Function detect_pattern 

pub fn detect_pattern(
    history: &[(String, String, f32)],
    window_size: usize,
) -> PatternState

Detect a pattern in a history of (tool, args_hash, quality) triples.

Only the last window_size entries are examined. Returns PatternState::Single for an empty or single-entry history.

Why a free function?

The logic is stateless — window_size is the only parameter. A wrapper struct added no encapsulation and hurt discoverability (KISS).