fix(pkg): retire Nix-mirror per Guix-primary ruling (standards#101)

CONTRIBUTING.md

@@ -15,7 +15,7 @@ We welcome contributions in many forms:
 ## Getting Started
 
 1. **Read the AI Manifest:** Start with `0-AI-MANIFEST.a2ml` (if present) to understand the repository structure.
-2. **Environment:** Use `nix develop` or `direnv allow` to set up your tools.
+2. **Environment:** Use `guix shell -D -f guix.scm` (or `direnv allow`) to set up your tools. Guix is the canonical packager per [standards#101](https://github.com/hyperpolymath/standards/issues/101); the prior `nix develop` fallback was retired.
 3. **Task Runner:** Use `just` to see available commands (`just --list`).
 
 ## Development Workflow

TESTING-AUDIT.md

@@ -98,7 +98,7 @@ baseline, add a CI job that fails if p95 regresses > 50%.
 | **Functionality** | strong | 39 Elixir + 38 Rust test files, ~8,659 Elixir LOC, full pipeline E2E |
 | **Versability** | strong | SemVer in `CHANGELOG.adoc` + `mix.exs`, detailed per-version changelogs |
 | **Maintainability** | strong | Modular Rust workspace, TOPOLOGY.md, DESIGN-NARRATIVE.md, clean module boundaries |
-| **Reproducibility** | strong | `flake.nix` + `guix.scm`, `Cargo.lock` + `mix.lock` committed |
+| **Reproducibility** | strong | `guix.scm` (canonical per standards#101 — `flake.nix` retired), `Cargo.lock` + `mix.lock` committed |
 | **Portability** | strong | Cross-platform CI matrix (Linux x86_64 / ARM64, macOS x86_64 / ARM64, Windows), Containerfile, podman |
 | **Dependability** | weak | OTP supervision + concurrency tests but no chaos engineering, no fault-injection |
 | **Performance** | weak | No published metrics, no latency / throughput benchmarks gated, no capacity planning |