diff --git a/docs/JOURNAL.md b/docs/JOURNAL.md
index b5928de..8e6c11b 100644
--- a/docs/JOURNAL.md
+++ b/docs/JOURNAL.md
@@ -12652,3 +12652,110 @@ content-not-grep issue caught by quality review). The Sweep 1
 lesson held. One plan-vs-actual phrasing variance ("a later iter"
 vs "a future iteration") was caught by the implementer at edit
 time and applied correctly without a fixup.
+
+## 2026-05-10 — Iteration design-md-consolidation 3: schema SoT inversion + data-model hardening
+
+Third iteration of the milestone defined in
+`docs/specs/2026-05-10-design-md-consolidation.md`. Sweep 3
+inverts the schema source-of-truth between `docs/DESIGN.md`
+§"Data model" and `crates/ailang-core/src/ast.rs`: DESIGN.md is
+canonical, `ast.rs` is the projection, and a new drift test
+catches divergence.
+
+Three substantive changes plus one new test:
+
+- **Two Rust code blocks removed from Decision 10.** The
+  `Type::Fn` + `ParamMode` block (around line 1027 at iter
+  start) and the `Suppress` struct block (around line 1132) are
+  replaced by prose pointers to §"Data model". Decision 10's
+  prose argument (per-position metadata vs `Type::Borrow`
+  variant) reads cleanly without the inline Rust.
+- **§"Data model" SoT inversion.** The opener now reads "**This
+  section is the canonical schema.**" The Rust types in `ast.rs`
+  are framed as the in-memory projection, not the source. The
+  drift test is named as the enforcement mechanism in the
+  opener.
+- **`ast.rs` module doc-comment.** The file-level `//!` block
+  bold-emphasises that DESIGN.md §"Data model" is canonical;
+  names the drift test as the enforcement; preserves the
+  serde-attribute description and the entry-type pointer.
+- **`crates/ailang-core/tests/design_schema_drift.rs`** is the
+  new drift test (369 lines). Pattern follows the existing
+  `spec_drift.rs`: exhaustive `match` per enum (`Term`,
+  `Pattern`, `Type`, `Def`, `Literal`, `ParamMode`) ensures
+  adding a variant without a DESIGN.md anchor fails compilation;
+  the test asserts each anchor literally appears in DESIGN.md.
+  7 tests total. All GREEN on first run after the schema-tag
+  alignment described below.
+
+**Real schema-vs-doc drift surfaced and closed inside the iter.**
+The drift test exposed a pre-existing bug: `ast.rs`'s `Def` enum
+uses `#[serde(tag = "kind", rename_all = "lowercase")]`, so
+shipped `.ail.json` examples emit `"kind": "class"` /
+`"kind": "instance"`. But Decision 11 §"Form-A schema" in
+DESIGN.md said `"kind": "ClassDef"` / `"kind": "InstanceDef"`.
+Confirmed by grepping `examples/test_22b1_*.ail.json` — every
+shipped example uses lowercase tags, matching the serde output.
+Per Sweep 3's commitment ("DESIGN.md is the canonical schema"),
+DESIGN.md was wrong; closed with fixup `934a6e1`: Decision 11
+JSON code blocks now use lowercase tags, drift test anchors
+updated to match. Prose references to the Rust type names
+`ClassDef` / `InstanceDef` (e.g. line 1382's
+"`**ClassDef**` — top-level definition kind, declares a class:")
+are fine — those reference the Rust struct names, not the JSON
+tag values.
+
+Quality-review nit closed inline: the test's file-level
+doc-comment originally opened with `Sweep 3 / Task 4:` (a
+task-reference prefix per CLAUDE.md comment policy is noise
+once the iteration is closed). Doc-comment trimmed; def-kind
+description list updated from PascalCase
+(`ClassDef`/`InstanceDef`) to lowercase (`class`/`instance`)
+to match the post-fixup anchors.
+
+Acceptance:
+
+- `grep -nE '^\s*(struct |enum |pub (struct|enum|fn))' docs/DESIGN.md` → empty.
+- `grep -n 'whenever the two disagree\|ast.rs is the source of truth' docs/DESIGN.md` → empty.
+- `grep -n 'This section is the canonical schema' docs/DESIGN.md` → 1 line (1708).
+- `grep -n 'design_schema_drift' docs/DESIGN.md crates/ailang-core/src/ast.rs` → 1 match in each file.
+- `cargo test -p ailang-core --test design_schema_drift` → 7 tests pass.
+- `cargo test --workspace` → 0 FAILED.
+- `bench/check.py` 0 regressed (63 metrics; 3 improved beyond
+  tolerance, 60 stable). `bench/compile_check.py` 0 regressed
+  (24 metrics, 24 stable).
+- Sweep-1 + Sweep-2 invariants stay empty (no regression).
+- DESIGN.md size: 2155 → 2139 lines (−16 this sweep, −123
+  cumulatively from 2262 at milestone start).
+
+Tasks (commit subjects):
+
+- design-md-consolidation 3.1: remove 2 Rust code blocks from Decision 10
+- design-md-consolidation 3.2: invert §Data-model SoT — DESIGN.md canonical, ast.rs projection, drift test enforces
+- design-md-consolidation 3.3: ast.rs doc-comment names DESIGN.md §Data-model as canonical schema, drift test as enforcement
+- design-md-consolidation 3.4: add design_schema_drift.rs — exhaustive-match drift test for ast.rs vs DESIGN.md §Data-model
+- design-md-consolidation 3.4 fixup: align DESIGN.md ClassDef/InstanceDef JSON tags with ast.rs lowercase serde rename
+- design-md-consolidation 3.4 nit: drop task-ref doc-comment prefix + align def-kind list with lowercase tags
+
+Carried into sweep 4: workflow / cross-reference cleanup.
+"Project ecosystem" `agents/` path correction; "Verification and
+correctness" workflow detail; "What is not (yet) supported"
+§"Recently lifted gates" removal; cross-reference audit.
+
+Process notes:
+- The plan predicted "GREEN on first run — DESIGN.md already
+  aligned" for the drift test. Reality matched in the sense
+  that the test's grep-presence checks all passed on first run
+  — but the schema-vs-emit drift between DESIGN.md and ast.rs
+  was a different bug class that the grep-presence test wasn't
+  designed to catch. Surfacing happened anyway because the
+  implementer flagged it as known debt; the orchestrator
+  promoted it to in-scope and closed it.
+- Open question for follow-up sweeps: the current drift test
+  guards DESIGN.md text presence, not serde-roundtrip fidelity.
+  A future hardening would round-trip a constructed `Def` value
+  through `serde_json::to_value` and assert the emitted JSON
+  matches one of DESIGN.md's anchors literally — that catches
+  the ClassDef/class class of bug structurally rather than
+  through grep-presence + spot inspection. Out of scope for
+  iter 3; queued.
diff --git a/docs/roadmap.md b/docs/roadmap.md
index c5dec2f..c371b73 100644
--- a/docs/roadmap.md
+++ b/docs/roadmap.md
@@ -41,7 +41,7 @@ work progresses.
   - sub-entries:
     - [x] Sweep 1 — remove history anchors
     - [x] Sweep 2 — REVERTED + migration plans out
-    - [ ] Sweep 3 — schema SoT inversion + data-model hardening
+    - [x] Sweep 3 — schema SoT inversion + data-model hardening
     - [ ] Sweep 4 — workflow / cross-reference cleanup
 
 ## P1 — Next