fix(core-shared): narrow Payload Field union before accessing name in tests

Payload's Field type is a discriminated union; field.name only exists on
named variants. Tests now narrow on type (and 'name' in field for groups)
before reading variant-specific properties.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core-shared/src/payload/fields/seo-fields.test.ts

@@ -3,6 +3,9 @@ import { seoFields } from "./seo-fields";
 
 describe("seoFields", () => {
   it("is a group field named 'seo'", () => {
+    if (seoFields.type !== "group" || !("name" in seoFields)) {
+      throw new Error("seoFields must be a named group");
+    }
     expect(seoFields.name).toBe("seo");
     expect(seoFields.type).toBe("group");
   });

packages/core-shared/src/payload/fields/slug-field.test.ts

@@ -4,8 +4,8 @@ import { slugField } from "./slug-field";
 describe("slugField", () => {
   it("returns a Payload Field with default name 'slug'", () => {
     const field = slugField();
+    if (field.type !== "text") throw new Error("expected text field");
     expect(field.name).toBe("slug");
-    expect(field.type).toBe("text");
     expect(field.required).toBe(true);
     expect(field.unique).toBe(true);
     expect(field.index).toBe(true);
@@ -13,6 +13,7 @@ describe("slugField", () => {
 
   it("accepts a custom field name", () => {
     const field = slugField("permalink");
+    if (field.type !== "text") throw new Error("expected text field");
     expect(field.name).toBe("permalink");
   });
 });