feat(artifacts): add immutable artifact store

crates/crank-artifacts/src/error.rs

@@ -0,0 +1,23 @@
+use thiserror::Error;
+
+/// Stable, redacted failures from the artifact boundary.
+///
+/// This intentionally carries neither an operating-system source nor a path:
+/// those details belong only in the composing process's private logs.
+#[derive(Clone, Copy, Debug, Eq, Error, PartialEq)]
+pub enum ArtifactError {
+    #[error("artifact reference is invalid")]
+    InvalidReference,
+    #[error("artifact source is empty")]
+    EmptySource,
+    #[error("artifact source exceeds the configured maximum")]
+    SourceTooLarge,
+    #[error("artifact was not found")]
+    NotFound,
+    #[error("artifact integrity verification failed")]
+    Integrity,
+    #[error("artifact storage root or entry is unsafe")]
+    UnsafeRoot,
+    #[error("artifact storage is unavailable")]
+    Storage,
+}