# Two-phase refactor — slice 12 (nested modules)

Branch `ast-stage-c`.  Suite **178/178**; self-hosting fixpoint **OK**
(**3,034,200 bytes**; slice 11 was 3,032,308).

## What landed

`NestedModule` now builds an `NkUnit(name, decls, body, imports)` using
its own local import accumulator (`nImp`/`nImpTail`), and sets `astDecl`
to that node — so the enclosing `DeclSeq` records the nested module as a
declaration.  A local accumulator keeps the enclosing unit's imports
(`astImp`) intact.

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

```modula2
MODULE nestdump;
VAR x : INTEGER;
MODULE Inner;
  VAR y : INTEGER;
BEGIN y := 5 END Inner;
BEGIN x := 1 END nestdump.
```

gave the outer `NkUnit(nestdump, decls=[NkVarDecl x, NkUnit(Inner,
decls=[NkVarDecl y], body=[y:=5])], body=[x:=1])`.

## Still not covered

- **`CLASS` / `CLASS IMPLEMENTATION`** items.  Note: the compiler's own
  sources contain **no** actual class declarations (only the word in
  comments and the scanner's keyword table), so this is not needed for
  self-hosting validation — it is a user-facing OOP feature and a
  sizeable slice of its own.
- `Lower` + `.ssa` byte-compare.
- `MaxChild` cap on `CASE` arms / `WITH` designators / call actuals.

## Next

`CLASS` (if desired) or the `Lower` walk.