docs: clarify hazard warns of UB risk that subsequent code must avoid

Author: hxuhack

pre-RFC.md

@@ -55,9 +55,10 @@ In contrast, **safety tags** represent safety properties using a formal language
 - `#[safety::requires(Prop1, Prop2, ...)]` — **preconditions**: safety requirements that must be
   satisfied before invoking an unsafe API. Most unsafe APIs carry at least one precondition.
   By default, every property in `requires` is a precondition. A property explicitly tagged with
-  `kind = "hazard"` instead denotes a temporary vulnerable state that deviates from Rust's safety
-  principles (e.g. [`String::as_bytes_mut`]). Hazards are informational and do not loosen the
-  mandatory preconditions.
+  `kind = "hazard"` instead warns of a risk that subsequent program execution must avoid triggering,
+  otherwise undefined behavior may occur (e.g. [`String::as_bytes_mut`] exposes a buffer that must
+  not be used to produce invalid UTF-8). Hazards complement preconditions but are not themselves
+  call-site obligations.
 - `#[safety::invariant(Prop)]` — **struct invariants**: properties that must hold for every instance
   of a struct at all observable points.
 - `#[safety::verify]` — marks a function as a verification entry point.