feat(poc): add terrors PoC crate scaffold and error types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/crates/arbiter-terrors-poc/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "arbiter-terrors-poc"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+terrors = "0.3"

server/crates/arbiter-terrors-poc/src/errors.rs

@@ -0,0 +1,84 @@
+use terrors::OneOf;
+
+// Wire boundary type — what would go into a proto response
+#[derive(Debug)]
+pub enum ProtoError {
+    NotRegistered,
+    InvalidSignature,
+    Internal(String),
+}
+
+// Internal terrors types
+pub struct NotRegistered;
+pub struct InvalidSignature;
+pub struct Internal(pub String);
+
+impl From<NotRegistered> for ProtoError {
+    fn from(_: NotRegistered) -> Self {
+        ProtoError::NotRegistered
+    }
+}
+
+impl From<InvalidSignature> for ProtoError {
+    fn from(_: InvalidSignature) -> Self {
+        ProtoError::InvalidSignature
+    }
+}
+
+impl From<Internal> for ProtoError {
+    fn from(e: Internal) -> Self {
+        ProtoError::Internal(e.0)
+    }
+}
+
+// Converts the narrowed remainder after handling NotRegistered
+impl From<OneOf<(InvalidSignature, Internal)>> for ProtoError {
+    fn from(e: OneOf<(InvalidSignature, Internal)>) -> Self {
+        match e.narrow::<InvalidSignature, _>() {
+            Ok(_) => ProtoError::InvalidSignature,
+            Err(e) => {
+                let Internal(msg) = e.take();
+                ProtoError::Internal(msg)
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn not_registered_converts_to_proto() {
+        let e: ProtoError = NotRegistered.into();
+        assert!(matches!(e, ProtoError::NotRegistered));
+    }
+
+    #[test]
+    fn invalid_signature_converts_to_proto() {
+        let e: ProtoError = InvalidSignature.into();
+        assert!(matches!(e, ProtoError::InvalidSignature));
+    }
+
+    #[test]
+    fn internal_converts_to_proto() {
+        let e: ProtoError = Internal("boom".into()).into();
+        assert!(matches!(e, ProtoError::Internal(msg) if msg == "boom"));
+    }
+
+    #[test]
+    fn one_of_remainder_converts_to_proto_invalid_signature() {
+        use terrors::OneOf;
+        let e: OneOf<(InvalidSignature, Internal)> = OneOf::new(InvalidSignature);
+        let proto = ProtoError::from(e);
+        assert!(matches!(proto, ProtoError::InvalidSignature));
+    }
+
+    #[test]
+    fn one_of_remainder_converts_to_proto_internal() {
+        use terrors::OneOf;
+        let e: OneOf<(InvalidSignature, Internal)> = OneOf::new(Internal("db fail".into()));
+        let proto = ProtoError::from(e);
+        assert!(matches!(proto, ProtoError::Internal(msg) if msg == "db fail"));
+    }
+}

server/crates/arbiter-terrors-poc/src/main.rs

@@ -0,0 +1,3 @@
+mod errors;
+
+fn main() {}