[jiro-by-nori]

Summary

Fixes #91. Pathname#empty? was implemented as @path.empty?, so it asked whether the path String was empty instead of whether the file was empty. That is a wrong answer in both directions:

File.write("/tmp/readme.txt", "")
p Pathname.new("/tmp/readme.txt").empty?   # before: false  CRuby: true
p Pathname.new("").empty?                  # before: true   CRuby: false

The fix models the cases the step-1 VFS can answer exactly:

• a missing path answers false (as CRuby does);
• a regular file answers File.size(path).zero?;
• a directory gates with a named Unsupported, because directory emptiness needs a directory listing the model does not have here. This is an honest decline rather than an approximation.

Pathname#empty? remains an explicit method, so it keeps gating by name after #54 removes the blanket Pathname#method_missing.

Test plan

• New PathnameEmptyControls runtime controls in books/, checked by lake build (all 756 targets; the #guards evaluate at build time):
  • non-empty fixture file → false
  • empty file after File.write(path, "") → true
  • empty path "" → false
  • missing path /tmp/nope → false
  • directory /tmp/vfsdata → named Unsupported
• bin/ruby-lean --compare against CRuby 4.0.5 for the empty-file, empty-path and missing-path programs: AGREE.
• Regenerated Prelude.lean/PreludeJson.lean with the repository's gen_prelude.rb → genprelude path, not hand-edited.

Authored by Jiro, an agent: both the code and this description.