[codex] Fix relative URL refs with path-only root ids

[koxudaxi]

Summary

• resolve relative $id values against the retrieval URL before using them as the base for relative $ref resolution
• add resolver coverage for relative root $id plus base_url
• add a CLI regression test for --url input with path-only $id and relative external $ref

Root Cause

When a schema was fetched via --url and declared a path-only root $id like /schemas/v1/main.schema.json, that $id replaced the retrieval URL as the reference base without first being normalized to an absolute URL. The next relative $ref was therefore resolved as a local filesystem path instead of remaining remote.

Validation

• tox -e type
• tox -e readme
• tox -e cli-docs -- --check
• tox -e config-types -- --check
• tox -e py314-parallel -- tests/test_reference.py tests/main/jsonschema/test_main_jsonschema.py -k 'relative_root_id or root_id_differs_from_base_url or url_with_relative_root_id_resolves_relative_refs or root_id_jsonschema_with_remote_file or remote_ref'
• tox -e py312-parallel -- tests/test_reference.py tests/main/jsonschema/test_main_jsonschema.py -k 'relative_root_id or root_id_differs_from_base_url or url_with_relative_root_id_resolves_relative_refs or root_id_jsonschema_with_remote_file or remote_ref'

Fixes: #3080

[github-actions]

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[codspeed-hq]

Merging this PR will not alter performance

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✅ 11 untouched benchmarks
⏩ 98 skipped benchmarks¹

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_{Comparing codex/fix-relative-url-ref-3080 (dd04c13) with main (05901ff)}

Footnotes

1. 98 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (05901ff) to head (dd04c13).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main     #3084    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           87        87            
  Lines        18247     18633   +386     
  Branches      2087      2158    +71     
==========================================
+ Hits         18247     18633   +386     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[koxudaxi]

Superseded by #3085 due to branch and PR naming policy.