ocaml: phase 6 expanded stdlib (+15 tests, 319 total)

List: concat/flatten, init, find/find_opt, partition, mapi/iteri,
assoc/assoc_opt. Option: iter/fold/to_list. Result: get_ok/get_error/
map_error/to_option.

Fixed skip-to-boundary! in parser to track let..in / begin..end /
struct..end / for/while..done nesting via a depth counter — without
this, nested-let inside a top-level decl body trips over the
decl-boundary detector. Stdlib functions like List.init / mapi / iteri
use begin..end to make their nested-let intent explicit.

lib/ocaml/test.sh

@@ -764,6 +764,40 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1323)
 (eval "(ocaml-run-program \"exception E of string ;; try raise (E \\\"oops\\\") with | E s -> s\")")
 
+;; ── Phase 6 expanded stdlib (List/Option/Result extensions) ───
+(epoch 1400)
+(eval "(ocaml-run \"List.concat [[1;2];[3];[4;5]]\")")
+(epoch 1401)
+(eval "(ocaml-run \"List.init 5 (fun i -> i * 10)\")")
+(epoch 1402)
+(eval "(ocaml-run \"List.find_opt (fun x -> x > 2) [1;2;3;4]\")")
+(epoch 1403)
+(eval "(ocaml-run \"List.find_opt (fun x -> x > 99) [1;2;3]\")")
+(epoch 1404)
+(eval "(ocaml-run \"List.mapi (fun i x -> i + x) [10;20;30]\")")
+(epoch 1405)
+(eval "(ocaml-run \"List.partition (fun x -> x > 2) [1;2;3;4]\")")
+(epoch 1406)
+(eval "(ocaml-run \"List.assoc 2 [(1, \\\"a\\\"); (2, \\\"b\\\"); (3, \\\"c\\\")]\")")
+(epoch 1407)
+(eval "(ocaml-run \"List.assoc_opt 99 [(1, \\\"a\\\")]\")")
+
+(epoch 1410)
+(eval "(ocaml-run \"Option.fold 0 (fun x -> x * 10) (Some 7)\")")
+(epoch 1411)
+(eval "(ocaml-run \"Option.fold 0 (fun x -> x * 10) None\")")
+(epoch 1412)
+(eval "(ocaml-run \"Option.to_list (Some 7)\")")
+(epoch 1413)
+(eval "(ocaml-run \"Option.to_list None\")")
+
+(epoch 1420)
+(eval "(ocaml-run \"Result.get_ok (Ok 42)\")")
+(epoch 1421)
+(eval "(ocaml-run \"Result.to_option (Ok 1)\")")
+(epoch 1422)
+(eval "(ocaml-run \"Result.map_error (fun e -> e + 1) (Error 5)\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1210,6 +1244,25 @@ check 1321 "exception arg"                '("exception-def" "MyExn"'
 check 1322 "raise+catch with arg"         '5'
 check 1323 "raise+catch string arg"       '"oops"'
 
+# ── Phase 6 expanded stdlib ─────────────────────────────────────
+check 1400 "List.concat"                  '(1 2 3 4 5)'
+check 1401 "List.init"                    '(0 10 20 30 40)'
+check 1402 "List.find_opt found"          '("Some" 3)'
+check 1403 "List.find_opt missing"        '("None")'
+check 1404 "List.mapi"                    '(10 21 32)'
+check 1405 "List.partition"               '("tuple" (3 4) (1 2))'
+check 1406 "List.assoc"                   '"b"'
+check 1407 "List.assoc_opt missing"       '("None")'
+
+check 1410 "Option.fold Some"             '70'
+check 1411 "Option.fold None"             '0'
+check 1412 "Option.to_list Some"          '(7)'
+check 1413 "Option.to_list None"          '()'
+
+check 1420 "Result.get_ok"                '42'
+check 1421 "Result.to_option Ok"          '("Some" 1)'
+check 1422 "Result.map_error"             '("Error" 6)'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"