Add Linux arm64 support to the SDK v2 packaging pipelines

[baijumeswani]

Adds first-class Linux arm64 support across the SDK v2 build, test, and packaging pipelines. Every package format the pipeline already produces (C++ tgz, Runtime NuGet, Python wheel, npm tarball) now includes a linux-arm64 payload, built and tested natively on the onnxruntime-linux-ARM64-CPU-2019 pool.

Initial Linux ARM64 support is CPU-only.

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Project	Deployment	Actions	Updated (UTC)
foundry-local	Ready	Preview, Comment	Jul 22, 2026 8:34pm

[Copilot]

Pull request overview

Adds native CPU-only Linux ARM64 support across SDK v2 build, test, and packaging workflows.

Changes:

• Adds ARM64 native builds and C++, C#, Python, and JavaScript test stages.
• Packages Linux ARM64 binaries in C++ archives, NuGet, Python wheels, and npm tarballs.
• Updates runtime detection, dependency selection, WebGPU fallback behavior, tests, and documentation.

Reviewed changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk_v2/python/test/unit/test_lib_loader.py	Tests ARM64 platform detection.
sdk_v2/python/test/unit/test_build_backend.py	Tests dependency-pin rewriting.
sdk_v2/python/src/foundry_local_sdk/_native/lib_loader.py	Detects Linux ARM64 payloads.
sdk_v2/python/pyproject.toml	Adds CPU-only ARM64 dependencies.
sdk_v2/python/_build_backend/__init__.py	Rewrites plain ORT package pins.
sdk_v2/js/script/install-native.cjs	Supports ARM64 and fails on missing payloads.
sdk_v2/cpp/triplets/arm64-linux.cmake	Defines the ARM64 vcpkg triplet.
sdk_v2/cpp/test/internal_api/webgpu_ep_bootstrapper_test.cc	Adds WebGPU bootstrapper tests.
sdk_v2/cpp/test/CMakeLists.txt	Registers the new C++ test file.
sdk_v2/cpp/src/ep_detection/webgpu_ep_bootstrapper.h	Documents ARM64 WebGPU behavior.
sdk_v2/cpp/src/ep_detection/webgpu_ep_bootstrapper.cc	Gracefully disables unavailable ARM64 WebGPU.
sdk_v2/cpp/nuget/test_pack.py	Tests NuGet staging and RID mapping.
sdk_v2/cpp/nuget/pack.py	Stages the Linux ARM64 runtime.
sdk_v2/cpp/nuget/Microsoft.AI.Foundry.Local.Runtime.nuspec	Documents the ARM64 payload.
sdk_v2/cpp/cmake/FindOnnxRuntimeGenAI.cmake	Selects ARM64 GenAI binaries.
sdk_v2/cpp/cmake/FindOnnxRuntime.cmake	Selects CPU-only ARM64 ORT binaries.
.pipelines/v2/templates/steps-test-python.yml	Supports system Python on ARM64 agents.
.pipelines/v2/templates/steps-test-js.yml	Enables Linux ARM64 JavaScript tests.
.pipelines/v2/templates/steps-pack-nuget.yml	Includes the ARM64 native artifact.
.pipelines/v2/templates/steps-pack-js.yml	Merges the ARM64 npm prebuild.
.pipelines/v2/templates/steps-pack-cpp-sdk.yml	Produces an ARM64 C++ archive.
.pipelines/v2/templates/steps-build-python.yml	Supports ARM64 system Python builds.
.pipelines/v2/templates/steps-build-linux.yml	Parameterizes Linux CPU architecture.
.pipelines/v2/templates/steps-build-js.yml	Builds and stages ARM64 Node addons.
.pipelines/v2/templates/stages-python.yml	Adds ARM64 Python build and test stages.
.pipelines/v2/templates/stages-js.yml	Adds ARM64 JavaScript build and test stages.
.pipelines/v2/templates/stages-cs.yml	Adds ARM64 C# testing.
.pipelines/v2/templates/stages-build-native.yml	Adds native ARM64 build and packaging inputs.
.pipelines/v2/sdk_v2-pipeline-plan.md	Documents the expanded pipeline matrix.
.pipelines/v2/sdk_v2-js-pipeline-plan.md	Documents ARM64 JavaScript packaging.

[prathikr]

Can you add to the PR description all the new unit tests that have been introduced and their purposes?