It would help simplify the sjavac architecture to make it a thin client of a shared server.

Since it is not a design goal for the client to be able to access multiple servers, there is no need to put more work in the client than to locate the server and delegate the request to the server, This will simplify the protocol between client and server down to:
... send [current directory, args] to the server
... receive packets from server containing output for stdout/stderr, terminated by a packet containing the outcome (e.g. int return code)

With a thin client, it would also be easier to have sjavac support a "better javac" mode, in which the command line args are exactly those for javac, but which can be executed on the shared server. This mode would be an alternative to the current mode in which substantial analysis may be done to determine the minimum set of files to compile.