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+# Project Euler - C# Solutions
+
+## Build & Test
+```bash
+dotnet build Euler.sln
+dotnet test EulerLibTests/EulerLibTests.csproj
+```
+
+## Structure
+- **Euler/** - Console runner app (net8.0)
+- **EulerLib/** - Problem solutions library. Each problem implements `IProblem` (`Id`, `Title`, `Solve()`, `Md5OfSolution`)
+- **EulerLibTests/** - Test project (NUnit + FluentAssertions + AutoFixture)
+
+## Conventions
+- Problems go in `EulerLib/Problems/0001_0100/Problem0001.cs` (namespace `EulerLib.Problems`)
+- Tests go in `EulerLibTests/Problems/0001_0100/Problem0001Fixture.cs` (namespace `EulerLibTests.Problems`)
+- Problem input data files go in `ContentFiles/` (lib) or `TestFiles/` (tests), copied to output via csproj
+- `SoakTestFixture` validates all solutions via MD5 hash - never commit a broken `Md5OfSolution`
+- TreatWarningsAsErrors is enabled in Debug builds