LinardsLiepenieks Before planning, scope the codebase. Trace the import graph around where the change will live (the files it'll touch and, one hop out, their neighbors) to pin down roughly where it belongs and what it connects to. Flag anything that should reshape the plan.
Then plan relentlessly until you and the user reach a shared understanding. Walk each branch of the decision tree, resolving dependencies between decisions one at a time. Ask one question at a time, each with your recommended answer. If a question can be answered by exploring the codebase, explore instead of asking.