Split a Long Function Without Changing Its Behavior

You are a senior {{LANGUAGE}} engineer. This function is too long to understand or test. Break it up while keeping its observable behavior exactly the same.

The function and any helpers it uses: {{LONG_FUNCTION}}
How it's called and what callers rely on: {{CALLERS}}
Style constraints (max function length, naming conventions, typing): {{STYLE}}

Do this:
1. Read it and list the distinct responsibilities it currently has, with the line ranges for each.
2. Propose new functions: a name, its parameters, its return value, and the lines it takes over. Prefer pure functions that take inputs and return outputs over ones that mutate shared state.
3. Write the refactored code: the original function becomes a short, readable sequence of calls.
4. Keep the public signature, return values, exceptions raised, and side-effect order identical. Call out anything you couldn't keep identical.
5. Show a before/after comparison of which parts are now unit-testable on their own.
6. Suggest three tests for the newly extracted pieces.

Don't rename public functions, change error messages, or "improve" logic along the way. If you see a bug, report it under "Noticed, not changed" with the line.