Phase 1: real codegen — layout engine + typed-access lowering (#146)

Real codegen, replacing representative stub bodies, harvested from the Zig twasmc reference (PR #136, closed superseded with credit):
- layout engine (field offsets, element stride, alignment, inline embedded regions — Players slot 48B, nested .pos.x into @vec2 at offset 16)
- typed-access lowering (Body::Typed/Stmt/Access): real loads/stores at base + index*stride (+ offsets), via a base-pointer local read once per handle (keeps &mut/own clean under the verifier)
- example 01 now carries &/&mut ownership; example 03 reads via base locals

ADR-0004 ratified (Proposed -> Accepted) recording the Rust-vs-Zig decision + harvest; CHANGELOG + crate README updated. Verified locally (cargo test --workspace --locked: codegen 22 + verifier 80; fmt + clippy clean; no new deps) since Actions credit is exhausted. Closes the representative-bodies gap from #127 (front-end -> IR seam still deferred). Part of Phase 1 (#49).

https://claude.ai/code/session_01Rq4da8i2uGnDUfanSB1Hx4

Author: hyperpolymath

CHANGELOG.md

@@ -22,6 +22,23 @@ self-verifies in-process — by verifying a `.wasm` from **any** producer,
 including external / third-party modules. Validated against `tw build`
 output (`structural ✓ · L7/L10/L13 ✓ · L2 ✓`).
 
+### Real codegen: layout engine + typed-access lowering, harvested from Zig `twasmc` (#136) (2026-05-30)
+
+The Rust producer's function bodies are now **real codegen**, not representative
+stubs. A layout engine computes field offsets, element strides, and alignment —
+including inline embedded regions (`Players` slot stride 48 B; `.pos.x` reaches
+into the embedded `@Vec2` at offset 16) — and typed accesses emit real
+loads/stores at computed offsets addressed as `base + index*stride (+ offsets)`.
+Each region handle is read once into a base-pointer local, so `&mut`/`own` params
+stay clean under the verifier; example 01 now also carries `&`/`&mut` ownership.
+
+After a head-to-head Rust-vs-Zig comparison, the host-language choice was
+ratified (**ADR-0004 → Accepted**) and the approach + base-local convention were
+harvested from the parallel Zig producer (`twasmc`, PR #136), which was closed as
+superseded with credit. Closes the representative-bodies gap noted in #127; the
+front-end → IR parser seam remains (#127) and `if`/`region.scan` control flow is
+still simplified.
+
 ### In-tree producer: `typed-wasm-codegen` (codegen v0 → multi-module, debug info, human errors) (2026-05-30)
 
 Adds the first in-tree `.twasm` → `.wasm` **producer** as a Rust crate
@@ -51,9 +68,10 @@ boundary, all verifier-backed. Deferred (tracked): the front-end → IR seam +
 remaining examples (#127), source → line maps (#129), region-imports /
 L13-positive (#140), ECHIDNA round-trip corpus (#130).
 
-> Note: an alternative **Zig** producer (`twasmc`, `src/codegen/`) was
-> proposed in parallel in PR #136 (draft, open). Host-language reconciliation
-> against ADR-0004 (Rust) is an open owner decision.
+> Note: an alternative **Zig** producer (`twasmc`, `src/codegen/`) was proposed
+> in parallel in PR #136; after a Rust-vs-Zig comparison the Rust track was
+> retained (ADR-0004 **Accepted**) and #136 was closed as superseded, its layout
+> approach harvested — see the "Real codegen" entry above.
 
 ### Multi-producer carrier ABI: proposals 0001 + 0002 accepted, promoted to ADRs (2026-05-30)
 

crates/typed-wasm-codegen/README.md

@@ -12,8 +12,9 @@ seeds Phase 1 (issue #49, deliverable 1).
 
 Lowers a typed region IR ([`Module`](src/lib.rs)) to:
 
-- a **well-formed wasm module** (linear memory + type-correct function
-  bodies), and
+- a **well-formed wasm module** with **real typed loads/stores at
+  layout-computed offsets** (element `base + index*stride`, nested `.pos.x`
+  into inline embedded regions), and
 - the L2–L6 carrier sections **`typedwasm.regions`** (ADR-0002) and
   **`typedwasm.access-sites`** (ADR-0003),
 
@@ -57,7 +58,7 @@ cargo test -p typed-wasm-codegen
 | `typedwasm.ownership` (L7/L10) | **emitted** — Linear/ExclBorrow/SharedBorrow (example 03 + multi-module callee), checked by `verify_from_module` |
 | Multi-module (linear boundary) | **emitted** — callee export + caller import round-trip through `verify_cross_module` (#128) |
 | Debug symbols (`name` section) | **emitted** — function names for debuggers (#129, first increment) |
-| Function-body lowering | representative type-correct bodies, not full `region.scan`/indexing semantics |
+| Function-body lowering | **real** — layout engine (offsets/stride/align, inline embedded regions) + typed loads/stores via a base-local (harvested from Zig `twasmc` #136); `if`/`region.scan` control flow still simplified |
 
 ## Example coverage (#127)