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docs/net40-amalgamation.md

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+# .NET 4.0 Amalgamation
+
+Legacy .NET 4.0 consumers should use the amalgamated source model.
+
+## Files
+
+- `AmalgamationTool/DynamORM.Amalgamation.cs`: merged source file.
+- `DynamORM.Net40.csproj`: net40 build project that compiles the amalgamation output.
+
+## Regenerate Amalgamation
+
+The amalgamation file must be regenerated after library source changes.
+
+Current workflow in this repository:
+
+1. Build or run `AmalgamationTool` (or use an equivalent merge script).
+2. Merge all files from `DynamORM/` into `AmalgamationTool/DynamORM.Amalgamation.cs`.
+3. Build `DynamORM.Net40.csproj`.
+
+## Build in Mono Container
+
+```bash
+docker run --rm -v "$PWD":/src -w /src mono:latest \
+  bash -lc "msbuild /t:Build /p:Configuration=Release DynamORM.Net40.csproj"
+```
+
+Expected output artifact:
+
+- `bin/Release/net40/DynamORM.Net40.dll`
+
+## Build with .NET SDK Container
+
+```bash
+docker run --rm -v "$PWD":/src -w /src mcr.microsoft.com/dotnet/sdk:10.0-preview \
+  dotnet build DynamORM.Net40.csproj -c Release
+```
+
+## Important Constraint
+
+Do not force net40 into the main multi-target `DynamORM/DynamORM.csproj` for modern workflows.
+
+Keep net40 compatibility validated through the dedicated amalgamation project so legacy consumers can embed the single-file source without destabilizing primary targets.