fix: rebalance batch slot values at the pooled rate when driven negative

A batch is one valuation pool, so consumption is valued at the pooled
rate while slots may carry stale intra-batch detail (e.g. units
reconciled at zero and later merged). Consuming such a slot leaves a
negative value on positive qty. Spread the pool value across the
batch's slots when that happens; non-batchwise slots pool per
warehouse.

erpnext/stock/report/stock_ageing/stock_ageing.py

@@ -325,6 +325,7 @@ class FIFOSlots:
 			del stock_ledger_entries
 
 		self._recompute_moving_average_slots()
+		self._rebalance_negative_batch_slots()
 
 		if not self.filters.get("show_warehouse_wise_stock"):
 			# (Item 1, WH 1), (Item 1, WH 2) => (Item 1)
@@ -346,6 +347,33 @@ class FIFOSlots:
 				if is_qty_slot(slot):
 					slot[FIFO_VALUE_INDEX] = flt(slot[FIFO_QTY_INDEX] * rate)
 
+	def _rebalance_negative_batch_slots(self) -> None:
+		for item_dict in self.item_details.values():
+			if item_dict.get("has_batch_no"):
+				self._rebalance_negative_batch_slot_values(item_dict["fifo_queue"])
+
+	def _rebalance_negative_batch_slot_values(self, fifo_queue: list) -> None:
+		"""A batch is one valuation pool, so a slot driven negative by consumption
+		at the pooled rate is stale detail: spread the pool value over its slots."""
+		groups = {}
+		for slot in fifo_queue:
+			if is_batch_slot(slot):
+				key = slot[BATCH_SLOT_BATCH_INDEX] if slot[BATCH_SLOT_VALUATION_INDEX] else None
+				groups.setdefault(key, []).append(slot)
+
+		for slots in groups.values():
+			has_negative_slot = any(
+				flt(slot[BATCH_SLOT_VALUE_INDEX]) < 0 and flt(slot[BATCH_SLOT_QTY_INDEX]) > 0
+				for slot in slots
+			)
+			total_qty = sum(flt(slot[BATCH_SLOT_QTY_INDEX]) for slot in slots)
+			if not has_negative_slot or total_qty <= 0:
+				continue
+
+			rate = sum(flt(slot[BATCH_SLOT_VALUE_INDEX]) for slot in slots) / total_qty
+			for slot in slots:
+				slot[BATCH_SLOT_VALUE_INDEX] = flt(slot[BATCH_SLOT_QTY_INDEX] * rate)
+
 	def _get_bundle_wise_details(self, stock_ledger_entries: list | None) -> tuple[dict, dict]:
 		if stock_ledger_entries is not None:
 			return frappe._dict({}), frappe._dict({})

erpnext/stock/report/stock_ageing/test_stock_ageing.py

@@ -616,6 +616,58 @@ class TestStockAgeing(ERPNextTestSuite):
 			],
 		)
 
+	def test_batch_issue_at_pooled_rate_keeps_slot_values_positive(self):
+		"""Ledger (same wh, batch B): [+10 @ 0, +10 @ 10, -4 @ pooled 5]
+		Consuming the zero-valued head slot at the pooled rate drives it
+		negative; slot values are then rebalanced to the batch pool rate."""
+		from erpnext.stock.doctype.item.test_item import make_item
+
+		item_code = make_item(
+			"Test Stock Ageing Batch Pool Rebalance",
+			{"is_stock_item": 1, "has_batch_no": 1, "valuation_method": "FIFO"},
+		).name
+
+		batch_no = "SA-POOL-REBALANCE-BATCH"
+		if not frappe.db.exists("Batch", batch_no):
+			frappe.get_doc({"doctype": "Batch", "batch_id": batch_no, "item": item_code}).insert(
+				ignore_permissions=True
+			)
+		frappe.db.set_value("Batch", batch_no, "use_batchwise_valuation", 1)
+
+		def make_sle(posting_date, voucher_no, actual_qty, qty_after, stock_value_difference):
+			return frappe._dict(
+				name=item_code,
+				actual_qty=actual_qty,
+				qty_after_transaction=qty_after,
+				stock_value_difference=stock_value_difference,
+				valuation_rate=abs(stock_value_difference / actual_qty) if actual_qty else 0,
+				warehouse="WH 1",
+				posting_date=posting_date,
+				voucher_type="Stock Entry",
+				voucher_no=voucher_no,
+				has_serial_no=False,
+				has_batch_no=True,
+				serial_no=None,
+				batch_no=batch_no,
+			)
+
+		sle = [
+			make_sle("2021-12-01", "001", 10, 10, 0),
+			make_sle("2021-12-02", "002", 10, 20, 100),
+			make_sle("2021-12-03", "003", -4, 16, -20),
+		]
+
+		slots = FIFOSlots(self.filters, sle).generate()
+		queue = slots[item_code]["fifo_queue"]
+
+		self.assertEqual(
+			queue,
+			[
+				[batch_no, 1, 6.0, "2021-12-01", 30.0],
+				[batch_no, 1, 10.0, "2021-12-01", 50.0],
+			],
+		)
+
 	def test_sequential_stock_reco_same_warehouse(self):
 		"""
 		Test back to back stock recos (same warehouse).