Function plan_inline_function 

pub fn plan_inline_function(
    _ctx: &RefactoringContext,
    file_abs: &Path,
    content: &str,
    line: usize,
    col: usize,
    force: bool,
) -> Result<InlineFunctionOutcome, String>

Build an inline-function plan without touching the filesystem.

file_path is the path of the file (absolute or relative; used for grammar detection and error messages). content is the file’s current text. line and col are 1-based and point to the function name — either in the definition or at a call site. force overrides the single-use check.