in `Extensions/ServiceCollectionExtensions.cs`
+
+## Multi-Version Strategy
+
+The project supports multiple EF Core versions via build configurations and conditional compilation:
+
+| Config | Target | Preprocessor Symbol | EF Core |
+|--------|--------|---------------------|---------|
+| Release (V3) | net6.0 | `EFCORETRIGGERED3` | 6.0.0 |
+| ReleaseV2 | netstandard2.1 | `EFCORETRIGGERED2` | 3.1.x |
+| ReleaseV1 | netstandard2.0 | `EFCORETRIGGERED1` | 3.1.x |
+
+Version-specific code uses `#if EFCORETRIGGERED3` guards. The current branch (`v3`) targets V3.
+
+## Build Settings
+
+- **TreatWarningsAsErrors**: enabled globally (`Directory.Build.props`)
+- **Nullable reference types**: enabled
+- **LangVersion**: 9.0
+- **Strong naming**: enabled (signed with `EntityFrameworkCore.Triggered.snk`)
+
+## Test Projects
+
+- `EntityFrameworkCore.Triggered.Tests` — unit tests (xUnit), uses EF Core InMemory provider
+- `EntityFrameworkCore.Triggered.IntegrationTests` — full SaveChanges lifecycle tests
+- `EntityFrameworkCore.Triggered.Extensions.Tests` — assembly trigger discovery
+- `EntityFrameworkCore.Triggered.Transactions.Tests` — transaction trigger behavior
+- `EntityFrameworkCore.Triggered.Analyzers.Tests` — Roslyn analyzer tests