#469: Preserve hash additions in place

[akmhatey-ai]

Fixes #469.

Fbe.overwrite already updates scalar-form absent properties on the existing fact. The hash form did not have the same absent-property path, so adding { bar: 44 } destroyed and reinserted the fact even when all requested properties were missing.

This change keeps the destroy/reinsert path for existing-property hash updates, but assigns the all-absent hash properties directly on the current fact. The regression test pins that identity-preserving behavior with Factbase::Pre.

Validation:

• ruby -c lib/fbe/overwrite.rb -> Syntax OK
• ruby -c test/fbe/test_overwrite.rb -> Syntax OK
• origin/master manual repro -> PASS origin/master reproduces issue: before pos=0, after pos=1
• candidate manual repro -> PASS hash absent property preserved pos=0, foo=42, bar=44
• existing-property hash path repro -> PASS existing-property hash path recreated pos=1, foo=55, bar=44, keep=yes
• git diff --check origin/master...HEAD -> no output
• git diff origin/master...HEAD -- lib/fbe/overwrite.rb test/fbe/test_overwrite.rb | gitleaks stdin --no-banner --redact -> no leaks found
• GitHub Actions on this PR are green: actionlint, copyrights, markdown-lint, pdd, rake on Ubuntu/macOS Ruby 3.3, reuse, typos, xcop, and yamllint.

Limitations:

• bundle exec ruby -Itest test/fbe/test_overwrite.rb and bundle exec rubocop lib/fbe/overwrite.rb test/fbe/test_overwrite.rb were blocked in this Windows environment because Bundler was missing locked gems (rdoc 7.2.0, psych 5.3.1, parallel 2.0.1), and installing psych 5.3.1 failed due missing yaml.h / MSYS2 keyring errors.
• non-bundled rubocop lib/fbe/overwrite.rb test/fbe/test_overwrite.rb reported one unchanged pre-existing warning at test/fbe/test_overwrite.rb:16 for Lint/RedundantCopDisableDirective.

[GHX5T-SOL]

Approved current head 1f43d72.

The patch matches #469: hash-form updates where every requested key is absent now assign onto the existing fact, mirroring the scalar absent-property path, while existing-property hash updates still take the delete/reinsert path. The new Factbase::Pre regression proves the absent-property hash case keeps the original pre-inserted position, so it catches the identity-changing behavior from the report.

Validation I ran locally on Ruby 3.3.11:

• bundle install with BUNDLE_PATH=/private/tmp/bundle-fbe-491
• bundle exec ruby -Itest test/fbe/test_overwrite.rb -- --no-cov -> 28 tests, 57 assertions, 0 failures
• bundle exec rubocop lib/fbe/overwrite.rb test/fbe/test_overwrite.rb -> 2 files inspected, no offenses
• ruby -c lib/fbe/overwrite.rb and ruby -c test/fbe/test_overwrite.rb -> Syntax OK
• bundle exec rake test -> 284 tests, 803 assertions, 0 failures, 9 skips
• git diff --check origin/master...HEAD -> clean
• diff-only gitleaks on lib/fbe/overwrite.rb and test/fbe/test_overwrite.rb -> clean

Hosted checks are also green, including Ubuntu/macOS rake.

[0crat]

@GHX5T-SOL Thanks for the review! You've earned +10 points for this contribution: +18 as a basis, -8 for absolutely no comments posted during the review. Your running score is +416; don't forget to check your Zerocracy account too.

[yegor256]

@akmhatey-ai merge conflict here

[yegor256]

Please fix the merge conflicts so this pull request can be merged.