Preserve cached asset ownership while expanding paths

[OskarEichler]

Summary

Loading a cached asset expands its paths on a copy, preserving reusable cache entries across application roots.

The loader previously expanded path fields directly in objects retained by shared in-memory caches. Copy the asset and metadata hashes before existing per-array expansion. Verified four roots with Hash, MemoryStore and FileStore, including linked/included assets. This does not promise deep isolation for arbitrary application metadata.

Reproduction

With require "sprockets"; require "tmpdir":

Dir.mktmpdir do |dir|
  cache = {}
  envs = %w[first second].map do |name|
    root = File.join(dir,name); Dir.mkdir(root)
    file = File.join(root,"entry.js")
    File.write(file,"var value=1;"); File.utime(1700000000,1700000000,file)
    env = Sprockets::Environment.new(root); env.append_path(root); env.cache = cache
    env
  end
  [0,0,1].each do |i|
    p envs[i]["entry.js"].filename.start_with?(envs[i].root + "/")
  end
  # true, true, true; previously the third read is false and retains the first root.
end

Verification

• Isolated patch and release baseline: unchanged bundle exec rake test, 913 tests /4,109 assertions /zero failures/errors /four skips, Ruby 3.2.11 and 4.0.6. 162 focused external checks for this patch on each Ruby.
• Eight follow-ups combined with existing Use Ruby 3 keyword argument handling for find_asset! #792: same suite plus 1,540 focused checks per Ruby. Combined isolated test task also passes. Full RuboCop passes all 133 files; Ruby syntax and diff whitespace checks pass.
• Gem build preserves 84 file paths, version 4.4.1, Ruby >=2.5 and dependency metadata. Consumer based on installed release/current main 49d9f20c00ac7d9a7ee57db058961edcccd86699, without unrelated upgrades.
• Existing asset-clean test is timing-sensitive: touching its fixture within the current timestamp second reproduced the same line-80 assertion failure on baseline and an independent cache patch (2/4 each). Full successful runs above are actual runs; no test code was changed. Normal skips cover legacy Ruby, Windows and two Sass cases; non-terminal stdin adds the Unix-device skip.

Compatibility and limitations

Breaking changes: no intentional change to valid supported behavior; the incorrect behavior above changes. No new dependencies or version upgrades. Older Ruby/Linux/JRuby checks are left to upstream CI, not claimed locally. No tests added/edited under the consumer repository's no-test-edit policy; focused evidence was run externally. Prepared with AI assistance. This is a focused correction, not an exhaustive Sprockets review.