Startup: "Forget" unused interpreters, or otherwise start them up less aggressively

[jmcphers]

Feedback from @nealrichardson:

I am working on an R package in Positron. There's no Python code in this directory anywhere, it's very clearly an R package. But when I open it in Positron, the Console tab is showing a Python interpreter running. I'm all for being Python first and all, but this seems excessive :)
Just to be sure, I just installed the latest Positron prerelease, and watched closely as the project opened. First it opened the Python repl, then it switched to the R console, and then after another little while, it switched back to Python

via https://positpbc.slack.com/archives/C05M2EZCPGR/p1716471902486219

This is emergent behavior resulting from two different Positron behaviors.

• Python is started if nothing else seems appropriate (this probably happened at one point in the past in Neal's project)
• We remember what was started and always start it again until you shut it down manually at some point

Both were intentional, but this emergent behavior isn't. We could help cut the chatter by:

• automatically un-affiliating runtimes that don't actually get used (when there is a runtime that does get used), and/or
• not creating an affiliation for a runtime that was only a guess

(Note that the switch-back-and-forth issue at startup is tracked separately, in #1143)

[jthomasmock]

Somewhat related I think is: #4011 -- Sharon has a good suggestion there:

Perhaps a future enhancement to the new project flow is to ask the runtime service to make interpreter discovery of other languages opt-in. For example, for an R Project created via the Project Wizard, we wouldn't do Python interpreter discovery unless the user deliberately asks for Python interpreters through some UI affordance. Another thought is that we could ask the language extensions to do discovery "quietly" and not show notifications/errors unless the user is actively using that language.

[jmcphers]

First it opened the Python repl, then it switched to the R console, and then after another little while, it switched back to Python

This particular annoyance is addressed in #5959 (i.e. you should no longer see Python opening/starting in your R project unless you used it recently). This issue can now track the work to forget Python entirely if it is not used.

[testlabauto]

Verified Fixed

Positron Version(s) : 2025.02.0-59
OS Version          : OSX

Test scenario(s)

Opened r_testing subproject of qa-example-content many times and the previously selected version of R became active each time.

Link(s) to TestRail test cases run or created: