Approval Process not retriggering after rejection when stage is manually changed back

We have an Approval Process on the Opportunities module that triggers when Stage is changed to Negotiation (Execute on: Edit Only). On rejection, a field update action reverts Stage back to Proposal.

The issue: after rejection, AE can manually changes Stage back to Negotiation (without resubmission), the Approval Process does not retrigger — the stage change goes through without requiring a new approval. This effectively allows AEs to bypass the approval gate after the first rejection.

We could lock Stage field after rejection but then AEs won't be able to set it to Closed Lost if needed.

Is there a way to make the Approval Process retrigger every time the Stage is set to Negotiation, regardless of previous approval cycles on the same record?