[GraphQl 2.4.2] subtotal_with_discount_excluding_tax is calculated using discount including tax

[Hexmage]

Preconditions (*)

1. Magento 2.4.2
2. tax/calculation/price_includes_tax = including tax
3. tax/calculation/apply_after_discount = after discount
4. tax/calculation/discount_tax = including tax

Steps to reproduce (*)

1. Create a cart and add a product that's worth 1000 (incl tax) with a tax% of 25%.
2. Set a discount on the cart for 10.
3. Do the following graphql request

query getCartDetails($cartId: String!) {
	cart(cart_id: $cartId) {
                 prices {
			applied_taxes {
				amount {
					value
				}
			}
			discount {
				amount {
					value
				}
			}
			subtotal_including_tax {
				value
			}
			subtotal_excluding_tax {
				value
			}
                        subtotal_with_discount_excluding_tax {
				value
			}
			grand_total {
				value			
                        }
		}
	}
}

Expected result (*)

{
    "data": {
        "cart": {
            "prices": {
                "applied_taxes": [
                    {
                        "amount": {
                            "value": 198
                        }
                    }
                ],
                "discount": {
                    "amount": {
                        "value": -10
                    }
                },
                "subtotal_including_tax": {
                    "value": 1000
                },
                "subtotal_excluding_tax": {
                    "value": 800
                },
                "subtotal_with_discount_excluding_tax": {
                    "value": 792
                },
                "grand_total": {
                    "value": 990
                }
            }
        }
    }
}

"subtotal_with_discount_excluding_tax" should be 1000 - 10 - 198 = 792
Which is same as 800 (Sub total) - 8 (Sub total discount) = 792

Actual result (*)

{
    "data": {
        "cart": {
            "prices": {
                "applied_taxes": [
                    {
                        "amount": {
                            "value": 198
                        }
                    }
                ],
                "discount": {
                    "amount": {
                        "value": -10
                    }
                },
                "subtotal_including_tax": {
                    "value": 1000
                },
                "subtotal_excluding_tax": {
                    "value": 800
                },
                "subtotal_with_discount_excluding_tax": {
                    "value": 790
                },
                "grand_total": {
                    "value": 990
                }
            }
        }
    }
}

UI Issue: Payment Breakup details sum is not matching with Grand Total.
800 - 10 + 198 = 988 but not 990

---

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[m2-assistant]

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[m2-assistant]

Hi @engcom-November. Thank you for working on this issue.
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  Details

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  Details

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[engcom-November]

Verified the issue on Magento2.4-develop branch and the issue is reproducible on both Frontend and GraphQl response as well:
Steps performed:
Stores - Settings - Configuration - Sales - Tax - Set Catalog Prices - Including Tax
Apply Discount On Prices - Including Tax
Apply Customer Tax - After Discount and Save
Create a cart and add a product that's worth 1000 (incl tax) with a tax% of 25%.
Set a discount on the cart for $10 fixed amount for whole Cart.
Run "GetCartDetails" GraphQL request:
Issue: Response: "subtotal_with_discount_excluding_tax" is updated as subtotal - discount - total tax without discount
UI Issue: Payment Breakup details sum is not matching with Grand Total.
800 - 10 + 198 = 988 but not 990
Expected behavior:
"subtotal_with_discount_excluding_tax" should be updated as subtotal - discount - total tax with discount