diff --git a/flake.nix b/flake.nix
deleted file mode 100644
index 5c7d327..0000000
--- a/flake.nix
+++ /dev/null
@@ -1,34 +0,0 @@
-# SPDX-License-Identifier: MPL-2.0
-# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell
-#
-# Development environment for verisimdb.
-#
-# Estate policy is Guix primary / Nix fallback (hyperpolymath/standards).
-# This is the Nix fallback tier. It is a dev shell, not a package build:
-# it declares the toolchain needed to work on this repo, pinned to an
-# exact nixpkgs revision per the estate SHA-pinning rule.
-#
-# Packages mirror the build tooling actually present in this repo
-# (just rust) — not a generic estate default.
-#
-#   nix develop      # enter the shell
-#   nix flake check  # verify this file evaluates (run before committing)
-{
-  description = "verisimdb development environment";
-
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/b134951a4c9f3c995fd7be05f3243f8ecd65d798";
-
-  outputs = { self, nixpkgs }:
-    let
-      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
-      forAllSystems = f:
-        nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
-    in
-    {
-      devShells = forAllSystems (pkgs: {
-        default = pkgs.mkShell {
-          packages = with pkgs; [ just cargo rustc rustfmt clippy ];
-        };
-      });
-    };
-}
diff --git a/guix.scm b/guix.scm
new file mode 100644
index 0000000..47d7b9d
--- /dev/null
+++ b/guix.scm
@@ -0,0 +1,53 @@
+;; SPDX-License-Identifier: MPL-2.0
+;; SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+;;
+;; Guix development manifest for VeriSimDB.
+;;
+;;     guix shell -m guix.scm
+;;
+;; SCOPE — read this before extending the file.
+;;
+;; This is a *development environment* manifest, not a package definition. It
+;; replaces the `flake.nix` dev shell removed in the same change, one-for-one:
+;; that file declared a toolchain, not a build, and said so in its own header.
+;; Nothing that existed before is lost by this swap.
+;;
+;; It is deliberately NOT a `(package ...)` with `cargo-build-system`. VeriSimDB
+;; is a 17-crate Rust workspace plus an Elixir/OTP layer; a correct
+;; `#:cargo-inputs` enumeration would need every transitive crate pinned, and a
+;; definition that merely *looks* like a package build while failing to produce
+;; one would be worse than this honest manifest — the estate already has enough
+;; artefacts that satisfy a presence check without doing anything. Promote this
+;; to a real package definition when someone can build and verify it end to end.
+;;
+;; NOT VALIDATED LOCALLY: Guix is not installed on the authoring machine, so
+;; this file has not been evaluated. Run `guix shell -m guix.scm -- true` before
+;; relying on it, and fix rather than delete it if a specification name has
+;; drifted.
+;;
+;; Toolchain rationale — each entry maps to something this repo actually uses:
+;;
+;;   rust, rust:cargo   17-crate workspace under rust-core/ (Cargo.toml)
+;;   rust:rustfmt       `cargo fmt` is enforced in CI
+;;   elixir, erlang     elixir-orchestration/ (mix, 647 tests)
+;;   coq                formal/ — 9 modules, gated by coq-build.yml
+;;   just               formal/Justfile and the root justfile
+;;   reuse              REUSE compliance is a required check (776/776)
+;;   git, gnu-make      assumed by several recipes
+;;
+;; Deliberately absent: Node, npm, Deno and friends. This repo's own
+;; NPM/Bun Blocker and TypeScript/JavaScript Blocker workflows reject them, and
+;; a template-supplied toolchain that installed them is exactly the class of
+;; drift those gates exist to catch.
+
+(specifications->manifest
+ (list "rust"
+       "rust:cargo"
+       "rust:rustfmt"
+       "elixir"
+       "erlang"
+       "coq"
+       "just"
+       "reuse"
+       "git"
+       "gnu-make"))