Sticky situation to be in when in a design-build relationship since you technically are working for the contractor. Glad to hear you have a BIM execution plan. For our office, once the BIM model is out of our custody, we do not take it back and claim it as our own. When we do provide the BIM model to someone, we have them sign a release. This is our template that we customize for each situation:

I know it may be too late to incorporate it for your current situation, but this might be good for future work with this DB partnership.
------------------------------
Bridgett Wakefield AIA
Reifsteck Wakefield Fanning & Company
Champaign IL
------------------------------
Original Message:
Sent: 05-02-2025 06:32 PM
From: Janene K. Christopher AIA
Subject: BIM Coordination Model and Design-Build
Our Design-Build partner is asking us to sign-off on the coordination model. The BIM execution plan already indicates the model coordination is the Trade Contractor's responsibility & they need to sign off. Anyone have any experience w/ this request. Seems they are treating this as a "submittal" rather than a coordination tool.
------------------------------
Janene Christopher AIA
Steinberg Hart
San Diego CA
------------------------------