fix: keep source rate on bulk apply_price_list when maintain same rate is on

The single-row re-fetch guard skipped the bulk apply_price_list path, so
changing the price list, party, or conversion rate on a mapped transaction
re-fetched current Item Prices and overwrote the mapped rates, breaking the
maintain-same-rate check on save.

Guard apply_price_list_on_item with the same source-row lookup, and resolve the
parent doctype via ctx.parenttype since the bulk path carries the child doctype
in ctx.doctype.

erpnext/stock/get_item_details.py

@@ -210,7 +210,10 @@ def get_rate_locked_source_row(ctx: ItemDetailsCtx, doc) -> frappe._dict | None:
 	Order) can only be saved at the source rate. Fetching a newer Item Price here
 	would set a rate the document can never be saved with, so keep the source rate.
 	"""
-	source_fields = maintain_same_rate_source_fields.get(ctx.doctype)
+	if isinstance(doc, str):
+		doc = json.loads(doc)
+
+	source_fields = maintain_same_rate_source_fields.get(ctx.parenttype or ctx.doctype)
 	if not source_fields or not doc or ctx.get("is_return") or not maintain_same_rate_enabled(ctx):
 		return None
 
@@ -221,7 +224,7 @@ def get_rate_locked_source_row(ctx: ItemDetailsCtx, doc) -> frappe._dict | None:
 
 
 def maintain_same_rate_enabled(ctx: ItemDetailsCtx) -> bool:
-	if ctx.doctype in purchase_doctypes:
+	if (ctx.parenttype or ctx.doctype) in purchase_doctypes:
 		if ctx.get("is_internal_supplier"):
 			return False
 		return bool(cint(frappe.get_cached_value("Buying Settings", "None", "maintain_same_rate")))
@@ -1694,7 +1697,14 @@ def apply_price_list(ctx: ItemDetailsCtx, as_doc: bool = False, doc: Document |
 
 def apply_price_list_on_item(ctx, doc=None):
 	item_doc = frappe.get_cached_doc("Item", ctx.item_code)
-	item_details = get_price_list_rate(ctx, item_doc)
+
+	source_row = get_rate_locked_source_row(ctx, doc)
+	if source_row:
+		item_details = frappe._dict(
+			price_list_rate=flt(source_row.get("price_list_rate")) or flt(source_row.get("rate"))
+		)
+	else:
+		item_details = get_price_list_rate(ctx, item_doc)
 
 	ctx.conversion_factor = flt(ctx.conversion_factor) or get_conversion_factor(ctx.item_code, ctx.uom).get(
 		"conversion_factor", 1

erpnext/stock/tests/test_get_item_details.py

@@ -196,3 +196,66 @@ class TestGetItemDetail(ERPNextTestSuite):
 		# Control: without the setting the newer Item Price would be fetched.
 		set_maintain_same_rate(0)
 		self.assertEqual(fetch_price_list_rate(), 120)
+
+	def test_apply_price_list_keeps_source_rate_when_maintain_same_rate(self):
+		"""#57436: the bulk apply_price_list path (price list / party / conversion rate
+		change) must also keep the source rate on mapped rows, not just re-fetch of a
+		single row. Here a PR row carries its PO rate (175) while the current price list
+		rate is 100; the bulk apply must keep 175.
+		"""
+		from frappe.utils import flt, nowdate
+
+		from erpnext.buying.doctype.purchase_order.test_purchase_order import create_purchase_order
+		from erpnext.stock.get_item_details import apply_price_list
+
+		item_code = "_Test Item"
+		price_list = "_Test Buying Price List"
+
+		original = frappe.db.get_single_value("Buying Settings", "maintain_same_rate")
+		frappe.db.set_single_value("Buying Settings", "maintain_same_rate", 1)
+		frappe.clear_cache(doctype="Buying Settings")
+
+		try:
+			po = create_purchase_order(item_code=item_code, rate=175, qty=1)
+
+			row_name = "pr-row-1"
+			pr_doc = {
+				"doctype": "Purchase Receipt",
+				"items": [
+					{
+						"name": row_name,
+						"item_code": item_code,
+						"purchase_order_item": po.items[0].name,
+						"price_list_rate": 175,
+						"rate": 175,
+					}
+				],
+			}
+			ctx = frappe._dict(
+				doctype="Purchase Receipt",
+				supplier=po.supplier,
+				company=po.company,
+				currency=po.currency,
+				conversion_rate=1.0,
+				price_list=price_list,
+				plc_conversion_rate=1.0,
+				transaction_date=nowdate(),
+				items=[
+					frappe._dict(
+						doctype="Purchase Receipt Item",
+						parenttype="Purchase Receipt",
+						item_code=item_code,
+						child_docname=row_name,
+						qty=1,
+						uom=po.items[0].uom,
+						stock_uom=po.items[0].stock_uom,
+						conversion_factor=1.0,
+					)
+				],
+			)
+
+			result = apply_price_list(ctx, doc=pr_doc)
+			self.assertEqual(flt(result["children"][0].get("price_list_rate")), 175)
+		finally:
+			frappe.db.set_single_value("Buying Settings", "maintain_same_rate", original)
+			frappe.clear_cache(doctype="Buying Settings")