Function handle_extract_function 

pub fn handle_extract_function(req: &RawRequest, ctx: &AppContext) -> Response

Handle an extract_function request.

Params:

• file (string, required) — target file path
• name (string, required) — name for the new function
• start_line (u32, required) — first line of the range to extract (1-based)
• end_line (u32, required) — last line (exclusive, 1-based) of the range to extract
• dry_run (bool, optional) — if true, return diff without writing

Returns on success: { file, name, parameters, return_type, extracted_range, call_site_range, syntax_valid, backup_id }

Error codes:

• unsupported_language — file is not TS/JS/TSX/Python
• this_reference_in_range — range contains this/self