There's a pattern that repeats reliably: a founder uses an agency to build the MVP, it ships, it works, and the engagement ends. Six months later the founder has a codebase they don't understand, no internal technical ownership, and a product that's hard to hand off to new engineers.
Here's the part that matters: the agency usually did nothing wrong. They did exactly what they were paid to do. The problem was structural, the engagement was scoped for delivery, not for handover. "Build us an MVP" produces an MVP. It doesn't produce the documentation, the context, or the transferable ownership that turns an MVP into something a company can carry forward. Those weren't in the contract, so they don't exist.
The founder discovers this at the worst possible moments. The first bug after the retainer ends. The first engineer interview where the candidate asks "why is it built this way?" and nobody knows. The first investor due-diligence pass that asks who owns the technical decisions. What looked like a finished product turns out to be a delivery with no institutional memory attached.
The fix isn't avoiding agencies, for many founders an agency is the right build option. The fix is scoping the engagement for what happens after it ends. Before signing, the contract should cover a handful of specific things.
Documentation as a deliverable, not a courtesy: architecture overview, setup instructions a new engineer can follow unaided, and an explanation of the data model. Decision records: every significant architectural choice, written down with the reasoning and the alternatives considered, because "why is it built this way?" will be asked, and the answer shouldn't leave when the agency does. Ownership hygiene - the founder holds the repositories, the cloud accounts, the domain, every credential, from day one, not transferred at the end. And a defined end-of-engagement phase: a real handover period, budgeted and scheduled, where the agency walks a nominated person, a new hire, a fractional CTO, even the founder, through the system while questions are still cheap to ask.
A healthy end of engagement looks unremarkable. A new engineer onboards from the documentation alone, the founder can answer diligence questions about their own product, and the agency is genuinely finished rather than perpetually on speed-dial.
Agencies scope what founders ask for. Founders keep what they remembered to ask for. The gap between those two is where MVPs quietly become liabilities.