diff --git a/adk-rust/crates/detmir-portal/src/production/health.rs b/adk-rust/crates/detmir-portal/src/production/health.rs
index ddddfd9..8a87de6 100644
--- a/adk-rust/crates/detmir-portal/src/production/health.rs
+++ b/adk-rust/crates/detmir-portal/src/production/health.rs
@@ -1,3 +1,8 @@
+//! Liveness probe payload.
+//!
+//! CONTRACT: `/healthz` is intentionally shallow. It proves that the portal
+//! process can answer HTTP, while dependency checks belong to `/readyz`.
+
 use serde_json::{Value, json};
 
 use crate::now;