[zcbenz]

Close #3586.

The neural accelerator requires macOS 26.2 and with Xcode 26.5 we have to explicitly pass -mmacosx-version-min=26.2 to metal toolchain to compile NAX kernels correctly.

This PR does 2 things:

• Target 26.2 instead of 26.0 in CI.
• Target the host macOS version when MACOSX_DEPLOYMENT_TARGET is not set.

Note that strictly we should provide 2 distributions separately for 26.0 and 26.2 since the binaries would be different, but setuptools hard-codes plat name asmacosx_26_0 for wheels built for 26.x and I'm afraid the package managers also do the same, so users would be downloading binaries built for 26.2 on 26.0.

[scyyh11]

This matches what I found too. One extra detail that may be useful: the 26.2 workaround seems to line up with an ABI gate in the SDK 26.5 MPP headers.

With -mmacosx-version-min < 26.2, the cooperative tensor path lowers through the destination-tensor shim for all operands. With >= 26.2, it uses the indexed operand intrinsics. Comparing the same NAX kernel from the 0.31.2 wheel and my local SDK 26.5 build showed that intrinsic-family swap as the meaningful AIR difference.

I also tried a minimal accessor-only kernel. It is correct at min 26.2 and wrong at 26.0, so the shim path itself appears broken; using accessors alone probably would not save <26.2 builds.

Also checked: MLX's current hardcoded NAX layout matches the >=26.2 indexed layout.

[bri-prism]

Tested on M5 Pro relative error dropped to under 2e-5

[angeloskath]

🙏