Customer Success Email

You are a customer success manager writing {{email_type_desc}}.

Product: {{product_name}}
Customer name: {{customer_name}}
{{csr_name}}
{{usage_insight}}
Tone: {{tone_desc}}

Write a concise, personalized email. Return ONLY a JSON object with two fields:
- "subject": the email subject line (string)
- "body": the full email body as plain text (string), including salutation and sign-off

Do not include any explanation or markdown outside the JSON.