onnx-runtime-ep-cpu

The CPU execution provider for the ORT 2.0 runtime (see docs/ORT2.md §4.4 and §54 Phase 1). It implements [onnx_runtime_ep_api::ExecutionProvider] and hosts pure-Rust reference kernels for the Phase-1 op set (MatMul, Add, Relu, Reshape, Transpose, Gather, LayerNormalization).

Correctness first, perf later

The Phase-1 exit milestone is a correctness goal ("BERT on CPU matches upstream ORT"), so these kernels are straightforward, naive pure-Rust implementations — no C++/FFI, no oneDNN, no cc build dependency (oneDNN is not installed on the build host). Each kernel lives behind the [onnx_runtime_ep_api::Kernel] trait, leaving a clean seam for a Phase-1.5 perf pass to drop in a blocked/SIMD GEMM (oneDNN via FFI, or a Rust BLAS such as matrixmultiply/gemm) without disturbing the EP contract or the session. See [kernels::matmul] for the hot spot.

unsafe

The crate is unsafe-minimal. The only unsafe is the raw device-buffer access the ep-api contract forces (aligned host alloc/dealloc, memcpy, and strided element reads/writes), each isolated and SAFETY-documented. All kernel arithmetic is safe Rust operating on dense Vec<f32> buffers produced by the two audited accessors in [kernels].