Prevent shifting of non-billable absent baskets

Baskets from the included absences quota (absences_included) are not billable - members aren't charged for these as part of their subscription. Allowing these to be shifted would move the content to a billable target basket, causing members to pay for content that should have been included in their quota.

This change adds a `billable?` check to `can_be_shifted?`, ensuring only billable absent baskets can be shifted. This makes the logic consistent with `can_force?` which handles the case where members want to receive a basket on an included absence date.

Also extracts the line-through styling condition into a `content_forfeited?` predicate method for clarity in the member basket view.

Updated handbook documentation in all languages to clarify that included absences cannot be shifted.

Author: thibaudgg

app/models/basket/shifting.rb

@@ -19,7 +19,15 @@ module Basket::Shifting
   end
 
   def can_be_shifted?
-    absent? && !empty? && !shifted?
+    absent? && !empty? && !shifted? && billable?
+  end
+
+  # Returns true when an absent basket's content is forfeited (won't be received).
+  # This happens when the basket is not billable (from absences_included quota)
+  # or empty. Shifted baskets are also forfeited on the source date (content
+  # moves to target date, so nothing delivered here).
+  def content_forfeited?
+    absent? && (!billable? || empty?)
   end
 
   def shifted?

app/views/handbook/absences.de.md.erb

@@ -23,7 +23,7 @@ Auf der Mitgliederseite ist die Taschenverschiebung standardmäßig nicht mögli
 
 Wenn die Abwesenheit storniert wird, wird der Tascheninhalt automatisch zu seiner ursprünglichen Lieferung zurückgebracht.
 
-> Taschenverschiebungen sind nur möglich, wenn Abwesenheiten in Rechnung gestellt werden.
+> Taschenverschiebungen sind nur für kostenpflichtige Abwesenheiten möglich. Inbegriffene Abwesenheiten (nicht kostenpflichtig) können nicht verschoben werden.
 
 ### Newsletter-Vorlage
 

app/views/handbook/absences.en.md.erb

@@ -23,7 +23,7 @@ On the member side, basket shifting is not possible by default. To activate this
 
 If the absence is cancelled, the basket content will be automatically restored to its original delivery.
 
-> Basket shifting is only possible if absences are billed.
+> Basket shifting is only possible for billable absences. Included absences (non-billable) cannot be shifted.
 
 ### Newsletter Template
 

app/views/handbook/absences.fr.md.erb

@@ -23,7 +23,7 @@ Côté membre, le déplacement de paniers n'est pas possible par défaut. Pour a
 
 Si l'absence est annulée, le contenu du panier sera automatiquement restitué à sa livraison d'origine.
 
-> Le déplacement de paniers est possible uniquement si les absences sont facturées.
+> Le déplacement de paniers est possible uniquement pour les absences facturées. Les absences incluses (non facturées) ne peuvent pas être déplacées.
 
 ### Template de newsletter
 

app/views/handbook/absences.it.md.erb

@@ -23,7 +23,7 @@ Dal lato del socio, lo spostamento di cestini non è possibile per impostazione
 
 Se l'assenza viene annullata, il contenuto del cestino sarà automaticamente restituito alla sua consegna originale.
 
-> Lo spostamento di cestini è possibile solo se le assenze vengono fatturate.
+> Lo spostamento di cestini è possibile solo per le assenze fatturate. Le assenze incluse (non fatturate) non possono essere spostate.
 
 ### Template di newsletter
 

app/views/handbook/absences.nl.md.erb

@@ -23,7 +23,7 @@ Aan de ledenkant is pakketverschuiving standaard niet mogelijk. Om deze functie
 
 Als de afwezigheid wordt geannuleerd, wordt de pakketinhoud automatisch hersteld naar zijn oorspronkelijke levering.
 
-> Pakketverschuiving is alleen mogelijk als afwezigheid wordt gefactureerd.
+> Pakketverschuiving is alleen mogelijk voor gefactureerde afwezigheid. Inbegrepen afwezigheid (niet gefactureerd) kan niet worden verschoven.
 
