ocaml: phase 6 Sys module constants (+5 tests, 414 total)

os_type="SX", word_size=64, max_array_length, max_string_length,
executable_name="ocaml-on-sx", big_endian=false, unix=true,
win32=false, cygwin=false. Constants-only for now — argv/getenv_opt/
command would need host platform integration.

plans/ocaml-on-sx.md

@@ -264,6 +264,10 @@ SX CEK evaluator (both JS and OCaml hosts)
 - [~] `Hashtbl`: `create`, `add`, `find`, `find_opt`, `replace`, `mem`,
       `length`. Backed by a one-element list cell holding a SX dict;
       keys coerced to strings via `str` for polymorphic-key support.
+- [~] `Sys`: `os_type` (`"SX"`), `word_size`, `max_array_length`,
+      `max_string_length`, `executable_name`, `big_endian`, `unix`,
+      `win32`, `cygwin`. Constants only; `argv`/`getenv_opt`/`command`
+      pending (would need host platform integration).
 - [x] `String`: `length`, `get`, `sub`, `concat`, `uppercase_ascii`,
       `lowercase_ascii`, `starts_with`, `ends_with`, `contains`, `trim`,
       `split_on_char`, `replace_all`, `index_of`.
@@ -379,6 +383,10 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 6 — `Sys` module constants (+5 tests, 414 total).
+  os_type, word_size, max_array_length, max_string_length,
+  executable_name, big_endian, unix, win32, cygwin. Constants-only
+  for now; `argv`/`getenv_opt`/`command` need host platform integration.
 - 2026-05-08 Phase 5 — parse simple type sources in user type-defs
   (+3 tests, 409 total). `ocaml-hm-parse-type-src` recognises
   primitive type names, tyvars `'a`, and `T list`/`T option`-style