core: type observability timestamps

apps/admin-api/src/service.rs

@@ -4174,7 +4174,7 @@ impl AdminService {
             error_kind: request.error_kind,
             request_preview: request.request_preview,
             response_preview: request.response_preview,
-            created_at: now_string()?,
+            created_at: OffsetDateTime::now_utc(),
         };
 
         self.registry

apps/mcp-server/src/app.rs

@@ -1821,9 +1821,7 @@ async fn persist_invocation(
     tool: &PublishedAgentTool,
     record: InvocationRecord<'_>,
 ) -> Result<(), crank_registry::RegistryError> {
-    let created_at = OffsetDateTime::now_utc()
-        .format(&Rfc3339)
-        .unwrap_or_else(|_| "1970-01-01T00:00:00Z".to_owned());
+    let created_at = OffsetDateTime::now_utc();
     let duration_ms = u64::try_from(record.duration.as_millis()).unwrap_or(u64::MAX);
     let log = InvocationLog {
         id: InvocationLogId::new(format!("log_{}", uuid::Uuid::now_v7().simple())),