[yeongseon]

Summary

Use diagnostics from each specification-generation call in reports and the CLI instead of rereading mutable registry state.

Changes

• Introduce an internal immutable generation result with its document, diagnostics, and validation metadata.
• Reuse pre-transformation validation when operation traversal is unchanged; validate the final document when method relocation or removal changes it.
• Preserve standalone warning collection, CLI mock-document compatibility, public interfaces, warning messages, and runtime serialization behavior.
• Add 19 regression cases for report isolation, validation ordering, CLI exit codes, custom operations, and runtime overhead.
• Update DESIGN.md with diagnostic ownership and the generation flow.

Validation

• make format-check, make lint, make typecheck, make test, make check-all, make build, and make perf passed.
• Final test suite: 1,633 passed, 30 skipped, 22 deselected, 95.22% coverage; existing expected warnings unchanged.
• Performance budgets passed at 10/50/200/500 operations; this PR did not measure a separate before/after speedup.
• Editor LSP diagnostics could not resolve some Hatch dependencies; repository strict mypy passed.

Related Issues

Refs #819

Stacked on #840, which is stacked on #838. Retarget and rebase after both prerequisite PRs merge; this is not the closing PR.

[Copilot]

🔵 Needs a closer look

The stacked refactor still needs integration review and authoritative final-head CI verification after its prerequisites merge and it is retargeted.

No open issues 🎉

What changed in this PR

This phase of #819 moves report and CLI diagnostics into an invocation-local generation result, reducing reliance on mutable registry state while preserving public APIs and compatibility publication.

Changes:

• Capture local diagnostics and reuse validation when operation traversal is unchanged.
• Update reports and the CLI to consume the result while preserving standalone collection and runtime serialization behavior.
• Add characterization tests and document diagnostic ownership and call flow.

File	Description
tests/​test_spec_report_local_diagnostics.py	Tests diagnostic isolation, validation counts, warning parity, and CLI behavior.
src/​azure_functions_openapi/​spec.py	Produces local generation results and conditionally reuses validation.
src/​azure_functions_openapi/​cli.py	Consumes local results while retaining plain-document compatibility.
src/​azure_functions_openapi/​_generation_result.py	Defines the internal frozen generation-result container.
DESIGN.md	Documents diagnostic ownership and before/after generation flow.

_{Review effort: Balanced}