Since #4441, the GoStdlibList action uses SUPPORTS_PATH_MAPPING_REQUIREMENT and passes the cache directory via add_all (which enables path mapping). This causes the stdlib builder to write path-mapped directory names (e.g. bazel-out/cfg/) into stdlib.pkg.json. The gopackagesdriver then reads these paths at runtime to open source files, but the mapped directory doesn't exist on disk — the actual files are under the real config directory (e.g. bazel-out/k8-fastbuild/).

This breaks the gopackagesdriver for any Go target:

error: unable to resolve imports: open .../bazel-out/cfg/bin/external/io_bazel_rules_go/stdlib_/gocache/...: no such file or directory

Affected stdlib packages are those with CGO-compiled files (net, os/user, internal/runtime/cgobench, etc.) whose CompiledGoFiles reference gocache entries under the mapped path.

Fix: Unlike the stdlib build action (_build_stdlib), the GoStdlibList action produces stdlib.pkg.json which is consumed at runtime by the gopackagesdriver — not by Bazel. Path mapping is not appropriate here because the mapped paths are never resolved back to real paths before being read. Revert to using cache_dir.path (real filesystem path) and remove SUPPORTS_PATH_MAPPING_REQUIREMENT from this action only.

This PR is an alternative to #4584 which tried to resolve this at the gopackagesdriver but that solution was deemed brittle.