Technical plan
Settle architecture once, separately from execution.
The pattern
Write the architecture down once, in one document, before execution starts. Name the stack, the boundaries, the data flow, and the things you decided not to build. The technical plan is where architecture gets settled. Everything after it is execution.
Why it matters more with an AI collaborator
An AI collaborator is persuasive, fast, and has no memory of last week. Left unanchored, it will happily redesign your system every session, and each redesign will sound reasonable. The plan is the anchor. When a proposal contradicts it, the plan wins by default, and changing the plan is a deliberate act, not a side effect of a good-sounding suggestion.
This is not about distrust. It is about asymmetry. You carry the context between sessions. The document is how you hand that context back.
The stability rule
The plan changes only by explicit decision, recorded in the decision log with a rationale and a reversal trigger. If a session ends with the architecture different from the plan, one of two things happened: the plan was updated on purpose, or the build drifted. The plan is what makes the difference visible.