ocaml: phase 6 String/Char/Int/Float/Printf modules (+13 tests, 278 total)

Host primitives _string_length / _string_sub / _char_code / etc. exposed
in the base env (underscore-prefixed to avoid user clash). lib/ocaml/
runtime.sx wraps them into OCaml-syntax modules: String (length, get,
sub, concat, uppercase/lowercase_ascii, starts_with), Char (code, chr,
lowercase/uppercase_ascii), Int (to_string, of_string, abs, max, min),
Float.to_string, Printf stubs.

Also added print_string / print_endline / print_int IO builtins.

lib/ocaml/test.sh

@@ -672,6 +672,36 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 913)
 (eval "(ocaml-type-of \"not true\")")
 
+;; ── Phase 6 expanded: String / Char / Int / Float modules ─────
+(epoch 950)
+(eval "(ocaml-run \"String.length \\\"hello\\\"\")")
+(epoch 951)
+(eval "(ocaml-run \"String.uppercase_ascii \\\"hi\\\"\")")
+(epoch 952)
+(eval "(ocaml-run \"String.lowercase_ascii \\\"HI\\\"\")")
+(epoch 953)
+(eval "(ocaml-run \"String.sub \\\"hello\\\" 1 3\")")
+(epoch 954)
+(eval "(ocaml-run \"String.starts_with \\\"he\\\" \\\"hello\\\"\")")
+(epoch 955)
+(eval "(ocaml-run \"String.concat \\\",\\\" [\\\"a\\\"; \\\"b\\\"; \\\"c\\\"]\")")
+
+(epoch 960)
+(eval "(ocaml-run \"Char.code \\\"A\\\"\")")
+(epoch 961)
+(eval "(ocaml-run \"Char.chr 65\")")
+
+(epoch 970)
+(eval "(ocaml-run \"Int.to_string 42\")")
+(epoch 971)
+(eval "(ocaml-run \"Int.of_string \\\"123\\\"\")")
+(epoch 972)
+(eval "(ocaml-run \"Int.abs (-5)\")")
+(epoch 973)
+(eval "(ocaml-run \"Int.max 7 3\")")
+(epoch 974)
+(eval "(ocaml-run \"Int.min 7 3\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1065,6 +1095,23 @@ check 911 "type twice"                   ' -> '
 check 912 "type bool branch"             '"Bool -> Int"'
 check 913 "type not true"                '"Bool"'
 
+# ── Phase 6 String / Char / Int ─────────────────────────────────
+check 950 "String.length"                '5'
+check 951 "String.uppercase_ascii"       '"HI"'
+check 952 "String.lowercase_ascii"       '"hi"'
+check 953 "String.sub"                   '"ell"'
+check 954 "String.starts_with"           'true'
+check 955 "String.concat"                '"a,b,c"'
+
+check 960 "Char.code A"                  '65'
+check 961 "Char.chr 65"                  '"A"'
+
+check 970 "Int.to_string"                '"42"'
+check 971 "Int.of_string"                '123'
+check 972 "Int.abs -5"                   '5'
+check 973 "Int.max"                      '7'
+check 974 "Int.min"                      '3'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"