Chatlio

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Build me a chat widget that answers into my team's chat, replacing Chatlio.

The idea is that support lives where the team already is. That means a relay: a visitor types on your site, the message appears in a channel, somebody replies there, and it goes back. Everything below serves that round trip.

STACK
- Node 20+ with Fastify
- SQLite through better-sqlite3, WAL mode
- One embeddable widget under 15KB gzipped, from your own domain
- One chat platform adapter to begin with
- Caddy in front

THE DATA MODEL
- conversations: id, visitor_id, channel_ref, thread_ref, status, page_url, referrer, started_at, last_message_at, closed_at
- messages: id, conversation_id, direction, author_name, body, external_id, created_at
- visitors: id, visitor_hash, name, email, traits_json, first_seen_at, last_seen_at
- page_views: id, visitor_id, path, title, at — the trail, which is the context that makes a reply useful
- The thread reference is how a reply in the channel finds its way back. Store it on the first message and never lose it

THE ROUND TRIP
- A new conversation opens a thread in the channel with the visitor's page, referrer and recent trail in the first message
- Every visitor message is posted into that thread
- Every reply in the thread that is not from the bot goes back to the visitor. Filter on the author, and never echo your own messages, which is the loop this design invites
- Idempotency by the platform's message id, so a redelivered event does not double-post
- The platform's rate limits respected with backoff

THE WIDGET
- One script, one init call, optionally with a signed identity token from your product so a known user is not asked who they are
- Delivery by polling a small endpoint with a backoff — faster while a conversation is active, slower when idle. Sockets are the obvious answer and the wrong first one
- Shadow DOM so your page's styles and the widget's cannot reach each other; keyboard operable, focus trapped, Escape closes, usable at 320px
- **Offline honesty**: when nobody is available it says so and takes an email address rather than pretending somebody is there. A widget that looks instant at midnight is the thing that annoys people most
- History for an identified visitor, so nobody starts again on every page

WHAT THE AGENT SEES
- The page they are on, the referrer, the pages before it, the device and the country. That context is most of what makes a fast reply possible
- Canned replies by shortcut, expanded in the channel
- Commands in the thread to close, assign or tag, so nobody leaves the chat window

OPERATIONS
- .env: DATABASE_PATH, BASE_URL, PLATFORM_TOKEN, SIGNING_SECRET, WIDGET_JWT_SECRET, HASH_SALT, ALLOWED_ORIGINS
- Migrations on boot, each once; events received by webhook with signature verification
- Nightly backup off the machine, restore script
- Health endpoint that posts and deletes a message in a test channel

WHAT MATTERS MOST
The thread reference and the echo filter. Build the round trip first and talk to yourself through it for a day — a relay that loops, or that loses which thread belongs to which visitor, is unusable immediately.