# Lower phase — L6 status (2026-10-05)

Branch **`ast-stage-c`**.  L6 = "classes/vtables, imports, nested modules".

## Landed

**Nested modules** (`f82f72b`, tag `v3-lower6-nested`)
- `CanDecl` accepts a nested `NkUnit` (with no imports).
- `LowerDecls` emits the nested unit's declarations and, when it has a
  `BEGIN` body, `BeginInit`/body/`EndInit` (registering `<nested>_init`
  so the enclosing `BeginBody` calls it).
- `ReenterGlobals` re-registers a nested module's non-exported globals in
  the still-open enclosing module scope, so `QbeGen.GlobalRef` resolves
  their `"<outer>_<name>"` symbols after the nested scope has been popped.
- `lower_ok t_nestedmod.mod` byte-matches.  Suite 194/194; FIXPOINT OK
  (3,328,857 bytes).

## Blocked / remaining

### Imports — blocked by the session-image model
`-lower` is invoked only from `ProgModule`'s END (`M2.atg`), so Lower
re-emits **only the last unit**.  But a session's image is accumulated
across all units (`sessBuf`): a program that `IMPORT`s a module pulls
that module's procs/init/globals into the *same* `gen_ssa/<Prog>.ssa`.
So re-emitting just the program cannot byte-match.

Supporting imports therefore needs a **mechanism change**: lower *every*
unit (definition/implementation/program) and accumulate a session image
(mirroring `sessBuf`), or otherwise compare per unit.  That is the same
mechanism the **L7 flip** needs, so it is the natural next structural
step.  Qualified names (`M.x`) additionally need `SymTab.MaterializeAlias`
at lowering time (module scope is open — workable) and qualified-call
resolution in `LowerCall` (currently `CalleeName` reads only the base
ident).

### Classes/vtables — large, single-unit, verifiable
Surface: `NkClassDecl`/`NkFieldDecl`, `CLASS IMPLEMENTATION`, method
binding (`obj.Method` + `ArmRecv`), virtual dispatch, inheritance, `NEW`
for classes, vtables (`QbeGen.EmitVTables`), `THIS`.  Independent of
imports, so it can be byte-verified with `lower_ok` on a self-contained
class program.

## Suggested order
1. Classes/vtables (verifiable now).
2. The per-unit lowering mechanism (unblocks imports and is the L7
   prerequisite).