I do automation work and recently solved an email problem for someone I work with. He was losing over an hour a day sorting his inbox and writing the same replies repeatedly. The system I built sorts mail into his own categories and pre-writes draft replies in his tone for him to review and send. It works for one person, and now I'm thinking through whether it's worth turning into a repeatable service. The challenge is the inbox-assistant space already has well-funded players. So my question is about methodology, not my specific thing: When you're entering a category that big incumbents already occupy, how do you validate that a narrower wedge (in my case, done-for-you setup and managing multiple inboxes for one person rather than a self-serve app) is actually defensible and not just wishful thinking? Specifically: How do you separate a real differentiator from cope before you sink months into building?…