Args become the PROGRAM's argv, never the compiler's. For the compiled languages the toolchain builds first and these are passed to the binary it produced.
Code is the WHOLE program, not a fragment: it is written to a single file and that file is what runs, so a compiled language needs its entry point and an interpreted one runs top to bottom.
Files are inputs the host already put in some session. Each names the session its bytes live in, which is usually — and ideally — the session this run wants.
Lang selects the toolchain, and with it the filename the code is written to and the line that runs it: py, js, ts, bash, r, php, go, rs, c, cpp, java, d, f90. Anything else is refused rather than guessed at — a run in the wrong language fails somewhere deep in a compiler, which reads as an outage.
RuntimeSessionHint is the stateful-session hint. It is carried so a client that sends it is not silently misread, and it selects nothing here: every session in this implementation is already a warm sandbox, so there is no second kind of runtime for a hint to choose between.
SessionID continues an EXISTING sandbox, which is what makes runs stateful: the same filesystem, so one run's output file is the next run's input. Empty leases a fresh sandbox and the id it got comes back on the result.
UserID attributes the run inside the caller's org. It is a label, never a tenant: the org is resolved from the validated principal and a value here cannot widen what the run may reach.
