The libsodium-sys-stable build.rs panics if both SODIUM_LIB_DIR and
SODIUM_USE_PKG_CONFIG are set simultaneously. The runner infrastructure
at 172.0.0.29 has SODIUM_USE_PKG_CONFIG in its container environment
(not traceable to any workflow file or Docker image ENV layer), which
conflicts with the SODIUM_LIB_DIR approach used for cross-compilation.
Explicitly unset SODIUM_USE_PKG_CONFIG in the shell before npm/cargo
runs on all three platforms (linux-amd64, windows-amd64, linux-arm64)
in both release-beta.yml and auto-tag.yml. This is a defensive no-op
when the variable is absent, and a clean fix when it is present.