@headius — yes, we have tested this with JRuby.

Test environment: JRuby 10.1.0.0 (Ruby 4.0.0, Java 21, JLine 3.21.0, arm64-darwin)

Since this repo had no existing test infrastructure, we added the first test suite as part of this PR (test/test_history.rb) — 22 tests, 36 assertions, all passing. It covers the Readline::HISTORY API (push, pop, shift, set, delete_at, each, clear, size, empty?) and completion_proc, which is the surface area exercised by HBase shell via IRB.

A few notes on the migration:

• JLine 3's DefaultHistory does not expose remove(int) or set(int, String), so history mutation methods (pop, shift, delete_at, []=) are implemented via purge + rebuild — functional but not optimal. This is worth noting if the library stays in use.
• We re-added the ESC key → beep binding from JRUBY-852 using JLine 3's Widget interface.
• completion_append_character= is not supported by JLine 3 and now warns instead of silently no-oping.

We understand the project is moving toward reline. This PR is motivated by a CVE in jline 2.x (jline:jline) that affects HBase deployments today. Even as a transitional fix until jruby-readline is fully retired, we believe it's worth landing. Happy to address any concerns.