docs(materialized_artifact): drop artifact! macro doc; restore ENV_PREFIX doc

Author: claude

crates/materialized_artifact/src/lib.rs

@@ -42,9 +42,6 @@ pub struct Artifact {
     hash: &'static str,
 }
 
-/// Construct an [`Artifact`] from the env vars published by a build script
-/// via `materialized_artifact_build::register`. Must match the `ENV_PREFIX`
-/// constant in `materialized_artifact_build`.
 #[macro_export]
 macro_rules! artifact {
     ($name:literal) => {

crates/materialized_artifact_build/src/lib.rs

@@ -1,5 +1,8 @@
 use std::{fs, path::Path};
 
+/// Namespace prefix for the env vars set by [`register`] and consumed by
+/// `materialized_artifact`'s `artifact!` macro. Exported so both crates agree
+/// on the same prefix.
 pub const ENV_PREFIX: &str = "MATERIALIZED_ARTIFACT_";
 
 /// Publish an artifact at `path` so `materialized_artifact`'s `artifact!($name)`