Added Appbundler support in linux hab pkg

[sanghinitin]

Summary

Replaces the hand-rolled wrap_ruby_knife / wrap_bin_with_ruby pattern in habitat/plan.sh with the standard appbundler gem approach, following the same patterns adopted in This will also fix https://progresssoftware.atlassian.net/browse/CHEF-33638

What changed and why

• Switched binstub strategy from wrap_bin_with_ruby to appbundler – The old wrapper hardcoded a gem path that could drift as gem versions changed and did not pin dependency versions at startup. Appbundler reads Gemfile.lock and emits gem "name", "= VERSION" activation calls for every pinned dep, eliminating "ambiguous specs" warnings and ensuring reproducible load-time behaviour.
• Added binstub_patch.rb – Injected into every appbundler-generated binstub via sed at build time. Sets APPBUNDLER_ALLOW_RVM=true (prevents appbundler from clearing the carefully constructed Habitat runtime GEM_PATH) and prepends the vendor path so the binstub is runnable directly without the wrapper.
• Dual-store GEM_HOME / GEM_PATH layout – bundle install (with --local path vendor/) places Gemfile deps under vendor/ruby/3.4.0/ (bundler subdirectory); gem install knife-*.gem with --ignore-dependencies places knife itself under vendor/ (flat GEM_HOME). The libexec wrapper sets GEM_HOME=vendor/ruby/3.4.0 and GEM_PATH=vendor/ so both stores are visible.
• Added lifecycle hooks – do_prepare (creates /usr/bin/env symlink), do_after (removes .github/ dirs from vendored gems), do_strip (no-op to prevent Habitat stripping Ruby binaries), do_end (cleans up symlink).
• Simplified Habitat CI test helper – Removed version-pinned installer and verbose debug logging from artifact.habitat.test.ps1; now uses the always-latest standard install script.

Files / paths touched

• habitat/plan.sh – Complete rework of do_setup_environment, do_install; removed wrap_ruby_knife / wrap_bin_with_ruby; added appbundler workflow with libexec wrapper; added core/sed to build deps; added do_prepare, do_after, do_strip, do_end.
• binstub_patch.rb – New file at repo root; patched into binstubs by do_install.
• .expeditor/buildkite/artifact.habitat.test.ps1 – Simplified Install-Habitat function; removed $HabitatVersion pin; removed verbose debug logging.

Evidence

Before / After

Aspect	Before	After
Binstub strategy	Custom wrap_bin_with_ruby bash wrapper with hardcoded $GEM_PATH	Appbundler-generated binstub with per-dep gem "x","= VERSION" activation + libexec wrapper
Dep version pinning	None – any version in GEM_PATH resolved at runtime	Exact Gemfile.lock versions activated by appbundler before Kernel.load
Ambiguous-specs warning	Possible when multiple versions present	Eliminated via --ignore-dependencies + dual-store separation
Dynamic plugin loading	Relied on $HOME/.hab/knife/ruby/ (unresolvable in Habitat context)	Supported by appbundler open-gemset design; APPBUNDLER_ALLOW_RVM=true preserves GEM_PATH

Tests / logs

Command : bundle exec rspec spec/unit/
Result  : 1339 examples, 0 failures, 2 pending
Pending : 2 pre-existing expected-pending examples (color terminal + lazy-load isolation)
Duration: 5.01 seconds (load: 17.13 s)

Delegation checklist

Risk & Rollback

• Risk: Low — build-time change only; knife functional behaviour is unchanged. Appbundler is already the standard pattern across Chef ecosystem projects.
• Rollback: revert commit 11857c2

git revert 11857c2 --no-edit
git push origin main