[yeongseon]

Summary

Move OpenAPI schema-version conversion into a private module to separate conversion logic from specification assembly.

Changes

• Move nullable-reference handling, inline and component schema conversion, and the OpenAPI 3.0 compatibility check into _schema_version_conversion.py.
• Keep compatibility re-exports in spec.py and preserve the existing conversion algorithms, warnings, exceptions, and public behavior.
• Preserve distinct inline/component conversion passes, recursion handling, and final-document validation.
• Update DESIGN.md. Existing tests and assertions remain unchanged.

Validation

• make test: 1,633 passed, 30 skipped, 22 deselected; coverage was 95.22% before and 95.25% after the extraction.
• make format-check, make lint, make typecheck, make build, make perf, make lint-workflows, and make security passed.
• make check-all was not run as a single command; its constituent checks were run individually. Cloud validation was not run.
• Local performance budgets passed before and after. Median results (10/50/200/500 operations) were 79.93/418.49/1598.60/4454.99 ms before and 82.07/407.62/1645.02/3435.57 ms after; these measurements do not establish a performance improvement.
• Editor LSP could not resolve Hatch imports; strict repository mypy passed. Maintainer review of the final stacked changes remains pending.

Related Issues

Refs #819

Final PR of the five-part series. Stacked on #841 → #840 → #838; #839 is an independent cleanup. Merge prerequisites first and close #819 after the entire series is merged.

[Copilot]

🔵 Needs a closer look

Current-head maintainer authorization for the policy-bearing design update remains outstanding, and the merge checklist is incomplete.

No open issues 🎉

What changed in this PR

This final extraction PR for #819 separates schema version conversion from document compilation, preserving existing conversion behavior and diagnostic ordering.

Changes:

• Move recursive conversion, inline-schema traversal, and residual OpenAPI 3.0 compatibility checks into one private module.
• Retain compatibility re-exports in spec.py, leaving existing tests and assertions unchanged.
• Document the final compilation sequence and why each conversion pass remains necessary.

File	Description
src/​azure_functions_openapi/​spec.py	Replace conversion implementations with compatibility re-exports.
src/​azure_functions_openapi/​_schema_version_conversion.py	Isolate the existing conversion family without registry or CLI dependencies.
DESIGN.md	Explain the conversion boundary, pass ordering, and retained work.

_{Review effort: Balanced}