# Step: ProgramArgs + IOChan

Tag `v3-programargs-iochan`. Suite **126/126**; fixpoint **OK**
(`bootstrap/fixpoint.sh`, image **2,071,330 bytes**).

## `ProgramArgs`

- `ArgCount() : CARDINAL` — the number of arguments *after* the
  program name.
- `GetArg(n : CARDINAL; VAR s : ARRAY OF CHAR) : BOOLEAN` —
  1-based (`1` = first argument); `FALSE` when absent.
- Over `SysShim.argc`/`SysShim.arg` → shim `m2argc`/`m2arg`, which
  read `/proc/self/cmdline` (Linux).

## `IOChan`

- `TYPE ChanId;` — opaque; completed as `ADDRESS` (a C `FILE *`).
- `StdInChan`/`StdOutChan`/`StdErrChan`.
- `ReadChar`, `WriteChar`, `WriteString`, `WriteLn`, `WriteInt`.
- All operations go through `SysShim` (`stdin`/`stdout`/`stderr`,
  `fgetc`/`fputc`/`fputs`/`fwriteln`/`fwriteint`); a `NIL` handle
  degrades to a safe no-op / `0C`, as in `Files`.

## Bridge additions

- `runtime/syslib/SysShim.def`/`.mod`: `argc`, `stdin`, `fgetc`,
  `fwriteint`.
- `runtime/syslib/shim.c`: `m2stdin`.

## Tests

- `progargs_prog.mod` (exit 7, run with no arguments): `ArgCount = 0`,
  `GetArg(1)` and `GetArg(999)` return `FALSE`.
- `iochan_prog.mod`: writes `hello 42` on `StdOutChan`, reads one
  character from `StdInChan`, echoes `got Z`; first stdout line
  `hello 42`, exit 0.

## Scope notes

- `ProgramArgs.ArgCount` excludes `argv[0]`; `GetArg` is 1-based.
- `IOChan` is a pragmatic subset: `ReadString`, `ReadResult`,
  seek/position and channels over files are not included; `ChanId`
  wraps only the standard streams for now.

## Files

`stdlib/programargs.def`/`.mod`, `stdlib/iochan.def`/`.mod`,
`runtime/syslib/SysShim.def`/`.mod`, `runtime/syslib/shim.c`,
`compiler/tests/{progargs_prog,iochan_prog}.mod`,
`compiler/run_tests.sh`, `docs/{features,plan}.md`.