ocaml: phase 5.1 bf_full.ml baseline (full Brainfuck with [] loops, +++[.-] = 6)

Extends the iter-92 brainfuck.ml subset interpreter with bracket
matching:

  '['  if mem[ptr] = 0, jump past matching ']'
       (forward depth-counting scan: '[' increments depth, ']' decrements)
  ']'  if mem[ptr] <> 0, jump back to matching '['
       (backward depth-counting scan)

Test program '+++[.-]':
  +++   set cell 0 = 3
  [     enter loop (cell != 0)
    .   acc += cell
    -   cell -= 1
  ]     loop while cell != 0
  result: acc = 3 + 2 + 1 = 6

Tests deeply nested while loops, mutable pc / ptr / acc, multi-arm
if/else if dispatch on chars + nested begin/end blocks for loop
body conditionals.

58 baseline programs total.

plans/ocaml-on-sx.md

@@ -407,6 +407,13 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-09 Phase 5.1 — bf_full.ml baseline (Brainfuck interpreter
+  with `[`/`]` loops, `+++[.-]` → 3+2+1 = 6). Extends the iter-92
+  brainfuck.ml subset with bracket matching: `[` jumps past matching
+  `]` if cell is zero (forward depth-counting scan); `]` jumps back
+  to matching `[` if cell is non-zero (backward depth-counting scan).
+  Tests deeply nested while loops, mutable pc + ptr + acc, multi-arm
+  if-else if dispatch on chars. 58 baseline programs total.
 - 2026-05-09 Phase 5.1 — anagram_check.ml baseline (char-frequency
   array, 2/4 pairs are anagrams). to_counts builds a 256-slot int
   array of character frequencies. same_counts compares two arrays