Can a prompt replace Front?

Build a shared inbox whose defining property is that no message is ever in two states at once.

Stack: your choice, Postgres, Docker Compose. Receiving mail: use an inbound-email provider that posts a signed webhook, and verify that signature. Sending: SMTP through a transactional provider on a domain you own with SPF, DKIM and DMARC configured — document all three in the README, because without them your replies land in spam.

The state machine is the product. A Conversation has exactly one assignee (possibly nobody) and exactly one status from: open, snoozed until a timestamp, waiting on customer, closed. Every transition is written to an immutable log with who, when, from and to. Rules the code enforces:
- Sending a reply sets waiting-on-customer automatically.
- An inbound message on a waiting-on-customer or snoozed conversation reopens it and clears the snooze.
- Closing while unassigned is refused; you own what you close.

Internal comments are a separate entity from messages, stored in a different table, rendered in a visually distinct style, and — this is the safety property worth testing — the reply composer physically cannot include them. Write a test that asserts an outbound message body never contains comment text.

Assignment: assign to a person, or take it, with an optional round-robin over available people. An unassigned inbound conversation older than a configurable time appears in a "nobody owns this" list on the dashboard.

Threading by Message-ID, In-Reply-To and References, with a same-subject-and-participant fallback for clients that break references. Store raw MIME. Strip remote images and never auto-load them.

Canned replies with {{placeholder}} interpolation, and tags.

One report: median first-response time and median time to close, per week, computed from the transition log.

Write tests for every status transition rule above, for the internal-comment leak guard, and for the inbound webhook rejecting an unsigned request.

Do not build WhatsApp, SMS, or a mobile app. State in the README that these are the reasons someone keeps paying.