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, 17 insertions, 4 deletions

diff --git a/lib/kernel/record.ml b/lib/kernel/record.ml
index af55f07..425aad5 100644
--- a/lib/kernel/record.ml
+++ b/lib/kernel/record.ml
@@ -33,8 +33,21 @@ let of_temporal ~rite vocab date (t : ('s, 'r) Temporal.t) =
         cel.Celebration.citations;
   }
 
-let headers =
-  [ "date"; "rite"; "season"; "week"; "weekday"; "slug"; "rank"; "colour"; "subject" ]
+(* Scalar columns, each with a (name, extractor) pair. Derived from this single
+   source ensures headers and to_row cannot drift apart. Names and citations are
+   excluded: they are variable-arity and belong to richer encoders in Plan 5. *)
+let columns =
+  [ ("date",    fun r -> r.date);
+    ("rite",    fun r -> r.rite);
+    ("season",  fun r -> r.season);
+    ("week",    fun r -> r.week);
+    ("weekday", fun r -> r.weekday);
+    ("slug",    fun r -> r.slug);
+    ("rank",    fun r -> r.rank);
+    ("colour",  fun r -> r.colour);
+    ("subject", fun r -> r.subject);
+  ]
 
-let to_row r =
-  [ r.date; r.rite; r.season; r.week; r.weekday; r.slug; r.rank; r.colour; r.subject ]
+let headers = List.map fst columns
+
+let to_row r = List.map (fun (_, get) -> get r) columns