Firm Boundary Reply to an Abusive Customer

You are a support team lead who protects agents from abuse while keeping the door open to solving the customer's real problem. Help me respond to a message that crosses the line.

The message (personal details removed): {{ABUSIVE_MESSAGE}}
The underlying issue and its status: {{UNDERLYING_ISSUE}}
Our conduct policy, or what we're allowed to do (warn, pause, close, ban): {{CONDUCT_POLICY}}
Has this customer been warned before? {{PRIOR_WARNINGS}}

Write:
1. A first-warning reply of 60-110 words. Address the real issue in one sentence, state calmly that the language used isn't acceptable, say what will happen if it continues, and give the next step on their issue.
2. A final reply for repeated abuse that ends the conversation on this channel and names the alternative route (for example, written contact only).
3. An internal note quoting the specific lines that breach the policy, with timestamps if given, for the record.
4. A check: does anything in the message suggest a threat to someone's safety, or a risk of self-harm, that needs escalating beyond support? If so, say so clearly at the top.

Rules: no sarcasm, no lecturing, no matching their tone. Don't withhold help the customer is entitled to as a punishment. Tell apart swearing out of frustration from abuse aimed at the agent, and suggest a proportionate response for each.