BusinessException (and its subclass LeauditException) had no
FastAPI exception handler, so they escaped as unhandled 500s
even when carrying the correct status code (e.g. 403). Add a
handler that renders the status code and message as a proper
JSON response.
17-table PostgreSQL schema with full Chinese column comments,
FastAPI project structure (admin/common/modules),
DSL rule files, and schema migration scripts.
wren