Function thinking_level_for_budget 

pub fn thinking_level_for_budget(budget: u32) -> &'static str

Maps a raw thinking_budget value to the user-facing level name.

0 is the sentinel for “adaptive” (model decides). Positive values bucket into the four fixed tiers. Single source of truth — consumed by Runtime::thinking_level, the request builders in runtime/api.rs, and the status display.