diff --git a/.ciagent/CHECKPOINT.json b/.ciagent/CHECKPOINT.json
index fb950c1..108383b 100644
--- a/.ciagent/CHECKPOINT.json
+++ b/.ciagent/CHECKPOINT.json
@@ -1,11 +1,11 @@
 {
   "phase": 0,
-  "stage": "plan",
+  "stage": "mvp_ux_check",
   "milestone": "v0.4",
   "milestone_type": "nfr",
   "tag_base": "v0.3.x",
   "phase_role": "pre_execution",
   "project": "oy",
   "attempts": 0,
-  "updated_at": "2026-08-17T22:48:00Z"
+  "updated_at": "2026-08-17T22:50:00Z"
 }
\ No newline at end of file
diff --git a/.ciagent/oy/PLANS.md b/.ciagent/oy/PLANS.md
index 4c2bf06..8df6a07 100644
--- a/.ciagent/oy/PLANS.md
+++ b/.ciagent/oy/PLANS.md
@@ -996,4 +996,51 @@ None. P1, P2, P3 are independent vertical slices. P4 depends on P1+P2+P3 complet
 | D-050 | REQ-031 = document only, no feat: enum additions | P2-01-01, P2-02-01 |
 | D-051 | REQ-032 docs CI = .gitea/workflows build+artifact, no Pages | P3-01-01 |
 | D-052 | Phase ordering P1→P2→P3→P4 | Phase ordering |
-| D-053 | No IDEATE in v0.4 (no --ideate flag) | (no IDEATE stage run) |
\ No newline at end of file
+| D-053 | No IDEATE in v0.4 (no --ideate flag) | (no IDEATE stage run) |
+
+---
+
+## MVP/UX Check (REQ-MVP-UX-001) — v0.4 NFR Milestone
+
+> Auto-generated at full autonomy per run.md §MVP/UX CHECK. The three required
+> sections below name at least one user-facing surface, a happy path written
+> BEFORE execute, and explicit UX acceptance criteria. v0.4 is an NFR milestone,
+> so "user-facing surface" is developer-facing (the lexicon firewall, the
+> cross-const test, the CI workflow) and the docs site build (end-user-facing
+> via the published docs artifact).
+
+### User-Facing Surface
+
+1. **Lexicon firewall (developer-facing)**: `go test ./lexicon_meta... ./lexicon_meta_docs/...` — the green test output is the surface a developer sees on every `go test ./...` run. After REQ-029, both meta-tests consume `lexicon.SyntheticBannedStrings()`; a future banned-term addition updates both firewalls from one place.
+2. **Cross-const drift test (developer-facing)**: `go test ./x/hub/types/...` — `TestConstsAreMissionLocked800And0` is the surface a developer sees if the hub↔bond mission-locked consts ever drift.
+3. **Docs build CI (end-user-facing via artifact)**: `.gitea/workflows/docs-build.yml` produces a `site/` artifact on every push. A maintainer downloads the artifact to preview the docs site without running `mkdocs build` locally.
+4. **ARCHITECTURE.md divergence section (developer-facing)**: a contributor reading `.ciagent/oy/ARCHITECTURE.md` finds the "Council Voice/Council Interface — Lifecycle Type Divergence Decisions (v0.4)" subsection explaining why `SignalKind` is 4-not-5 and why `Proposal`/`VoteOption` are absent.
+
+### Happy Path
+
+**Scenario: a contributor adds an 11th banned term to the lexicon firewall.**
+
+1. The contributor edits `lexicon/lexicon.go` to add a new fragment pair to `fragments` (e.g., a new banned term).
+2. `lexicon.BannedTerms()` now returns 11 strings.
+3. `lexicon.SyntheticBannedStrings()` (REQ-029) is the single source — the contributor does NOT need to update two meta-test tables (the v0.3 drift risk).
+4. `go test ./lexicon_meta... ./lexicon_meta_docs/...` — both meta-tests consume the helper; the `len(terms) == 10` assertion in BOTH meta-tests now fails (expecting 11), alerting the contributor to update the count assertion in both files.
+5. The contributor updates the `len(terms) == 11` assertion in both meta-tests (the G-014 minimum — both already derive count from `BannedTerms()`).
+6. Both meta-tests pass; the new banned term is now enforced in BOTH the `x/**/*.go` firewall AND the `docs/**/*.md` firewall from one source change.
+7. The contributor pushes; `.gitea/workflows/docs-build.yml` (REQ-032) runs `go-test` (green) → `docs-build` (green, G-016 gating) → `site/` artifact uploaded.
+
+**Scenario: a contributor accidentally changes `x/bond.CouponCapBps` from 800 to 900 without updating `x/hub.LendingCouponCapBps`.**
+
+1. `go test ./x/hub/types/...` — `TestLendingCouponCapMatchesBondCap` (REQ-030) fails: `hub.LendingCouponCapBps (800) != bond.CouponCapBps (900)`.
+2. `TestConstsAreMissionLocked800And0` (G-015) ALSO fails: `bond.CouponCapBps (900) != 800`.
+3. The contributor sees two failures pointing at the same root cause; the mission-locked 8% cap is defended by the cross-const test. The v0.3 A-304 drift risk is closed.
+
+### UX Acceptance Criteria
+
+The v0.4 deliverable MUST meet these explicit criteria (verified in P4 audit):
+
+1. **REQ-029**: `lexicon.SyntheticBannedStrings()` exists; both `lexicon_meta_test.go` and `lexicon_meta_docs/lexicon_meta_docs_test.go` consume it; the duplicated 10-string table is gone (grep for the old literal sentence fragments returns zero matches in meta-test files).
+2. **REQ-030**: `x/hub/types/cross_const_test.go` exists; `TestLendingCouponCapMatchesBondCap`, `TestLendingCouponFloorMatchesBondFloor`, and `TestConstsAreMissionLocked800And0` all pass (G-015); no production `.go` file in `x/hub/types/` imports `x/bond/types` (G-003 production firewall intact).
+3. **REQ-031**: ARCHITECTURE.md has the Council lifecycle divergence subsection; `TestSignalKindShapeIntentional` in `x/council/types/types_test.go` passes and documents the 4-signal rationale; `SignalKindCount` unchanged (still 4); no production `.go` files modified in P2.
+4. **REQ-032**: `.gitea/workflows/docs-build.yml` parses; runs `go test ./...` then `mkdocs build` (G-016: `docs-build` needs `go-test`); `go.mod` unchanged.
+5. **NFR purity gate**: zero `feat:` commits in the v0.4 milestone range (P4 audit enforces).
+6. **No regression**: `go test ./...` green; v0.3 coverage floor (93.3%) not reduced on any modified package.
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