Say the boundary in operational terms
Name the contact, behavior, topic, access, or commitment you will and will not participate in. For a message about how to resolve conflict over the tone of feedback, use this factual base: identify the task, decision, deadline, role, or resource and use dated examples of the impact.
Define any necessary exception
If an exception is necessary, give it one purpose, one channel, and a clear limit. Propose an owner, working rule, or decision route and set a short review point. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Respond to escalation safely
Do not retaliate, gossip, conceal risk, or turn a process disagreement into a personal accusation. Use HR, a representative, security, or legal support for discrimination, harassment, threats, retaliation, or unsafe work. You do not need the other person to agree with a boundary for you to follow it consistently.