Adds RequestIX.use_case_inline so callers can define ad-hoc extraction
schemas in the request itself, bypassing the backend registry. The
pipeline builds a fresh (Request, Response) Pydantic class pair per
call via ix.use_cases.inline.build_use_case_classes; structural errors
(dup field, bad identifier, choices-on-non-str, empty fields) raise
IX_001_001 to match the registry-miss path. Inline wins when both
use_case and use_case_inline are set. Existing REST callers see no
behavioural change.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Dirk Riemann
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