fix: enforce date validation for custom sections in edit mode (#1260)

Remove isEditMode bypass for start and end date validation. This ensures
  scheduled or live sections always have dates on or after today, even when
  editing existing sections, and validates manually typed dates that bypass
  the date picker's minDate constraint.

Author: jwalterss

src/curated-corpus/components/CustomSectionForm/CustomSectionForm.validation.ts

@@ -45,10 +45,9 @@ export const getValidationSchema = (isEditMode: boolean = false) => {
         'not-in-past',
         'Start date cannot be in the past',
         function (value) {
-          // TODO(HNT-1125): Remove the edit-mode bypass and enforce start-date validation
-          // for manually typed values once editorial confirms we should always require
-          // startDate >= today for new and existing sections.
-          if (!value || isEditMode) {
+          // Always enforce start date validation, even in edit mode
+          // This ensures scheduled or live sections always start on or after today
+          if (!value) {
             return true;
           }
           const startDate = DateTime.fromJSDate(value).startOf('day');
@@ -60,7 +59,8 @@ export const getValidationSchema = (isEditMode: boolean = false) => {
       .date()
       .nullable()
       .test('not-in-past', 'End date cannot be in the past', function (value) {
-        if (!value || isEditMode) {
+        // Always enforce end date validation, even in edit mode
+        if (!value) {
           return true;
         }
         const endDate = DateTime.fromJSDate(value).startOf('day');