feat: only link roots into default view

[wdconinc]

Briefly, what does this PR introduce?

We keep hearing about many files from OSG folks. We have a symlink for all packages, even if we don't actually need to expose some of this functionality beyond explicitly included packages. This restricts what is linked into the view to only the roots.

I think we've tried this before. I forget why it failed. We'll see...

[Copilot]

Pull request overview

Updates the shared Spack environment view configuration to reduce the number of files exposed in the default /opt/local view by linking only environment root specs, aligning with the goal of minimizing unnecessary symlinks for downstream users (e.g., OSG).

Changes:

• Configure the default Spack view to link: roots (previously implicitly linking more than roots).
• Keep link_type: symlink and existing exclude/select behavior unchanged.

[wdconinc]

The problem here is that ROOT now cannot find headers like vdt/vdtMath.h since vdt is now not exposed in /opt/local anymore...

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

vdt is being added as an explicit root here to keep its headers present in the view for ROOT under link: roots, but other environments that also include root (e.g. cuda/, prod/, cvmfs/, jl/, tf/, ci_without_acts/) still don’t list vdt. If ROOT headers transitively include VDT headers, those envs will still have a broken /opt/local view for compilation. Consider adding vdt consistently wherever root is a root spec, or document why it’s only needed in xl/ci.

[Copilot]

This environment now explicitly adds root as a view root, but unlike xl/ci it doesn’t also add vdt (which those envs add to keep ROOT’s headers usable under link: roots). If ROOT’s public headers include VDT headers, compilation against ROOT via the view will fail here. Either add vdt as a root here too, or add a brief note explaining why TF doesn’t require it.

Suggested change

	- py-vector
	- py-vector
	- vdt

[wdconinc]

I've given up on making this work. It's a game of whack-a-mole to fix every new user-space issue that pops up.