C# bridge development

Run Rust commands from baml_language:

RUSTC_WRAPPER= cargo test -p sdkgen_csharp --lib
RUSTC_WRAPPER= cargo test -p bex_engine --test opaque_resource_handles
RUSTC_WRAPPER= cargo test -p sdk_test_csharp generated_baml_clients_are_not_tracked --lib

The full C# fixture suite is prepared by sdk_test_harness_setup; it invokes the public C# generation facade twice and verifies deterministic manifests before running the .NET consumers. Generated fixture clients are disposable test output and must remain untracked.

For a canonical-schema change, build bridge_ctypes to refresh its Rust and Python consumers, then regenerate and verify the checked-in C++ client:

RUSTC_WRAPPER= cargo build -p bridge_ctypes
RUSTC_WRAPPER= cargo test -p sdkgen_cpp --test pb_generation regenerate -- --ignored --exact
RUSTC_WRAPPER= cargo test -p sdkgen_cpp --test pb_generation

The C# project generates its protobuf classes during dotnet build. The Baml.Bridge.ProtocolProbe project is the direct C# schema consumer. The emit_optional_host_call_vectors binary belongs to the C# SDK test crate and supplies Rust-produced callback vectors to that probe.

bridge_csharp/src/Values/BamlUnion.cs is a checked-in mechanical runtime source. Regenerate it after changing the union surface, then verify that the checked-in bytes match the C#-owned generator:

dotnet run --project sdks/csharp/bridge_csharp/tools/Baml.UnionGenerator/Baml.UnionGenerator.csproj --configuration Release -- --write sdks/csharp/bridge_csharp/src/Values/BamlUnion.cs
dotnet run --project sdks/csharp/bridge_csharp/tools/Baml.UnionGenerator/Baml.UnionGenerator.csproj --configuration Release -- --check sdks/csharp/bridge_csharp/src/Values/BamlUnion.cs

The generator emits arities 2 through 32 deterministically with UTF-8 and LF line endings. The C# SDK test crate runs the same drift check in CI.

Release platform metadata declares artifacts.cffi and artifacts.csharp as sibling records. C# entries name the RID-local native asset and require the generic CFFI artifact for the same target; a generic CFFI target does not imply a C# package. build2-bridge-cffi.reusable.yaml produces only generic native artifacts containing the library and its checksum. Actions artifacts are workflow-run scoped; C# records source SHA, canonical version, workflow run ID, target, producer filename, runtime path, and digest when it assembles the package. Provenance deliberately excludes github.run_attempt, so rerunning failed jobs can reuse successful producers from an earlier attempt of the same run. Unrelated future CFFI-only artifacts are ignored.

prepare-csharp-sdk.reusable.yaml prepares platform-neutral generated and ABI inputs in parallel with the CFFI matrix. verify-csharp-product-slice.reusable.yaml assembles and exercises the required RID set from the validated platform contract, and publish2-csharp-sdk.yaml publishes that exact verified package. On a repair rerun, the publisher removes only NuGet's repository signature from the comparison model and skips an identical existing package; a product-owned content mismatch remains fatal.