contract/agreement_project/views/project_view.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <record id="edit_project_agreement" model="ir.ui.view">
        <field name="name">project.project.form.agreement</field>
        <field name="model">project.project</field>
        <field name="inherit_id" ref="project.edit_project"/>
        <field name="arch" type="xml">
            <field name="sequence" position="after">
                <field name="agreement_id"
                       domain="[('partner_id', '=', partner_id)]"/>
            </field>
        </field>
    </record>

</odoo>