How bout restricting the dragging of stages per user? like

'draft to confirm' is for manager

'Approved to Rejected' is for general manager

You can take the reference of ECo, PLM enterprise module. The same thing can be done in that module.

Where can I see that?

If you have enterprise access then you can check module mrp_plm.. Where on every stages added responsible person who can validate, done that stage... You can also do the same in your case, on every stage add one2many of users and onchange of stage add constraint so only the responsible person can change the stage..