Every new commit triggered a full workspace recompile (~6min for a 2-file
change) in ensure-binary. The binary cache at /data/bin/$SHA is SHA-keyed
so it misses on every new commit. The cargo incremental cache at
/cargo-target/target is file-mtime keyed, which git checkout invalidates
whenever it retouches files.
sccache (already present in ci-builder image, verified via `sccache --version`
in Dockerfile) is content-hash keyed — identical source → identical hit
regardless of mtime. Sits in front of rustc via RUSTC_WRAPPER. Cache dir
on the same cargo-target-cuda PVC (SCCACHE_DIR=/cargo-target/sccache) so:
- Combines with cargo's target/ cache on one volume, no separate PVC
- Disk-local hits, no network round-trip per rustc invocation
- Survives across pods and commits — the git-checkout mtime flip that
breaks cargo's fingerprints doesn't affect content-hash caching
40G cache size cap — the cargo-target-cuda PVC is large enough that
sccache won't evict useful entries under normal use.
Expected behaviour: first build after this commit is still a full rebuild
(sccache cache empty). Subsequent builds for the same CUDA_COMPUTE_CAP
should hit compiled objects at near-zero cost for crates whose source
hasn't changed.
Applied to cluster via `kubectl apply -n foxhunt -f` — WorkflowTemplate
is live before the next ./scripts/argo-train.sh invocation.
Closes task #34.
8afe9562e5