chore: move serde helpers to common utils

Relocate SurrealDB serde helpers out of storage types so they can be
reused broadly, and align retrieval-pipeline test setup with configured
embedding dimensions.

common/src/utils/mod.rs

@@ -1,4 +1,5 @@
 pub mod config;
 pub mod embedding;
 pub mod ingest_limits;
+pub mod serde_helpers;
 pub mod template_engine;

common/src/utils/serde_helpers.rs

@@ -0,0 +1,82 @@
+use chrono::{DateTime, Utc};
+use serde::de::{self, Visitor};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+use std::fmt;
+use surrealdb::sql::Thing;
+
+struct FlexibleIdVisitor;
+
+impl<'de> Visitor<'de> for FlexibleIdVisitor {
+    type Value = String;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string or a Thing")
+    }
+
+    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        Ok(value.to_string())
+    }
+
+    fn visit_string<E>(self, value: String) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        Ok(value)
+    }
+
+    fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
+    where
+        A: de::MapAccess<'de>,
+    {
+        let thing = Thing::deserialize(de::value::MapAccessDeserializer::new(map))?;
+        Ok(thing.id.to_raw())
+    }
+}
+
+pub fn deserialize_flexible_id<'de, D>(deserializer: D) -> Result<String, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    deserializer.deserialize_any(FlexibleIdVisitor)
+}
+
+pub fn serialize_datetime<S>(date: &DateTime<Utc>, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    Into::<surrealdb::sql::Datetime>::into(*date).serialize(serializer)
+}
+
+pub fn deserialize_datetime<'de, D>(deserializer: D) -> Result<DateTime<Utc>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let dt = surrealdb::sql::Datetime::deserialize(deserializer)?;
+    Ok(DateTime::<Utc>::from(dt))
+}
+
+pub fn serialize_option_datetime<S>(
+    date: &Option<DateTime<Utc>>,
+    serializer: S,
+) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    match date {
+        Some(dt) => serializer.serialize_some(&Into::<surrealdb::sql::Datetime>::into(*dt)),
+        None => serializer.serialize_none(),
+    }
+}
+
+pub fn deserialize_option_datetime<'de, D>(
+    deserializer: D,
+) -> Result<Option<DateTime<Utc>>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let value = Option::<surrealdb::sql::Datetime>::deserialize(deserializer)?;
+    Ok(value.map(DateTime::<Utc>::from))
+}