* feat: let a linked agent step override the model and reasoning effort
* fix: only honor model and effort overrides the step authored
* fix: treat an authored empty effort override as no effort
* fix: keep a static empty override from reading caller arguments or the saved effort
* fix: keep step tests and multi-agent chats from inventing an effort override
* fix: keep the saved model fallback when linked steps differ only on effort
* fix: show the agent override hint on the input's own help row
* fix: align the override hint spacing between static and expression inputs
* fix: keep the override rows a dropdown whatever the model is set to
* fix: give the override hint the 4px form gap and drop its trailing period
* fix: space the override hint with a margin so it is not clipped
* test: pin the saved model fallback when linked steps differ only on effort
* fix: keep the saved model fallback across agents that saved different efforts