email.field_unused: Email's field is written by no template and no subject

Email's field is written by no template and no subject.

Area 16, Built-in services; declinable; the next step is usually the agent's.

An email's fields are what its templates and its subject read, so a field none of them reads is sent for nothing, or is a value a template meant to show. A judgement call: a decline line above the field keeps one deliberately:

example

/// Sent once someone signs up.type WelcomeEmail = EmailMessage {    name: Text    referral_code: Text}

jadpo checkcheck failed: 1 error, 3 files

error WelcomeEmail.referral_code is written nowhere

--> domains/accounts/emails/welcome_email.jadpo:4:5

  |4 |     referral_code: Text  |     ^^^^^^^^^^^^^ no template writes it

reason: An email's fields are what its templates and its subject read, so a field none of them reads is sent for nothing, or is a value a template was meant to show; no template of WelcomeEmail reads referral_code, and no wording of its subject writes {referral_code}.
next: Read referral_code in a template or the subject, or remove it from WelcomeEmail, or write decline email.field_unused: "<why>" above it if this is deliberate (agent)
rule: email.field_unused
help: https://jadpo.dev/docs/errors/email.field_unused