[FIX] purchase_stock_ux: cancel remaining must not leave a pending vendor receipt nor a counter-delivery

[fw-bot-adhoc]

Problem

When cancelling the remaining qty on a purchase order line (button_cancel_remaining), lowering product_qty does not always cancel the pending receipt:

• Refund return (ticket 124773): after receiving and returning to the vendor with to refund, a live pending IN move survives. The forecast keeps showing units "to receive" that will never arrive.
• Negative move that does not net (ticket 124957): when the negative move can't merge against the pending one (different price / final location), a counter-delivery (OUT) to the vendor is generated instead of cancelling the remainder.

Fix

After setting product_qty, explicitly cancel the line's open remaining move, scoped to genuine forward vendor receipts:

rec.move_ids.filtered(
    lambda m: m.state not in ("done", "cancel")
    and not m._is_exchange_move_helper()       # exchange-return replacement: legit expected receipt
    and not m.origin_returned_move_id          # open vendor return: not part of the remainder
).with_context(cancel_from_order=True)._action_cancel()

In 1/2/3-step receptions the pending qty always lives in the first-step move (vendor→input), which hangs off move_ids and has no downstream; core _action_cancel propagates to later moves if needed (and never to done ones), so there's no need to walk the chain. product_qty is not touched, so invoicing (qty_to_invoice) stays intact.

The two exclusions matter because returns and exchange replacements also carry purchase_line_id and thus land in move_ids; without the guards, an open (not-yet-validated) vendor return would be cancelled along with the remainder.

Also replaced the expensive fields_get() probe in _is_exchange_move_helper with a plain 'is_exchange_move' in self._fields check (O(1), no full field-descriptor build).

Tests

test_cancel_remaining.py, parametrized over one/two/three steps:

• partial receipt → cancel remaining closes the line
• refund return then cancel remaining (124773) → no pending/inflated IN
• goods already received in transit are preserved
• open vendor return must survive cancel remaining (RED without the origin_returned_move_id guard; reproduces the over-cancel reported on the client base)

All green on a v18 test DB (0 failed, 0 error of 4 tests).

Forward-Port-Of: #358

[roboadhoc]

[fw-bot-adhoc]

@jcadhoc @les-adhoc cherrypicking of pull request #358 failed.

stdout:

Auto-merging purchase_stock_ux/__manifest__.py
CONFLICT (content): Merge conflict in purchase_stock_ux/__manifest__.py
Auto-merging purchase_stock_ux/models/purchase_order_line.py
Auto-merging purchase_stock_ux/models/stock_move.py
CONFLICT (content): Merge conflict in purchase_stock_ux/models/stock_move.py

Either perform the forward-port manually (and push to this branch, proceeding as usual) or close this PR (maybe?).

you can use git-fw to re-do the forward-port for you locally.

⚠️ after resolving this conflict, you will need to merge it via @roboadhoc.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[fw-bot-adhoc]

@jcadhoc @les-adhoc this forward port of #358 is awaiting action (not merged or closed).