Make scala-cli repository configuration a single source of truth (including Bloop bootstrap)

[ghostbuster91]

Is your feature request related to a problem? Please describe.
Recently there was a Bloop issue where it tried to bootstrap itself from Sonatype snapshots, and the snapshot repository was unavailable / broken: scalacenter/bloop#2870

In corporate environments we rely on internal artifact mirrors/proxies to avoid issues with public infrastructure and to ensure reproducible, policy-compliant builds (network egress restrictions, auditing, caching, etc.).

We configure scala-cli to use our internal mirror, e.g.:

scala-cli --power config repositories.default $REPO_URL/maven

This should configure the whole dependency resolution stack that scala-cli relies on.

We go a step further and set also:

COURSIER_REPOSITORIES=$REPO_URL/maven

However, despite both of the above, in our case Bloop still attempted to download artifacts from oss.sonatype.org during bootstrap. This makes scala-cli builds unreliable and it defeats the purpose of central repository configuration.

Describe the solution you'd like
Provide a simple and consistent way to configure repositories used by scala-cli and all tools/components it invokes (including Bloop bootstrap), such that:

• Setting repositories.default (or any related scala-cli option) becomes a single source of truth for repository configuration across the entire stack.
• Include an option/behavior like "no default repositories" (e.g. --no-default-repositories or similar), so corporate setups can guarantee zero external repo access.

Describe alternatives you've considered

For now we just disabled bloop in scala-cli via server=false.

[tgodzik]

Thanks for reporting! One important mention is that it was actually Scala CLI downloading Bloop, Bloop itself was not doing anything here.

The new release 1.12.2, has the snapshot repositories removed, but I think we should take into account the user defined repositories first.