feat(19.3-04): purge the host site's page cache after FAQ saves and deletes

- FormAfterCreate/FormAfterUpdate run the locale check, then register a
  purge of kind faq through cooler.PurgeSiteCacheAfterCommit
- new FormAfterDelete purges after the delete commits
- purgeSiteCache helper takes the save transaction from cabana.TxFromContext
  and the purger from cooler.SiteCacheFromApp (site_cache.* keys)
- TestFaqAdminPurgesSiteCache on Postgres

controllers/faqs.go

@@ -49,16 +49,39 @@ func (faqsAdminController) AdminFieldRelations() []cabana.FieldRelationContract
 // errLocaleRequired is the field message of a FAQ saved without a locale.
 const errLocaleRequired = "golem15.faq::lang.errors.locale_required"
 
+// siteCacheKind is the kind a FAQ save's site-cache purge carries.
+const siteCacheKind = "faq"
+
 // FormAfterCreate refuses a FAQ without a locale. cabana writes locale_id
 // from the relation field after the model rules ran, so the check runs here,
-// inside the save's transaction: the refusal rolls the row back.
-func (faqsAdminController) FormAfterCreate(_ context.Context, model any) error {
-	return requireLocale(model)
+// inside the save's transaction: the refusal rolls the row back. A FAQ that
+// passes purges the host site's page caches once the save commits.
+func (c faqsAdminController) FormAfterCreate(ctx context.Context, model any) error {
+	return c.afterSave(ctx, model)
 }
 
-// FormAfterUpdate applies the same check to an update.
-func (faqsAdminController) FormAfterUpdate(_ context.Context, model any) error {
-	return requireLocale(model)
+// FormAfterUpdate applies the same check and purge to an update.
+func (c faqsAdminController) FormAfterUpdate(ctx context.Context, model any) error {
+	return c.afterSave(ctx, model)
+}
+
+// FormAfterDelete purges the host site's page caches once the delete
+// commits.
+func (c faqsAdminController) FormAfterDelete(ctx context.Context, model any) error {
+	if faq, ok := model.(*models.FAQ); ok && faq != nil {
+		purgeSiteCache(ctx, c.app, siteCacheKind, faq.Slug)
+	}
+	return nil
+}
+
+func (c faqsAdminController) afterSave(ctx context.Context, model any) error {
+	if err := requireLocale(model); err != nil {
+		return err
+	}
+	if faq, ok := model.(*models.FAQ); ok && faq != nil {
+		purgeSiteCache(ctx, c.app, siteCacheKind, faq.Slug)
+	}
+	return nil
 }
 
 func requireLocale(model any) error {
@@ -72,6 +95,7 @@ func requireLocale(model any) error {
 var (
 	_ pact.FormAfterCreate         = faqsAdminController{}
 	_ pact.FormAfterUpdate         = faqsAdminController{}
+	_ pact.FormAfterDelete         = faqsAdminController{}
 	_ pact.AdminController         = faqsAdminController{}
 	_ pact.AdminPermissioned       = faqsAdminController{}
 	_ pact.AdminRecordSource       = faqsAdminController{}