SolidStart "server$ cannot be used" boundary error in CI

SolidStart splits server functions (marked "use server") into a server-only bundle at build time. If one is declared or called where the compiler cannot create the boundary, or it references client-only values, the build errors.

What this error means

The build fails with a message that a server function cannot be used in this context, or that a "use server" directive is misplaced, pointing at the call site.

vinxi

Error: "use server" functions can only be defined at the top level of a
module or inside a component, not inside a conditional.
  at src/routes/api.ts:8

Common causes

A server function declared in an unsupported spot

Placing "use server" inside a conditional or a non-top-level closure prevents the compiler from extracting the boundary.

Client-only values captured by the server function

A server function that closes over browser objects cannot be serialized to run on the server.

How to fix it

Declare server functions at a supported level

Move "use server" to the top of the function body, at module top level or inside a component.
Pass only serializable arguments; do not capture DOM objects.
Re-run the build to confirm the boundary is created.

src/routes/user.tsx

async function loadUser(id: string) {
  "use server";
  return db.users.find(id);
}

Keep server and client data separate

Return plain serializable data from server functions and use it on the client, rather than passing client objects in.

How to prevent it

Declare "use server" only at the top of a function, not in conditionals.
Pass and return only serializable data across the boundary.
Keep browser-only values on the client side of the call.