fix(record): derive headers and to_row from a single columns list

Make alignment impossible: both headers and to_row are derived from a single
list of (name, extractor) pairs, so reordering one without the other is
impossible. CSV schema cannot silently mislabel columns.

Add a meaningful test that pins the header names in order, not just length.
This catches column reordering regressions.

1 files changed, 7 insertions, 1 deletions

diff --git a/test/test_names.ml b/test/test_names.ml
index 3ddf79c..1649f9e 100644
--- a/test/test_names.ml
+++ b/test/test_names.ml
@@ -130,7 +130,13 @@ let test_record () =
   (* A day outside a numbered week renders week as the empty string, not "0". *)
   let r' = Rec.of_temporal ~rite:"ef" demo_vocab date { t with Tmp.week = None } in
   Alcotest.(check string) "no week" "" r'.Rec.week;
-  Alcotest.(check int) "row matches headers" (List.length Rec.headers)
+  (* Schema is pinned: headers and to_row derive from a single columns list,
+     so alignment cannot drift. Assert the column names in order. *)
+  Alcotest.(check (list string)) "headers schema"
+    [ "date"; "rite"; "season"; "week"; "weekday"; "slug"; "rank"; "colour"; "subject" ]
+    Rec.headers;
+  (* Row must be the same length and order as headers. *)
+  Alcotest.(check int) "row matches headers length" (List.length Rec.headers)
     (List.length (Rec.to_row r))
 
 let suite =