Function quality_signals_for_response 

pub fn quality_signals_for_response(
    response: &AgentResponse,
    max_iterations: usize,
) -> QualitySignals

Build heuristic quality signals from an agent response.

These signals stand in for the explicit reward signal used in ERL. Gestura does not have a verifiable task reward for most agent turns, so the runtime falls back to observable quality proxies such as tool errors, iteration pressure, truncation, and explicit failure language.