 ### Nieuwsbrief Template
 

app/views/members/baskets/_basket.html.erb

@@ -42,7 +42,7 @@
     </div>
   </div>
 
-  <ul class="-ms-0.5 space-y-1.5 <%= "[&_a]:decoration-inherit line-through" if basket.absent? && (!basket.billable? || basket.empty?) %>">
+  <ul class="-ms-0.5 space-y-1.5 <%= "[&_a]:decoration-inherit line-through" if basket.content_forfeited? %>">
     <li class="flex flex-row items-center gap-2">
       <%= icon "shopping-bag", class: "flex-none size-5 text-gray-300 dark:text-gray-700" %>
 

test/models/basket/shifting_test.rb

@@ -3,6 +3,95 @@
 require "test_helper"
 
 class Basket::ShiftingTest < ActiveSupport::TestCase
+  test "can_be_shifted? returns true for absent billable basket" do
+    basket = baskets(:jane_5)
+
+    assert basket.absent?
+    assert basket.billable?
+    assert_not basket.empty?
+    assert_not basket.shifted?
+    assert basket.can_be_shifted?
+  end
+
+  test "can_be_shifted? returns false for absent non-billable basket" do
+    basket = baskets(:jane_5)
+    basket.update_column(:billable, false)
+
+    assert basket.absent?
+    assert_not basket.billable?
+    assert_not basket.can_be_shifted?
+  end
+
+  test "can_be_shifted? returns false for non-absent basket" do
+    basket = baskets(:jane_6)
+
+    assert_not basket.absent?
+    assert basket.billable?
+    assert_not basket.can_be_shifted?
+  end
+
+  test "can_be_shifted? returns false for empty absent basket" do
+    basket = baskets(:jane_5)
+    basket.update_columns(quantity: 0)
+    basket.baskets_basket_complements.delete_all
+
+    assert basket.absent?
+    assert basket.billable?
+    assert_empty basket
+    assert_not basket.can_be_shifted?
+  end
+
+  test "can_be_member_shifted? returns false for non-billable absent basket" do
+    org(basket_shifts_annually: 1)
+    basket = baskets(:jane_5)
+    basket.update_column(:billable, false)
+
+    assert basket.absent?
+    assert_not basket.billable?
+    assert_not basket.can_be_shifted?
+    assert_not basket.can_be_member_shifted?
+  end
+
+  test "content_forfeited? returns true for non-billable absent basket" do
+    basket = baskets(:jane_5)
+    basket.update_column(:billable, false)
+
+    assert basket.absent?
+    assert_not basket.billable?
+    assert basket.content_forfeited?
+  end
+
+  test "content_forfeited? returns true for empty absent basket" do
+    basket = baskets(:jane_5)
+    basket.update_columns(quantity: 0)
+    basket.baskets_basket_complements.delete_all
+
+    assert basket.absent?
+    assert basket.billable?
+    assert_empty basket
+    assert basket.content_forfeited?
+  end
+
+  test "content_forfeited? returns false for billable non-empty absent basket" do
+    basket = baskets(:jane_5)
+
+    assert basket.absent?
+    assert basket.billable?
+    assert_not basket.empty?
+    assert_not basket.content_forfeited?
+  end
+
+  test "content_forfeited? returns true for shifted basket (empty on source date)" do
+    basket = baskets(:jane_5)
+    basket.update!(shift_target_basket_id: baskets(:jane_8).id)
+    basket.reload
+
+    assert basket.absent?
+    assert basket.shifted?
+    assert_empty basket, "shifted basket is empty (quantity decremented)"
+    assert basket.content_forfeited?, "shifted basket is forfeited on source date (nothing delivered here)"
+  end
+
   test "decline shift" do
     basket = baskets(:jane_5)
     assert basket.can_be_shifted?