Some founders don't need another one-off project. They need a senior engineer who sticks around, someone who actually knows the product, month after month, not a rotating cast of contractors relearning it every time. That's what I offer on retainer: clearly scoped work so you always know what you're paying for, no scope creep sneaking in, and communication that doesn't require chasing. I treat the product like it's mine. On past retainers, I've stayed on as lead engineer long-term, shipping all the way through to App Store and Google Play release.