divergence register -> docs/architecture (living doc) + CLAUDE.md rules: same-commit row discipline, symptom-scan trigger, phase-checklist hook

CLAUDE.md

@@ -457,6 +457,28 @@ isn't enough, attach cdb to a live retail client (Step -1).**
    source was safe; replacing the entire transform composition broke
    everything.
 
+### The divergence register (mandatory bookkeeping)
+
+[`docs/architecture/retail-divergence-register.md`](docs/architecture/retail-divergence-register.md)
+is the single auditable list of every KNOWN place acdream's runtime
+behavior can deviate from retail (108 rows at creation, 2026-06-12:
+intentional architecture / adaptation / approximation / stopgap /
+unclear). Two rules, both binding on subagents too:
+
+1. **Any commit that introduces a deviation** (an adaptation, an
+   approximation, a stopgap, a "retail does X but we...") **adds its
+   register row IN THE SAME COMMIT.** Any commit that ports the retail
+   mechanism deletes the row in the same commit. A deviation found
+   without a row is a bug twice over.
+2. **Any unexplained visual/physics symptom → scan the register BEFORE
+   instrumenting.** The "Risk if assumption breaks" column is written as
+   the symptom you'd observe (the #119 vanishing staircase, the #112
+   transparent cottage, and the knife-edge flap all lived in rows of
+   this register's scope before they had names).
+
+The register holds one-line rows and pointers — detail lives at the
+cited `file:line` and in the digests, never in the register itself.
+
 ### What NOT to do:
 
 - **Do not guess** at AC-specific algorithms, formulas, constants, wire
@@ -491,6 +513,9 @@ Before marking any phase as done:
 - [ ] Every AC-specific algorithm has a decompiled reference cited in
       comments (named symbol + address from `named-retail/symbols.json`,
       OR function address + chunk file from older `decompiled/` chunks)
+- [ ] Every retail deviation this phase introduced has a row in
+      `docs/architecture/retail-divergence-register.md` (and every
+      deviation it retired had its row deleted)
 - [ ] Conformance tests exist for the critical paths
 - [ ] The code was cross-referenced against at least 2 reference repos
 - [ ] `dotnet build` green, `dotnet test` green