Step 12: Parser combinator library — pure SX, 68 tests

lib/parser-combinators.sx — 46 definitions in 8 layers:
  0. Result constructors (make-ok, make-fail, ok?, result-value, etc.)
  1. Primitives (satisfy, parse-char, any-char, parse-string, eof)
  2. Core combinators (fmap, parse-bind, seq, alt, label, lazy-parser)
  3. Repetition (many, many1, optional, skip-many)
  4. Structural (between, sep-by, sep-by1, skip-left, skip-right,
     not-followed-by, look-ahead)
  5. Character classes (digit, letter, alpha-num, whitespace, skip-spaces)
  6. Literal parsers (number-literal, string-literal, identifier)
  7. Run function (run-parser)
  8. SX tokenizer (sx-comment, sx-keyword, sx-symbol, sx-number,
     sx-string, sx-token, sx-tokenize)

Self-tests by tokenizing SX: (define x 42), {:ok true}, (+ 1 (* 2 3)),
comments, negative numbers, nested parens, recursive grammars.

No evaluator changes. Pure HO functions + thunks for lazy recursion.
2868/2868 tests, zero failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/run_tests.ml

@@ -1352,6 +1352,7 @@ let run_spec_tests env test_files =
   load_module "signals.sx" web_dir;   (* web extensions *)
   load_module "freeze.sx" lib_dir;
   load_module "content.sx" lib_dir;
+  load_module "parser-combinators.sx" lib_dir;
   load_module "types.sx" lib_dir;
   load_module "sx-swap.sx" lib_dir;
   (* Shared templates: TW styling engine *)