test(workload): establish binary and OCI packaging entry gate

[darwin67]

Summary

• define one canonical deterministic workload model for standalone binaries and OCI images
• retain raw source evidence and derived guest content as an independently verifiable replay closure
• specify unprivileged per-invocation execution, live workload I/O, whole-guest cleanup, OCI normalization, and private artifact boundaries
• complete the RFD 3 entry gate with an auditable standalone C workload fixture
• reproducibly capture the fixture as both a static x86-64 Linux ELF and a minimal local OCI image layout
• record artifact identities, sizes, constraints, and validation evidence without prematurely selecting parser or cache limits

Entry-gate regression coverage

• accepts independently generated RFD 2 payloads over an exact one-block TFTP exchange and rejects corruption
• permits only one escaped descriptor-retaining descendant per invocation
• runs concurrent captures into distinct directories and recursively compares every generated file

Oracle review

Two review-and-fix passes resolved RFD 2 payload incompatibility, unbounded descendant creation, unsafe shared capture publication, and the capture-comparison precision gap. Oracle's final review reported no findings.

Validation

• .agents/dev ./scripts/rfd3-entry-gate-test.sh
• .agents/dev make check-rfds
• .agents/dev cargo fmt --all -- --check
• .agents/dev cargo clippy --workspace --all-targets -- -D warnings
• .agents/dev cargo test --workspace --all-targets (83 tests)
• nix --extra-experimental-features 'nix-command flakes' flake check
• bash -n scripts/*.sh
• shellcheck scripts/rfd3-entry-gate.sh scripts/rfd3-entry-gate-test.sh