# Step 6 — Local modules hardened (uncommitted)

112/112 tests green (99 regressions + 5 run + 8 rejection), mc64 boot + example green.

## Goal

Harden the step-6 WIP (single-file local `MODULE`s, no nesting, no bodies):
exported `VAR`s, `CONST`s and parameterless proper procedures, used as
`M.x` / `M.P()`. Fix the bugs found by probing, lock behavior in with
rejection tests, keep every old suite green.

## What was built

- `SymTab`: `ExpQual` now qualifies `KindConst` as well as `KindVar`
  (`"M.x"`); `ExitModule` became a `BOOLEAN` function — `TRUE` iff every
  `EXPORT` name was declared (ghost exports report `FALSE`).
- `M2c.atg`: `ModuleDecl` gained an `enterOk` flag (failed `EnterModule`
  skips export recording and `ExitModule`, killing the duplicate-module
  cascade); `END` reports `SemError(201)` on ghost exports; header comment
  documents local-module support and limits.
- `run_tests.sh`: new `Step-6` sections (5 run + 8 rejection).

## Tests — 112/112 (99 + 5 + 8)

5 run: `m_mod` 12 (exported var + `Inc()` twice), `m_multi` 7 (two
modules), `m_arr` 42 (exported array + `M.arr[2]`), `m_outer` 11 (module
proc touches outer global), `m_const` 7 (exported `CONST`).
8 rejections, each exactly one error: `m_bad_priv` 201 (private `M.secret`),
`m_bad_nest` 230 (module in procedure), `m_bad_dup` 200 (duplicate module),
`m_bad_exp` 200 (duplicate export), `m_bad_ghost` 201 (`EXPORT ghost`),
`m_bad_param` 233 (`M.Add(5)`), `m_bad_func` 233 (`M.Get()` in expression),
`m_bad_end` 202 (`END N` mismatch).

## Bugs found and fixed

1. Exported `CONST` read back 0: `ExpQual` returned an empty name for
   non-`Var` kinds, so `GlobalAddr("")` hit a temp slot. Qualifying
   `KindConst` fixes the load (`M.C` → 7) with no ATG change (address +
   `LoadIndir` path is shared with vars).
2. Ghost `EXPORT` silently accepted: `ExitModule` dropped undeclared names.
   Now returns `FALSE` and the ATG reports 201 at `END`.
3. Duplicate module gave 2 errors (200 at name + 200 at its `EXPORT`, since
   `ModuleAddExp` ran with no module context). `enterOk` guard → 1 error.

## Known limits (each with a rejection test or documented)

Module procedures take no parameters (`M.Add(5)` → 233), module functions
are statement-only (`M.Get()` in an expression → 233), no type exports
(`M.T` → 221 + 230 via `QualIdent`), no `DEFINITION`/`IMPLEMENTATION`
split, no module `BEGIN` bodies, `NoteSfx`/`NoteIdx` VAR-tail helpers still
unwired (`a[i]`/`p^`/fields as VAR actuals → 233), max 8 modules /
32 exports per module / 128 exports total.

## Text output (I/O builtins, verified this session)

No new machinery needed for simple output — step-5 builtins cover it:
`WriteString("...")` / `WriteString(charArrayVar)` emits raw bytes via
SYSTEM service 1 (no newline); `WriteInt(n)` emits unsigned decimal + CRLF
via the embedded `EmitPrint` helper; a declared `ExitCode` global is printed
the same way at program end. Demo verified under `mcint`:
`WriteString("Hello"); WriteString(" world"); WriteInt(42);`
→ `Hello world42\r\n`. Limits: no `WriteLn`, single-`CHAR` literals rejected
(210 — `"A"` lexes as `CHAR`, not a string), `WriteInt` wraps negatives, one
value per call. A `WriteLn`/`WriteChar` would be a small isolated addition
(new ATG builtin + `MGen` emitter + tests).