fix(gateway): stop candidate persistence retry storms

crates/aether-data/adapters/postgres/src/error.rs

@@ -1,7 +1,14 @@
 use crate::DataLayerError;
 
-pub(crate) fn postgres_error(error: impl std::fmt::Display) -> DataLayerError {
-    DataLayerError::postgres(error)
+pub(crate) fn postgres_error(error: sqlx::Error) -> DataLayerError {
+    let sqlstate = error
+        .as_database_error()
+        .and_then(|database_error| database_error.code())
+        .map(|code| code.into_owned());
+    match sqlstate {
+        Some(code) => DataLayerError::Postgres(format!("{error} (SQLSTATE {code})")),
+        None => DataLayerError::postgres(error),
+    }
 }
 
 pub(crate) trait SqlxResultExt<T> {
@@ -13,3 +20,67 @@ impl<T> SqlxResultExt<T> for Result<T, sqlx::Error> {
         self.map_err(postgres_error)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::postgres_error;
+    use sqlx::error::{DatabaseError, ErrorKind};
+    use std::borrow::Cow;
+    use std::error::Error;
+    use std::fmt::{Display, Formatter};
+
+    #[derive(Debug)]
+    struct TestDatabaseError;
+
+    impl Display for TestDatabaseError {
+        fn fmt(&self, formatter: &mut Formatter<'_>) -> std::fmt::Result {
+            formatter.write_str("unsupported Unicode escape sequence")
+        }
+    }
+
+    impl Error for TestDatabaseError {}
+
+    impl DatabaseError for TestDatabaseError {
+        fn message(&self) -> &str {
+            "unsupported Unicode escape sequence"
+        }
+
+        fn code(&self) -> Option<Cow<'_, str>> {
+            Some(Cow::Borrowed("22P05"))
+        }
+
+        fn as_error(&self) -> &(dyn Error + Send + Sync + 'static) {
+            self
+        }
+
+        fn as_error_mut(&mut self) -> &mut (dyn Error + Send + Sync + 'static) {
+            self
+        }
+
+        fn into_error(self: Box<Self>) -> Box<dyn Error + Send + Sync + 'static> {
+            self
+        }
+
+        fn kind(&self) -> ErrorKind {
+            ErrorKind::Other
+        }
+    }
+
+    #[test]
+    fn postgres_error_preserves_sqlstate_without_database_detail() {
+        let mapped = postgres_error(sqlx::Error::Database(Box::new(TestDatabaseError)));
+        assert_eq!(
+            mapped.to_string(),
+            "postgres error: error returned from database: unsupported Unicode escape sequence (SQLSTATE 22P05)"
+        );
+    }
+
+    #[test]
+    fn postgres_error_without_database_code_keeps_original_message() {
+        let mapped = postgres_error(sqlx::Error::PoolTimedOut);
+        assert_eq!(
+            mapped.to_string(),
+            "postgres error: pool timed out while waiting for an open connection"
+        );
+    }
+}