By default starkits are read-only. You must give the -writeable flag to sdx when doing the wrap for your starkit to be writeable.
You make your starkit writable by doing it at wrap time:
sdx wrap app.kit -writable
[Insert a stand alone example script to add and perhaps update files within app.kit.]
"-writable" Starkits automatically commit changes every 5 seconds.
05Feb03 Jeff Smith - "HeadsUp" [L1 ] is an example of single-file website - i.e. tclhttpd wrapped up as starkit, with user data inside.