Recover agent-loop progress: lua/prolog/forth/erlang/haskell phases 1-2

Salvaged from worktree-agent-* branches killed during sx-tree MCP outage:
- lua: tokenizer + parser + phase-2 transpile (~157 tests)
- prolog: tokenizer + parser + unification (72 tests, plan update lost to WIP)
- forth: phase-1 reader/interpreter + phase-2 colon/VARIABLE (134 tests)
- erlang: tokenizer + parser (114 tests)
- haskell: tokenizer + parse tests (43 tests)

Cherry-picked file contents only, not branch history, to avoid pulling in
unrelated ocaml-vm merge commits that were in those branches' bases.

lib/erlang/parser-core.sx

@@ -0,0 +1,49 @@
+;; Core parser helpers — shared by er-parse-expr and er-parse-module.
+;; Everything reads/mutates a parser state dict:
+;;   {:toks TOKS :idx INDEX}
+
+(define er-state-make (fn (toks) {:idx 0 :toks toks}))
+
+(define
+  er-peek
+  (fn
+    (st offset)
+    (let
+      ((toks (get st :toks)) (idx (+ (get st :idx) offset)))
+      (if (< idx (len toks)) (nth toks idx) (nth toks (- (len toks) 1))))))
+
+(define er-cur (fn (st) (er-peek st 0)))
+
+(define er-cur-type (fn (st) (get (er-cur st) :type)))
+(define er-cur-value (fn (st) (get (er-cur st) :value)))
+
+(define er-advance! (fn (st) (dict-set! st :idx (+ (get st :idx) 1))))
+
+(define er-at-eof? (fn (st) (= (er-cur-type st) "eof")))
+
+(define
+  er-is?
+  (fn
+    (st type value)
+    (and
+      (= (er-cur-type st) type)
+      (or (= value nil) (= (er-cur-value st) value)))))
+
+(define
+  er-expect!
+  (fn
+    (st type value)
+    (if
+      (er-is? st type value)
+      (let ((t (er-cur st))) (er-advance! st) t)
+      (error
+        (str
+          "Erlang parse: expected "
+          type
+          (if value (str " '" value "'") "")
+          " but got "
+          (er-cur-type st)
+          " '"
+          (er-cur-value st)
+          "' at pos "
+          (get (er-cur st) :pos))))))