Limits

The edge build is the Soli interpreter and the request pipeline, without the server around them. What needs a socket, a thread, a subprocess or a disk stays with soli serve.

Runs on the edge

Routes, controllers, before_action, middleware
Views, layouts, partials, components, view helpers
Query strings, URL-encoded forms, JSON bodies and responses
I18n from config/locales
SoliDB models over HTTPS: find, where, create, update…
The HTTP class, over the Worker's fetch
Static files from public/, served by Cloudflare

Stays with soli serve

WebSockets, LiveView, server-sent events and streamed bodies (answered with a 501)
Background jobs, cron, mailers that send
Multipart uploads and anything that writes files
PostgreSQL, MySQL, SQLite and the native SoliDB driver
--dev: hot reload, the dev bar, the REPL
PDF, Office documents, lossy WebP encoding, subprocesses

Worth knowing

One request at a time per isolate. A request suspended on a query keeps its isolate; Cloudflare spreads load over more isolates.
A Rust panic ends the isolate, where soli serve would answer a 500 and carry on. The next request boots a fresh one.
Size. About 3 MB compressed: inside the paid plan's limit, at the edge of the free one.
Sessions. The in-memory store lives as long as an isolate; use the cookie driver with SOLI_SESSION_SECRET.