Go: a full run grows GOCACHE without bound (235 GB) and fills the disk #17

What happens

A full run over a large Go codebase filled the disk. About 33,000 mutation sites in 65 packages ran for roughly 5 hours. Go's build cache (go env GOCACHE, ~/Library/Caches/go-build on macOS) grew to 235 GB. The disk reached 0 bytes free, and later packages failed with [Errno 28] No space left on device. Other processes on the machine failed too.

Why

Every mutant changes one source file, so go test compiles a new package archive and links a new test binary. Each binary is cached under a fresh key. With thousands of mutants per package, the cache grows by gigabytes per package and is never trimmed: Go's own trimming removes only entries unused for 5 days.

Workaround

Run with a private cache and remove it after each package:

GOCACHE=$PWD/target/gocache mutator ... ; go clean -cache

Suggestion

One of these, from simplest:

1. Mention the disk cost in the README's Go section, together with the workaround.
2. Give the mutant runs a cache under the run directory (target/mutation-workers/run-*/gocache), seeded from the user's cache or shared across workers, and delete it with the run.
3. Run go clean -cache with GOCACHE set to the private cache between files.

Option 2 keeps dependency builds warm within a run and bounds disk use to one run.

Environment

mutator a5a0cb8, Go 1.27.1, macOS arm64, --max-workers 14.