Why contextUser may not run sql on provider, or null when they may. The host checks the
SQL as it will run: one read statement, and every table it reads an entity view the user may
read in full.
The timeout, in seconds, to run with when the caller asks for requestedSeconds.
The host's checks for SQL a caller wrote, so that an action which runs such SQL applies the same rules as the host's own ad-hoc SQL API. MJServer registers one at startup.