[benjaminguttmann-avtq]

Add the mapping from JRuby to Ruby, so we are able to introduce new JRuby Versions:

https://www.jruby.org/download

JRuby 10.x requires Java 21+, but the recipe always used the stack's
JDK 8 and a pinned Maven 3.6.3, so builds for the newly mapped 10.0/10.1
versions would fail at compile time.

• Select JDK and Maven per JRuby major version (jrubyToolchainFor):
  9.x keeps JDK 8 + Maven 3.6.3, 10.x uses JDK 21 + Maven 3.9.9
• Add bootstrap.jruby_jdk21 to cflinuxfs4/cflinuxfs5 stack YAMLs and
  BootstrapConfig.JRubyJDK21 (installs to /opt/java21)
• Derive the "supported prefixes" error message from the version map
• Add tests for 10.0 -> 3.4, 10.1 -> 4.0, per-major toolchain selection
  and the JDK 21 stack config

[Copilot]

🟡 Changes recommended

The newly accepted JRuby 10.x versions cannot compile because the build still selects JDK 8 rather than the required Java 21 or later.

1 open issue

• JRuby 10.x requires Java 21, but stacks still configure JDK 8 · New

What changed in this PR

Extends the binary builder’s JRuby-to-Ruby compatibility mapping to recognize newer JRuby series.

Changes:

• Maps JRuby 10.0 to Ruby 3.4 and JRuby 10.1 to Ruby 4.0.
• Preserves the existing JRuby 9.3 and 9.4 mappings.

File	Description
internal/​recipe/​jruby.go	Adds compatibility mappings for JRuby 10.0 and 10.1.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Mocked downloads and command execution cannot verify the JDK 21 bootstrap checksum or establish JRuby 10.0/10.1 build and runtime compatibility, leaving real Docker/network validation on both stacks outstanding.

No open issues 🎉

1 resolved since last review

• JRuby 10.x requires Java 21, but stacks still configure JDK 8

_{Review effort: Balanced}