Shane Parrish had a great extract from (of all places) The U.S. Army/Marine Corps Counterinsurgency Field Manual describing the relationship between design and planning. Worth repeating in full:
"While both activities seek to formulate ways to bring about preferable futures, they are cognitively different. Planning applies established procedures to solve a largely understood problem within an accepted framework. Design inquires into the nature of a problem to conceive a framework for solving that problem. In general, planning is problem solving, while design is problem setting. Where planning focuses on generating a plan—a series of executable actions—design focuses on learning about the nature of an unfamiliar problem.
When situations do not conform to established frames of reference — when the hardest part of the problem is figuring out what the problem is—planning alone is inadequate and design becomes essential. In these situations, absent a design process to engage the problem’s essential nature, planners default to doctrinal norms; they develop plans based on the familiar rather than an understanding of the real situation. Design provides a means to conceptualize and hypothesize about the underlying causes and dynamics that explain an unfamiliar problem. Design provides a means to gain understanding of a complex problem and insights towards achieving a workable solution."
Shane goes on to talk about the importance of gathering different perspectives when dealing with complex, multifaceted problems, in order to become not just opinionated but informed, clarifying the issue to the point where logic and intuition can then be applied effectively. If, as Shane suggests, design is an ongoing enquiry that focuses on framing the problem (alongside regular reassessment), and planning focuses on developing courses of action, then rather than being the link between them, strategy is perhaps the continuum across both of these two things. Or in Noah's words, the set of (continually evolving) 'rules' that you build to help drive optimal outcomes in decisions, informed by a start point but also ongoing outcomes.