ocaml: phase 2 try/with + raise (+6 tests, 204 total)

Parser: try EXPR with | pat -> handler | ... -> (:try EXPR CLAUSES).
Eval delegates to SX guard with else matching the raised value against
clause patterns; re-raises on no-match. raise/failwith/invalid_arg
shipped as builtins. failwith "msg" raises ("Failure" msg) so
| Failure msg -> ... patterns match.

plans/ocaml-on-sx.md

@@ -156,7 +156,8 @@ SX CEK evaluator (both JS and OCaml hosts)
 - [ ] Mutable record fields.
 - [x] `for i = lo to hi do ... done` loop; `while cond do ... done` (incl.
       `downto` direction).
-- [ ] `try`/`with` — maps to SX `guard`; `raise` via perform.
+- [x] `try`/`with` — maps to SX `guard`; `raise` is a builtin that calls
+      host SX `raise`. `failwith` and `invalid_arg` ship as builtins.
 - [ ] Tests in `lib/ocaml/tests/eval.sx` — 50+ tests, pure + imperative.
 
 ### Phase 3 — ADTs + pattern matching
@@ -320,6 +321,12 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 2 — `try`/`with` + `raise` builtin. Parser produces
+  `(:try EXPR CLAUSES)`; eval delegates to SX `guard` with `else`
+  matching the raised value against clause patterns and re-raising on
+  no-match. `raise`/`failwith`/`invalid_arg` exposed as builtins;
+  failwith builds `("Failure" msg)` so `Failure msg -> ...` patterns
+  match. 204/204 (+6).
 - 2026-05-08 Phase 2 — `function | pat -> body | …` parser + eval.
   Sugar for `fun x -> match x with | …`. AST: `(:function CLAUSES)`
   evaluated to a unary closure that runs `ocaml-match-clauses` on the