rstudio-server: rpm install failure is masked by `|| true`, then `start` fails

[scttfrdmn]

Found while smoke-testing the checksum-manifest work (spawn#419, real t3.small install of rstudio-server@v1.0.1).

Symptom

spawn plugin install rstudio-server@v1.0.1 reaches the instance, runs install steps, then fails at the start step:

start: step[0] type=run: run "systemctl enable --now rstudio-server\n": exit status 1
Unit rstudio-server.service could not be found.

On the instance afterward: package rstudio-server is not installed.

Root cause

The "Install RStudio Server" step (plugins/rstudio-server/plugin.yaml) ends the rpm/deb install with || true:

dnf install -y rstudio-server-*.rpm 2>/dev/null || \
  dpkg -i rstudio-server-*.deb 2>/dev/null || true

So if the download/install fails (here the RSTUDIO_VER lookup curls .../rhel9/x86_64/VERSION and the rpm URL likely 404s / the glob matches nothing), the step still "succeeds", and the later start step (systemctl enable --now rstudio-server) fails because the package was never installed.

Suggested fix

• Don't mask the failure with || true; fail the install step if neither dnf install nor dpkg -i succeeds.
• Verify RSTUDIO_VER is non-empty and the downloaded artifact exists before installing; the VERSION endpoint is hard-coded to rhel9/x86_64 even on arm64.
• Consider a health/post-install assertion that rstudio-server is installed before the start phase.

Not a supply-chain issue — orthogonal to spore-plugins#8. Filing so the integration path actually goes green.