fix(csv-stringify): preserve caller cast configuration

packages/csv-stringify/lib/api/normalize_options.js

@@ -199,8 +199,21 @@ const normalize_options = function (opts) {
   // Normalize option `cast`
   if (options.cast === undefined || options.cast === null) {
     options.cast = {};
-  } else {
-    // todo
+  } else if (
+    typeof options.cast === "object" ||
+    typeof options.cast === "function"
+  ) {
+    options.cast = {
+      ...options.cast,
+      bigint: options.cast.bigint,
+      boolean: options.cast.boolean,
+      date: options.cast.date,
+      number: options.cast.number,
+      object: options.cast.object,
+      string: options.cast.string,
+      null: options.cast.null,
+      undefined: options.cast.undefined,
+    };
   }
   // Normalize option cast.bigint
   if (options.cast.bigint === undefined || options.cast.bigint === null) {

packages/csv-stringify/test/option.cast.js

@@ -1,8 +1,52 @@
 import "should";
+import assert from "node:assert/strict";
 import { stringify } from "../lib/index.js";
 import { stringify as stringifySync } from "../lib/sync.js";
 
 describe("Option `cast`", function () {
+  describe("configuration", function () {
+    for (const frozen of [false, true]) {
+      it(`preserves ${frozen ? "frozen" : "mutable"} options in the sync API`, function () {
+        const string = (value) => value.toUpperCase();
+        const cast = { string, number: null };
+        if (frozen) Object.freeze(cast);
+        for (let i = 0; i < 2; i++) {
+          assert.equal(stringifySync([["value", 42]], { cast }), "VALUE,42\n");
+        }
+        assert.deepEqual(cast, { string, number: null });
+      });
+
+      it(`preserves ${frozen ? "frozen" : "mutable"} options in the callback API`, function (next) {
+        const string = (value) => value.toUpperCase();
+        const cast = { string };
+        if (frozen) Object.freeze(cast);
+        stringify([["value", 42]], { cast }, (err, output) => {
+          if (err) return next(err);
+          assert.equal(output, "VALUE,42\n");
+          assert.deepEqual(cast, { string });
+          next();
+        });
+      });
+    }
+
+    it("preserves inherited and non-enumerable custom casters", function () {
+      const cast = Object.create({ string: (value) => value.toUpperCase() });
+      Object.defineProperty(cast, "number", { value: () => "number" });
+      assert.equal(stringifySync([["value", 42]], { cast }), "VALUE,number\n");
+    });
+
+    it("preserves custom null and undefined casters", function () {
+      const cast = {
+        null: () => "null",
+        undefined: () => "missing",
+      };
+      assert.equal(
+        stringifySync([[null, undefined]], { cast }),
+        "null,missing\n",
+      );
+    });
+  });
+
   describe("udf", function () {
     it("boolean must return a string", function (next) {
       stringify(