# Handoff — L3 via option 2: 183/183 but self-host blocked by V3 codegen

Branch **`ast-stage-c`**, HEAD **`edf24d9`**.  Suite **182/182**;
fixpoint **OK** (**3,147,849 bytes**).  Clean except `toto.mod`.

## Headline

Option 2 (zero `SymTab` surface) is **functionally complete** and
**byte-verified**: `t_lower3` matches the legacy image and the suite
reaches **183/183** with `lower_ok t_lower3`.  It **still does not
self-host**, and the cause is now a *different* V3 codegen bug, not the
table design.

## What was built and verified this session

`compiler/src/Lower.def` / `Lower.mod`:

- Owned, **flat** tables (no arrays of records — see the bug below):
  `symName : ARRAY OF CHAR` (stride 64), `symKind`, `symTy`, and
  `procs : ARRAY OF ProcEnt` with a flat `pname` (stride 64).  Helpers
  `Reset`, `NoteVar`, `NoteParam`, `NoteProc`, `SetProcRes`,
  no-op `ScopeEnter`/`ScopeLeave`, `CopyN`/`CopySpan`, `FindSym`/
  `FindProc`/`Resolve`/`ProcInfo`/`ParamInfo`.  **No `SymTab` edits.**
- All `SymTab.ProcUid/ProcNPar/ParamType/...` call-sites switched to
  `ProcInfo`/`ParamInfo`; `LowerDesign`/`IsSimpleScalar`/`IsCall` to
  `Resolve`/`FindProc`.
- Grammar hooks (inert): `M2` root `Lower.Reset`; `VarDecl`/`ConstDecl`
  `Lower.NoteVar`; `ProcHeading` `Lower.ScopeEnter`+`NoteProc`+
  `SetProcRes`; `ParamSection` `Lower.NoteParam`/`NoteVar`; `ProcDecl`
  `Lower.ScopeLeave` + `AST.SetOp(astNode, 0)`.
- `ScopeLeave` is a **no-op**: parse-time notes must survive until the
  end-of-unit walk.

Result: `t_lower3` (function + VAR-param procedure + calls + RETURN)
**byte-matches**; suite **183/183**.

## New finding — nested-array record field miscompiles

Repro `docs/wip/nested-array-field-bug.mod`:

```modula2
TYPE PE = RECORD
  name  : ARRAY [0..63] OF CHAR;
  pname : ARRAY [0..3] OF ARRAY [0..63] OF CHAR;   (* nested *)
END;
VAR procs : ARRAY [0..3] OF PE;
...
procs[nProcs-1].pname[j][i] := name[i];
```

`./M2` compiles it, but the **generated program segfaults** (rc 139;
want 42).  A **flat** `pname : ARRAY [0..2047] OF CHAR` (manual stride)
works.  This is a real user-facing bug — likely the element stride /
descriptor-pointer setup for a nested-array field (same family as the
Stage-A array-of-record stride fix in `QbeGen.ElemSize`, and
`docs/wip/local-array-bug.mod`).

It was hit directly: the V3-built compiler (`m2s2`) crashed on **every**
input when `Lower`'s formal-name table used a nested-array field.
Flattening fixed that crash.

## Why self-host still fails

After flattening, `m2s2` works on small programs (`t_exit`, a `CONST`
program) but **still crashes (SIGABRT) on the full compiler input**
(empty output).  Shrinking the tables (`MaxSym` 2048→512, `MaxProc`
512→64) did **not** help, so it is not table size — it is a
**size/complexity-triggered latent V3 codegen bug** in the compiled
`Lower`/`M2P` code.  HEAD self-hosts; the ~250 added lines tip it over.

This is the third instance of the same compiler fragility (local arrays,
nested-array fields, and now this).  Finding the exact construct needs a
bisect of the added code with a V3-built compiler — a dedicated task.

## Next steps

1. **Fix the nested-array-field bug in `QbeGen`** (like the Stage-A
   stride fix): make `arr[i].field[j][k]` correct.  Add the repro to the
   suite.  This is a real, self-contained bug and may also matter for the
   size-triggered failure.
2. **Bisect the size-triggered self-host crash**: build `m2s2`, then
   compile subsets of the added `Lower`/`M2P` code with it to find the
   construct that crashes.  Candidates: the flat-stride indexing, the
   `CopySpan` offsets, or a specific grammar hook.
3. Once self-host is green: keep `lower_ok t_lower3`, expect 183/183 +
   FIXPOINT OK.

## Do NOT

- No `FORWARD` (breaks gm2 whole-program pass).
- No `SymTab` edits.
- No arrays of records with aggregate (nested-array) fields in `Lower`.
- No committed `ASTDUMP`.

## Resume

```sh
cd ~/Projets/Projets-Modula2/MyWork/m2compiler-V3
git checkout ast-stage-c
cd compiler && ./build.sh && ./run_tests.sh   # 182/182
cd .. && ./bootstrap/fixpoint.sh              # FIXPOINT OK
```