fix: normalise the closed flag and keep return rows closable

Two issues from review.

The endpoint stored whatever integer the caller passed, so `closed=2` was
treated as closed by every truthy check while `validate_closed_source_items`
looks for exactly 1. A submit-authorized caller could suppress a row from
mapping and still submit an invoice against it. Verified: the value persisted
as 2, truthy checks saw it as closed, the guard query did not find it.

`is_item_closable` compared signed amounts, so an unbilled return row with a
negative amount looked already completed and could not be closed. Verified on a
real return Delivery Note: amount -500, billed_amt 0, predicate false.
Magnitudes are compared instead, matching how the percentage funnel already
treats these fields.

erpnext/controllers/accounts_controller.py

@@ -215,9 +215,10 @@ class AccountsController(TransactionBase):
 		"""A row can be closed while anything is still pending on it.
 
 		Billing is the axis every closable document shares; the order doctypes
-		extend this with their own fulfilment axis.
+		extend this with their own fulfilment axis. Amounts are compared as
+		magnitudes so return rows, which carry negative amounts, stay closable.
 		"""
-		return flt(item.billed_amt) < flt(item.amount)
+		return abs(flt(item.billed_amt)) < abs(flt(item.amount))
 
 	def validate(self):
 		clear_closed_rows_on_amend(self)

erpnext/controllers/item_close.py

@@ -47,7 +47,7 @@ def update_closed_status(doctype: str, name: str, item_names: str | list[str], c
 	if not has_closable_items(doctype):
 		frappe.throw(_("Rows of {0} cannot be closed individually").format(_(doctype)))
 
-	closed = cint(closed)
+	closed = 1 if cint(closed) else 0
 	item_names = set(frappe.parse_json(item_names) or [])
 	if not item_names:
 		frappe.throw(_("Select at least one row"))

erpnext/controllers/tests/test_item_close_billing.py

@@ -4,6 +4,7 @@
 import frappe
 
 from erpnext.controllers.item_close import update_closed_status
+from erpnext.controllers.sales_and_purchase_return import make_return_doc
 from erpnext.stock.doctype.delivery_note.mapper import make_sales_invoice
 from erpnext.stock.doctype.delivery_note.test_delivery_note import create_delivery_note
 from erpnext.stock.doctype.item.test_item import make_item
@@ -177,3 +178,26 @@ class TestDeliveryNoteItemClose(ERPNextTestSuite):
 		amended.insert()
 
 		self.assertFalse(any(row.closed for row in amended.items))
+
+	def test_noncanonical_closed_value_is_normalised(self):
+		"""A truthy non-1 value must not slip past the exact-match submission guard."""
+		note = self.make_delivery_note()
+
+		update_closed_status("Delivery Note", note.name, [note.items[1].name], 2)
+
+		note.reload()
+		self.assertEqual(note.items[1].closed, 1)
+
+	def test_unbilled_return_row_can_be_closed(self):
+		"""Return rows carry negative amounts and must still be closable."""
+		note = self.make_delivery_note()
+		return_note = make_return_doc("Delivery Note", note.name)
+		return_note.insert()
+		return_note.submit()
+
+		row = return_note.items[0]
+		self.assertLess(row.amount, 0)
+		self.assertTrue(return_note.is_item_closable(row))
+
+		self.close_items(return_note, [row])
+		self.assertTrue(return_note.items[0].closed)