The seller contact came in on Friday and by Monday my partner had already called the title company without looping me in.

Your diagnosis is right. The title company contact point is a control mechanism, and whoever holds it shapes the information flow for the rest of the deal. The split line in most JV agreements gets negotiated carefully because it is visible. The closing coordinator role gets left out because neither party is thinking about it until the file moves and suddenly it matters.

The assumption doing the most work in the verbal-deal-by-deal approach is that both partners share the same definition of whose lane closing belongs to. They almost never do. One person thinks it follows the seller relationship. The other thinks it follows whoever is closer to the buyer. When nothing in the agreement resolves that, the Monday phone call resolves it instead, and not in a recoverable way.

A named closing coordinator clause is the cleaner structure. You define the role, you attach it to a trigger, your example of the executed seller contract is a clean one, and you specify what the non-coordinator partner receives and when: amendment notices, timeline updates, any request that affects the earnest money or close date. That gives the coordinator operational authority without making the other partner blind.

The risk you did not raise is what happens when the buyer wobbles and only one partner knows. If the coordinator is absorbing that information and making a call to extend or renegotiate without a defined notice obligation to the other partner, you have a 50/50 deal where one side is effectively running the back half solo. That is where splits start feeling wrong even when they are mathematically correct.

One thing to confirm with whoever drafted your agreement: whether your state treats the closing coordinator's communications as agency activity. Some do. That is a licensed professional question, not one to settle internally.

What did your partner's rationale turn out to be when you asked about the Monday call?

Nine doors in and we never wrote closing coordinator into a single one of our early JV agreements, and that cost us a relationship on a duplex in Slavic Village around 2021 where the other party had already negotiated a closing date change we didn't know about until the day before.

The 50/50 framing is where I'd push back a little. In my experience the split percentage actually does matter beyond optics, because whoever is closer to even tends to feel like they have equal standing to make unilateral calls, and that creates exactly the Monday-morning-title-call situation you're describing. On the lopsided deals we've done, like a 60/40 where one side clearly led, that person just assumed the closing coordinator role without anyone having to say it. The ambiguity lives loudest at 50/50.

What I'd actually want to know is whether your JV agreement specifies who holds the contract in their name with the title company, because that's a different and more concrete question than who "interfaces." Whoever is the named buyer or assignor on the contract is who the title company is going to call when something breaks, regardless of what the JV agreement says internally. Did you guys co-sign the purchase agreement or is one name on it?