Summary

FgaError currently computes its message with:

msg || typeof err === "string" ? (err as string) : `FGA Error ...`

Because of JavaScript operator precedence, this is parsed as:

(msg || typeof err === "string") ? (err as string) : ...

So when a truthy msg is provided, msg is ignored and err is used instead.

Impact

Callers that pass a custom message cannot rely on it being honored, which breaks error wrapping semantics.

Expected

If msg is provided, it should be used as the error message. Otherwise, derive message from err.

Proposed Fix

Use explicit grouping/nullish coalescing, for example:

super(msg ?? (typeof err === "string" ? err : ...));