refactor(root): move root artefacts to their canonical locations

.github/CONTRIBUTING.md

@@ -0,0 +1,91 @@
+# Contributing to echo-types
+
+Thank you for your interest. Echo-types is a constructive Agda
+formalisation; contribution discipline reflects the proof-bearing nature
+of the codebase.
+
+## Sign-off
+
+All commits require Developer Certificate of Origin sign-off:
+
+    git commit -s -m "feat: ..."
+
+## Branches
+
+- `main` — protected; only fast-forward from approved PRs.
+
+- `feat/<topic>` — feature branches, squash-merge.
+
+- `fix/<topic>` — bug-fix branches.
+
+## Pre-merge checklist
+
+1.  `just` `verify` passes (full Agda type-check pass against
+    `proofs/agda/All.agda` and the test suites).
+
+2.  CHANGELOG.md updated under `[Unreleased]`.
+
+3.  `.machine_readable/6a2/STATE.a2ml` `last-updated` bumped if the
+    change is significant.
+
+4.  **Banned constructs.** No new `believe_me`, `assert_total`,
+    `postulate`, `sorry`, `Admitted`, `unsafeCoerce`, or `Obj.magic`
+    introduced. Estate-wide policy.
+
+5.  **Guardrails are CI-enforced.** All `.agda` files under
+    `proofs/agda/**` must declare `{-#` `OPTIONS` `--safe` `--without-K`
+    `#-}` at the top. `tools/check-guardrails.sh` runs at CI time across
+    every file (regardless of `All.agda` membership) and fails on:
+    missing `--safe` / `--without-K`, escape pragmas (`TERMINATING`,
+    `REWRITE`, `NO_POSITIVITY_CHECK`, etc.), `postulate` in code, or
+    unsafe primitives (`primTrustMe`, `primEraseEquality`, `trustMe`).
+    The `Exploratory` classification in
+    `docs/echo-types/echo-kernel-note.adoc` only excuses `All.agda`
+    membership — it does NOT excuse the guardrail. If you need
+    postulates for a demo or earn-back-gate consumer, the file must live
+    outside `proofs/agda/` (no current non-guarded path exists; widening
+    the guardrail’s allowlist requires a separate design discussion).
+
+6.  **EI-2 discipline.** Per `.machine_readable/6a2/STATE.a2ml` `§`
+    `ei-2`, the integration-recipe distinctness investigation is
+    *terminated negatively* and is not to be reopened. If a change
+    touches that territory, read `STATE.a2ml` `§` `ei-2` first; the
+    `forbidden-rebrandings` list is a hard fence.
+
+7.  **Naming traps.** `ModeGraded` (with trailing `d`) is canonical;
+    never `ModeGrade`. See `STATE.a2ml` `§` `naming-traps`.
+
+## Reviews
+
+At least one maintainer review (see MAINTAINERS.adoc). Bridge-module
+changes (the cross-system bridges in `proofs/agda/Echo*Bridge*.agda`)
+need attention because they fix the load-bearing distinctness story;
+flag them for explicit review.
+
+## Contribution model — Tri-Perimeter Contribution Framework (TPCF)
+
+echo-types follows the estate-wide **Tri-Perimeter Contribution
+Framework (TPCF)** — graduated trust without gatekeeping:
+
+- **Perimeter 1 — Core Systems (maintainers only).** The proof kernel:
+  `proofs/agda/Echo.agda`, the identity-claim spine, the bridge modules,
+  the `All.agda` / `Smoke.agda` wiring, and the guardrail tooling.
+  Direct commits by maintainers only.
+
+- **Perimeter 2 — Expert Extensions (trusted contributors).** New proof
+  modules, decoration instances, and ordinal-track slices. Apply via
+  issue → review → merge under the relevant `proofs/agda/` path with the
+  build invariant green.
+
+- **Perimeter 3 — Community Sandbox (open to all).** Docs (`.adoc`),
+  tutorial walkthroughs, wiki pages, `.well-known/` content, and spec
+  proposals.
+
+### Fork workflow
+
+External contributors use the standard **fork**-and-pull-request
+workflow: fork the repository, branch from `main`, run `just` `validate`
+locally (full Agda verify + kernel-guard), and open a PR. Maintainers
+(Perimeter 1) may commit directly to feature branches. Every PR must
+keep `All.agda` + `Smoke.agda` green under `--safe` `--without-K` and
+introduce no banned constructs (see the pre-merge checklist above).

.machine_readable/root-allow.txt

@@ -1,2 +1,3 @@
 .hypatia-ignore
 CLAUDE.md
+build/                     # build orchestration: guix.scm relocated here (canon 1.2.1 guix-primary template_ref = "build/")

GOVERNANCE.adoc

@@ -114,7 +114,7 @@ This repository adheres to hyperpolymath estate-wide policies:
 * **License**: MPL-2.0 for code, CC-BY-SA-4.0 for prose (per standards/LICENCE-POLICY.adoc)
 * **Code of Conduct**: Follows hyperpolymath CODE_OF_CONDUCT.md
 * **Security**: Follows hyperpolymath SECURITY.md
-* **Contributing**: Follows hyperpolymath CONTRIBUTING.adoc conventions
+* **Contributing**: Follows hyperpolymath .github/CONTRIBUTING.md conventions
 
 == Repository-Specific Conventions
 
@@ -148,7 +148,7 @@ Changes to this document require the same process as Significant Changes above.
 
 * link:MAINTAINERS.adoc[Maintainers]
 * link:CODE_OF_CONDUCT.md[Code of Conduct]
-* link:CONTRIBUTING.adoc[Contributing Guide]
+* link:.github/CONTRIBUTING.md[Contributing Guide]
 * link:https://github.com/hyperpolymath/standards/blob/main/LICENCE-POLICY.adoc[Estate License Policy]
 * link:https://github.com/hyperpolymath/standards[rhodium-standard-repositories (TPCF)]
 

guix.scm → build/guix.scm

@@ -1,6 +1,6 @@
 ;; SPDX-License-Identifier: MPL-2.0
 ;; Guix development environment.
-;; Usage: guix shell -D -f guix.scm
+;; Usage: guix shell -D -f build/guix.scm
 
 (use-modules (guix packages)
              (guix build-system gnu)