ocaml: phase 5.1 pretty_table.ml baseline (Buffer + Printf widths, len = 64)

Builds a 4-row scoreboard via Buffer + Printf.sprintf:

  Buffer.add_string buf (Printf.sprintf '%-10s %4d\n' name score)

Each row is exactly 16 chars regardless of actual name/score length:
  10 name padding + 1 space + 4 score padding + 1 newline.
4 rows -> 64 chars total.

Combines:
  - Buffer.add_string + Printf.sprintf
  - %-Ns left-justified string and %Nd right-justified int width
  - List.iter on tuple-pattern args (iter 101 fun (a, b))

42 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -29,6 +29,7 @@
   "mutable_record.ml": 10,
   "option_match.ml": 5,
   "pi_leibniz.ml": 314,
+  "pretty_table.ml": 64,
   "poly_stack.ml": 5,
   "queens.ml": 2,
   "quicksort.ml": 44,

lib/ocaml/baseline/pretty_table.ml

@@ -0,0 +1,10 @@
+let table rows =
+  let buf = Buffer.create 64 in
+  List.iter (fun (name, score) ->
+    Buffer.add_string buf (Printf.sprintf "%-10s %4d\n" name score)
+  ) rows;
+  Buffer.contents buf
+
+;;
+
+String.length (table [("alice", 95); ("bob", 67); ("carol", 100); ("dave", 8)])

plans/ocaml-on-sx.md

@@ -407,6 +407,14 @@ _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 — pretty_table.ml baseline (Buffer + Printf
+  width specifiers, total length 64). Builds a 4-row scoreboard via
+  Buffer + `Printf.sprintf "%-10s %4d\n"`. Each row is exactly 16
+  chars (10 name + 1 space + 4 score + 1 newline) regardless of
+  actual content length thanks to width padding. 4 rows = 64 chars.
+  Combines Buffer.add_string + Printf.sprintf with `%-Ns` /
+  `%Nd` width specifiers + List.iter on tuple-pattern args. 42
+  baseline programs total.
 - 2026-05-09 Phase 4 — bitwise ops `land`/`lor`/`lxor`/`lsl`/`lsr`/
   `asr` + bits.ml baseline (popcount-sum = 21) (+5 tests, 607 total).
   The binop precedence table already had these but eval-op fell