Look for recurring manual work
Repeated exceptions in permissions usually signal a missing model. Repeated plan changes signal entitlements. Repeated reporting requests signal an ownership gap. The pattern of manual work is a better guide than an architecture diagram alone.
Rank by risk and operating cost
Estimate the cost of leaving the boundary unresolved: support time, delayed sales, data corrections and engineering workarounds. Then compare that with the cost of building and operating the boundary. Start where the recurring cost is measurable and the change is bounded.
- Risk: what fails visibly or creates a data or support incident.
- Recurring cost: support hours, manual corrections and delayed revenue.
- Commercial constraint: a contract, compliance requirement or pricing commitment.
- Reversibility: whether the change can be bounded and undone.
Keep the next boundary explicit but unbuilt
Write down the boundary you are not building yet, the signal that would justify it and the decision owner. That keeps the architecture honest without paying for flexibility you cannot yet use.
Invest in the boundary that removes recurring manual work, not the one that looks most architectural.