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())),

crates/crank-core/src/observability.rs

@@ -1,5 +1,6 @@
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
+use time::OffsetDateTime;
 
 use crate::{AgentId, OperationId, WorkspaceId};
 
@@ -63,7 +64,8 @@ pub struct InvocationLog {
     pub error_kind: Option<String>,
     pub request_preview: Value,
     pub response_preview: Value,
-    pub created_at: String,
+    #[serde(with = "time::serde::rfc3339")]
+    pub created_at: OffsetDateTime,
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
@@ -79,3 +81,52 @@ pub struct UsageRollup {
     pub p95_ms: u64,
     pub p99_ms: u64,
 }
+
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+    use time::{OffsetDateTime, format_description::well_known::Rfc3339};
+
+    use super::{InvocationLevel, InvocationLog, InvocationSource, InvocationStatus, UsagePeriod};
+    use crate::{AgentId, OperationId, WorkspaceId, ids::InvocationLogId};
+
+    fn timestamp(value: &str) -> OffsetDateTime {
+        OffsetDateTime::parse(value, &Rfc3339).unwrap()
+    }
+
+    #[test]
+    fn invocation_log_serializes_timestamps_as_rfc3339() {
+        let log = InvocationLog {
+            id: InvocationLogId::new("log_01"),
+            workspace_id: WorkspaceId::new("ws_01"),
+            agent_id: Some(AgentId::new("agent_01")),
+            operation_id: OperationId::new("op_01"),
+            source: InvocationSource::AdminTestRun,
+            level: InvocationLevel::Info,
+            status: InvocationStatus::Ok,
+            tool_name: "create_lead".to_owned(),
+            message: "ok".to_owned(),
+            request_id: Some("req_01".to_owned()),
+            status_code: Some(200),
+            duration_ms: 123,
+            error_kind: None,
+            request_preview: json!({"input": "value"}),
+            response_preview: json!({"ok": true}),
+            created_at: timestamp("2026-04-19T12:34:56Z"),
+        };
+
+        let value = serde_json::to_value(&log).unwrap();
+
+        assert_eq!(value["created_at"], "2026-04-19T12:34:56Z");
+        assert_eq!(value["source"], "admin_test_run");
+        assert_eq!(value["level"], "info");
+        assert_eq!(value["status"], "ok");
+    }
+
+    #[test]
+    fn usage_period_serializes_compact_labels() {
+        let value = serde_json::to_value(UsagePeriod::Last7Days).unwrap();
+
+        assert_eq!(value, "7d");
+    }
+}

crates/crank-registry/src/model.rs

@@ -130,7 +130,8 @@ pub struct UsageRollupRecord {
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub struct UsageTimelinePoint {
-    pub bucket_start: String,
+    #[serde(with = "time::serde::rfc3339")]
+    pub bucket_start: OffsetDateTime,
     pub calls_ok: u64,
     pub calls_error: u64,
 }

crates/crank-registry/src/postgres/mod.rs

@@ -2496,7 +2496,7 @@ mod tests {
             error_kind: None,
             request_preview: json!({"input":"value"}),
             response_preview: json!({"ok":true}),
-            created_at: created_at.to_owned(),
+            created_at: timestamp(created_at),
         }
     }
 

crates/crank-registry/src/postgres/observability.rs

@@ -47,7 +47,7 @@ impl PostgresRegistry {
         .bind(&request.log.error_kind)
         .bind(Json(request.log.request_preview.clone()))
         .bind(Json(request.log.response_preview.clone()))
-        .bind(&request.log.created_at)
+        .bind(request.log.created_at)
         .execute(&self.pool)
         .await?;
 
@@ -75,7 +75,7 @@ impl PostgresRegistry {
                 l.error_kind,
                 l.request_preview_json,
                 l.response_preview_json,
-                to_char(l.created_at at time zone 'UTC', 'YYYY-MM-DD\"T\"HH24:MI:SS.MS\"Z\"') as created_at,
+                l.created_at as created_at,
                 o.name as operation_name,
                 o.display_name as operation_display_name,
                 a.slug as agent_slug,
@@ -147,7 +147,7 @@ impl PostgresRegistry {
                 l.error_kind,
                 l.request_preview_json,
                 l.response_preview_json,
-                to_char(l.created_at at time zone 'UTC', 'YYYY-MM-DD\"T\"HH24:MI:SS.MS\"Z\"') as created_at,
+                l.created_at as created_at,
                 o.name as operation_name,
                 o.display_name as operation_display_name,
                 a.slug as agent_slug,
@@ -229,7 +229,7 @@ impl PostgresRegistry {
         let bucket = usage_bucket_sql(query.bucket);
         let sql = format!(
             "select
-                to_char(date_trunc('{bucket}', created_at at time zone 'UTC'), 'YYYY-MM-DD\"T\"HH24:MI:SS\"Z\"') as bucket_start,
+                (date_trunc('{bucket}', created_at at time zone 'UTC') at time zone 'UTC') as bucket_start,
                 count(*) filter (where status = 'ok')::bigint as calls_ok,
                 count(*) filter (where status = 'error')::bigint as calls_error
              from invocation_logs