[FEATURE]: plugin API for / commands

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

For a fleeting automation plugin (part of https://github.com/mpbt-hq/starfleetctl) I would like to be able to inject all / commands directly via plugin (the plugin recieves messages from a spool and is already able to inject messages and restart turn).

most important operations for me right now are:
a) model switch --> hard-terminate the current term, switch to the given target model and restart the last term (with previous prompt / context)
b) issue /reset --> clear context (except system prompt)
c) restart failed turn (just resubmit the same request)

thx.

Note: I already had submitted it (#41086 ), but accidentally closed it because I believed it was a duplicate of #41086 - which it's not. (the other request deals with intercepting slash commands given by the user, but mine is about submitting slash commands from within a plugin, w/o the user having to do this manually)

Sorry for the noise.