# Two-phase refactor — slice 7 (unit root + builtin statements)

Branch `ast-stage-c`.  Suite **178/178**; self-hosting fixpoint **OK**
(**3,016,802 bytes**; slice 6 was 3,007,851).

## What landed

### Unit root

A module-level `astUnit` now holds `NkUnit(name, decls, body)` for
DEFINITION, IMPLEMENTATION and program modules.  `decls` is the unit's
`NkDeclSeq` (from `DeclSeq`) and `body` is the program/init `NkBlock`
(or `NoNode`).  `ProgModule` and `ImplUnit` also reset `astStmt`/
`astDecl` at entry, so the root never picks up a stale node.

### Builtin statements

`INCL`/`EXCL`, `INC`/`DEC`, `NEW` and `DISPOSE` now build `NkCall`s
whose callee is an `NkIdent` naming the builtin, with the designator
(and step/element expression) as children.  Node-building is inserted as
extra actions around the existing emit actions, which are unchanged.

## Verified (temporary `AST.Dump` of `astUnit`, then removed)

```modula2
VAR x : INTEGER; s : BITSET; p : POINTER TO INTEGER;
BEGIN
  INC(x); INCL(s, 1); NEW(p); DISPOSE(p)
END
```

produced

`NkUnit(Ident unitdump, NkDeclSeq[NkVarDecl x/s/p], NkBlock[
  NkCall(INC, x), NkCall(INCL, s, 1), NkCall(NEW, p), NkCall(DISPOSE, p) ])`

with each `NkVarDecl` carrying its `ty` index.

## Deliberately deferred

- Imports (`NkImport`), `CLASS` items, nested modules in the unit AST.
- `CASE` and `WITH` statements.
- Brace/set literals and `ResultComp` call suffixes.
- `Lower` + `.ssa` byte-compare.

## Next

`CASE`/`WITH`; imports/`CLASS`; brace/set literals; then the `Lower`
walk.