The issue was caused by importing StreamingResponse and JSONResponse inside
the chat_completions function. In Python, when you have an import statement
anywhere inside a function, it creates a local variable for that name
throughout the entire function scope. This caused the code in the original
implementation path to fail because Python saw StreamingResponse as an
unassigned local variable.

Fix: Move StreamingResponse and JSONResponse imports to module level and
remove redundant imports from inside the function.