From 4ab6d452da7f9d2f3e68e7b6fb7c646ece48bd69 Mon Sep 17 00:00:00 2001
From: hyperpolymath <6759885+hyperpolymath@users.noreply.github.com>
Date: Sun, 31 May 2026 00:29:01 +0100
Subject: [PATCH] =?UTF-8?q?docs(vision):=20add=20`=3D=3D=20The=20Dyad=20an?=
 =?UTF-8?q?d=20the=20Layers`=20per=20PRESERVATION-DESIGN=20=C2=A712.4?=
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Executes `formal/PRESERVATION-DESIGN.md` §12.4 (EPHAPAX-VISION
rollout):

Insert a new section between `== The Dyad` and
`== One Language, One Feel` titled `== The Dyad and the Layers`.

The new section extends — does not replace — the dyad framing. Per
the spec's §12.4 instruction:

> The vision doc already articulates the dyad beautifully [...].
> The four-layer story *extends* this; it does not replace it.

The new section maps each layer (L1 / L2 / L3 / L4) onto what the
dyad says about it:

- L1 (regions) — identical in both modes; same soundness story.
- L2 (modality) — the dyad itself; `linear_to_affine` mechanises
  Linear ⊆ Affine.
- L3 (echo) — mother demands the residue be observed; child may
  silently lower.
- L4 (dyadic interaction) — declaration of which side you speak
  from.

Closes with: "The dyad remains primary. The layers are how the
dyad's promises are *enforced*."

No proof, code, workflow, or schema changes. Pure documentation
rollout. Companion to README #256 (§12.2) and EXPLAINME #257
(§12.3).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 docs/vision/EPHAPAX-VISION.adoc | 49 +++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/docs/vision/EPHAPAX-VISION.adoc b/docs/vision/EPHAPAX-VISION.adoc
index b804c9f..2ca6097 100644
--- a/docs/vision/EPHAPAX-VISION.adoc
+++ b/docs/vision/EPHAPAX-VISION.adoc
@@ -94,6 +94,55 @@ linear" or "linear in training." It has intrinsic value. There are programs
 that belong in affine permanently. As Ephapax matures, the affine form must
 mature *into itself* — not toward becoming linear.
 
+== The Dyad and the Layers
+
+The dyad — linear mother, affine child — is one of *four orthogonal
+disciplines* that together define Ephapax. The other three are silent
+partners in the dyad: each is enforced independently, but each takes its
+*defaults* from which side of the dyad you are on.
+
+[cols="1,3", options="header"]
+|===
+| Layer | What the dyad says about it
+
+| L1 — Region capabilities
+| Identical in both modes. Every live region is tracked in an
+  input/output capability environment threaded through every
+  compound expression. A sibling cannot reference a region a
+  previous sibling has exited. The mother and the child obey the
+  same L1 invariant; the soundness story is the same.
+
+| L2 — Structural modality
+| *This is the dyad itself.* The mother is `Linear`; the child is
+  `Affine`. The thin-poset embedding `Linear ⊆ Affine` is
+  mechanised as `linear_to_affine : Linear ≤ Affine` (Qed, zero
+  axioms in `formal/Modality.v`). Every Linear derivation is an
+  Affine derivation; not every Affine derivation is Linear.
+
+| L3 — Irreversibility residue (Echo)
+| The discipline of *what was lost*. When a region exits or a
+  binding drops, the value is gone — L3 captures the residue as
+  a typed witness. The mother demands the residue be observed
+  (no silent discarding); the child may silently lower it. The
+  same `Echo` fiber serves both modes; only the rule for
+  consuming it differs.
+
+| L4 — Dyadic interaction
+| The declaration of which side you speak from. The mother answers
+  to the linear discipline; the child to the affine. Every closed
+  program has one.
+|===
+
+The four layers compose without coherence obligations because each
+is a *thin poset* — propositional ordering kills the categorical
+overhead that would otherwise demand pentagon laws and the like. The
+construction is taken verbatim from
+https://github.com/hyperpolymath/echo-types[echo-types]'
+decoration-commuting recipe.
+
+The dyad remains primary. The layers are how the dyad's promises
+are *enforced*.
+
 == One Language, One Feel
 
 Writing in Ephapax Linear and Ephapax Affine feels *identical*. There are no