pass revision to to cmake template

[drbh]

This PR fixes a bug where the ops id was not passed to render_preamble, causing it to fall back to a different identifier in Nix builds. This made the cmake extension name diverge from the expected name.

Additionally, the postInstall cleanup pattern was missing the backend segment, so stale build artifacts were not removed. Together these caused build-and-copy to fail with Permission denied when bundling multiple variants.

error when using the builder on main

nix flake update
nix run .#build-and-copy -L --cores 2 --max-jobs 8
# torch-ext-bundle> cp: cannot create regular file '/nix/store/i0lf882dgvi9ffgc1sq92s0n330w3ynl-torch-ext-bundle/_flash_mla_cuda_ghzc76n4to3fq/_flash_mla_cuda_ghzc76n4to3fq.abi3.so': Permission denied
# error: Cannot build '/nix/store/ijd011d4pz5jy56m2c2q21fmrhnyjml9-torch-ext-bundle.drv'.
#        Reason: builder failed with exit code 1.
#        Output paths:
#          /nix/store/i0lf882dgvi9ffgc1sq92s0n330w3ynl-torch-ext-bundle
#        Last 1 log lines:
#        > cp: cannot create regular file '/nix/store/i0lf882dgvi9ffgc1sq92s0n330w3ynl-torch-ext-bundle/_flash_mla_cuda_ghzc76n4to3fq/_flash_mla_cuda_ghzc76n4to3fq.abi3.so': Permission denied
#        For full logs, run:
#          nix log /nix/store/ijd011d4pz5jy56m2c2q21fmrhnyjml9-torch-ext-bundle.drv
# error: Cannot build '/nix/store/dmwahvzhw1vsy2kqvz39sipv81x3iws0-build-and-copy.drv'.
#        Reason: 1 dependency failed.
#        Output paths:
#          /nix/store/pwsp646ri9y2c61azk9smqm4n8j37fa9-build-and-copy
# ❌ /nix/store/dmwahvzhw1vsy2kqvz39sipv81x3iws0-build-and-copy.drv^out
# error: Build failed due to failed dependency

example of build output when using an older version of the builder that didnt cause the collision but didnt clean up the build artifacts

# set kernel-builder.url = "github:huggingface/kernels/2c436beccd9adf962f1634c45e825e69909768c6";
tree -L 1 build
# build
# ├── _flash_mla_cuda_ffxujicuwi76y
# ├── _flash_mla_cuda_hu5pgjzy2nejw
# ├── _flash_mla_cuda_lsxvehlvaijjo
# ├── _flash_mla_cuda_syrdugbz4gcrc
# ├── torch210-cxx11-cu128-x86_64-linux
# ├── torch210-cxx11-cu130-x86_64-linux
# ├── torch29-cxx11-cu128-x86_64-linux
# └── torch29-cxx11-cu130-x86_64-linux

example build after changes

# set kernel-builder.url = "path:/home/drbh/Projects/kernels";
nix run .#build-and-copy -L --cores 2 --max-jobs 8
tree -L 1 build
# build
# ├── torch210-cxx11-cu128-x86_64-linux
# ├── torch210-cxx11-cu130-x86_64-linux
# ├── torch29-cxx11-cu128-x86_64-linux
# └── torch29-cxx11-cu130-x86_64-linux

note: upon further investigation the collision seems to happen after #281 which seemed to result in the same identifier being used in multiple variants which resulted in a conflict in the join-paths merge. the changes in this PR avoid this bug and result in a reliable build output

[danieldk]

Great catch! Merging immediately, since we are often building using main.