Content-addressed SDK unpack on Darwin fails

On nixpkgs-unstable at aa9461550594533c29866d42f861b6ff079a7fb6, on aarch64-darwin, with contentAddressedByDefault = true:

> nix log /nix/store/nv3wn7aps3mf18cadx0gxrpydi6kv1wf-MacOSX-SDK-11.0.0.drv                                                                                                                                                                                          
warning: The interpretation of store paths arguments ending in `.drv` recently changed. If this command is now failing try again with '/nix/store/nv3wn7aps3mf18cadx0gxrpydi6kv1wf-MacOSX-SDK-11.0.0.drv^*'
sourcing setup hook '/nix/store/h9lc1dpi14z7is86ffhl3ld569138595-audit-tmpdir.sh'
sourcing setup hook '/nix/store/m54bmrhj6fqz8nds5zcj97w9s9bckc9v-compress-man-pages.sh'
sourcing setup hook '/nix/store/wgrbkkaldkrlrni33ccvm3b6vbxzb656-make-symlinks-relative.sh'
sourcing setup hook '/nix/store/5yzw0vhkyszf2d179m0qfkgxmp5wjjx4-move-docs.sh'
sourcing setup hook '/nix/store/fyaryjvghbkpfnsyw97hb3lyb37s1pd6-move-lib64.sh'
sourcing setup hook '/nix/store/kd4xwxjpjxi71jkm6ka0np72if9rm3y0-move-sbin.sh'
sourcing setup hook '/nix/store/pag6l61paj1dc9sv15l7bm5c17xn5kyk-move-systemd-user-units.sh'
sourcing setup hook '/nix/store/jivxp510zxakaaic7qkrb7v1dd2rdbw9-multiple-outputs.sh'
sourcing setup hook '/nix/store/ilaf1w22bxi6jsi45alhmvvdgy4ly3zs-patch-shebangs.sh'
sourcing setup hook '/nix/store/cickvswrvann041nqxb0rxilc46svw1n-prune-libtool-files.sh'
sourcing setup hook '/nix/store/xyff06pkhki3qy1ls77w10s0v79c9il0-reproducible-builds.sh'
sourcing setup hook '/nix/store/ngg1cv31c8c7bcm2n8ww4g06nq7s4zhm-set-source-date-epoch-to-latest.sh'
sourcing setup hook '/nix/store/gps9qrh99j7g02840wv5x78ykmz30byp-strip.sh'
@nix { "action": "setPhase", "phase": "unpackPhase" }
Running phase: unpackPhase
/nix/store/ns0m3hrb2xzkn2pwdhlmmski610dmrsn-bootstrap-stage0-stdenv-darwin/setup: line 1654: 27432 Killed: 9               pbzx $src
     27433                       | cpio -idm

The failing line of code appears to be nixpkgs/pkgs/os-specific/darwin/apple-sdk-11.0/default.nix at ec661559fc70ae4ba5ae28e012bf9f7d22ac14b1 · NixOS/nixpkgs · GitHub

I can build the SDKs locally without contentAddressedByDefault (as verified with nix-build --check).

I’m observing this by building #patrick from GitHub - Smaug123/nix-dotfiles: Dotfiles for my Nix setup at commit ad9621acd31f5c1b6d30f286e550f1849e3a0472 .

What information would help me or anyone else debug this?