Should releases include a native win-arm64 binary?

[tig]

Question

Should release builds include a native win-arm64 binary?

Current state

The release matrix (.github/workflows/release.yml) builds three RIDs, one per OS at its dominant arch:

• osx-arm64
• linux-x64
• win-x64

There is no win-arm64 (nor linux-arm64 / osx-x64). The implicit policy today is "one RID per OS, the dominant architecture."

Why this is deferred, not an oversight

Windows-on-ARM already runs the win-x64 binary. WoA ships a built-in x64 emulator, so clet-<ver>-win-x64.zip is functional on Snapdragon X / ARM Surface devices today. The case for a native win-arm64 build is therefore performance (cold-start latency under emulation), not functionality. Our own perf budget cares about this (tests/SPEC.md: "<150ms Windows x64"), but for the current alpha (one clet) it's premature.

The build cost is non-trivial because of AOT. We publish with -p:PublishAot=true --self-contained. ILC cross-compilation to win-arm64 from a win-x64 host is not a clean path; the reliable approach is a native windows-11-arm GitHub runner (now GA). That means a new matrix row, a new runner, and getting the Unit/Integration/Smoke steps green on arm64. Note tests/Directory.Build.props already documents a win-arm64 sharp edge (NETSDK1151), so the RID has its own known rough spots.

Adding it breaks the current symmetry and invites "then why not linux-arm64?" — which should be a deliberate coverage decision, not a one-off.

When it would be worth doing

• Once there's actual user demand for native Windows ARM performance, or
• When we stand up the Homebrew/WinGet channels at v1.0 GA (Milestone: v1.0 GA — tied to TG v2 GA, channels live #6) and want first-class arm64 packages rather than emulated ones — that's the natural moment, since we're touching the release/packaging surface anyway.

Proposed disposition

Defer past v0.x. Revisit at RC (#5) / GA (#6). If accepted, the work is:

• Add a win-arm64 row to the build matrix in release.yml on a windows-11-arm runner.
• Confirm AOT publish + Unit/Integration/Smoke pass on arm64.
• Add package_windows win-arm64 to the release packaging step and a row to the README download table.
• Update specs/clet-spec.md §7 (release) to record the supported-RID policy explicitly.