fix(db): add tracing warn for naive timestamp fallback and improve parse_timestamp tests (#1700)

* fix(db): add tracing warn for naive timestamp fallback and improve parse_timestamp tests

* style: fix formatting

src/db/libsql/mod.rs

@@ -17,7 +17,6 @@ mod workspace;
 
 use std::path::Path;
 use std::sync::Arc;
-use std::sync::atomic::{AtomicBool, Ordering};
 
 use async_trait::async_trait;
 use chrono::{DateTime, NaiveDateTime, Utc};
@@ -34,8 +33,6 @@ use crate::workspace::MemoryDocument;
 
 use crate::db::libsql_migrations;
 
-static NAIVE_TIMESTAMP_LOGGED: AtomicBool = AtomicBool::new(false);
-
 /// Explicit column list for routines table (matches positional access in `row_to_routine_libsql`).
 pub(crate) const ROUTINE_COLUMNS: &str = "\
     id, name, description, user_id, enabled, \
@@ -167,13 +164,11 @@ impl LibSqlBackend {
 ///
 /// Returns an error if none of the formats match.
 pub(crate) fn parse_timestamp(s: &str) -> Result<DateTime<Utc>, String> {
-    let log_naive_timestamp_once = || {
-        if !NAIVE_TIMESTAMP_LOGGED.swap(true, Ordering::Relaxed) {
-            tracing::debug!(
-                timestamp = %s,
-                "parsed naive timestamp without timezone; assuming UTC for backward compatibility"
-            );
-        }
+    let log_naive_timestamp = || {
+        tracing::warn!(
+            timestamp = %s,
+            "parsed naive timestamp, assuming UTC — consider migrating to RFC 3339"
+        );
     };
 
     // RFC 3339 (our canonical write format)
@@ -182,12 +177,12 @@ pub(crate) fn parse_timestamp(s: &str) -> Result<DateTime<Utc>, String> {
     }
     // Naive with fractional seconds (legacy or SQLite datetime() output)
     if let Ok(ndt) = NaiveDateTime::parse_from_str(s, "%Y-%m-%d %H:%M:%S%.f") {
-        log_naive_timestamp_once();
+        log_naive_timestamp();
         return Ok(ndt.and_utc());
     }
     // Naive without fractional seconds (legacy format)
     if let Ok(ndt) = NaiveDateTime::parse_from_str(s, "%Y-%m-%d %H:%M:%S") {
-        log_naive_timestamp_once();
+        log_naive_timestamp();
         return Ok(ndt.and_utc());
     }
     Err(format!("unparseable timestamp: {:?}", s))
@@ -439,7 +434,7 @@ mod tests {
     use chrono::{TimeZone, Utc};
 
     use crate::db::Database;
-    use crate::db::libsql::{LibSqlBackend, normalize_notify_user, parse_timestamp};
+    use crate::db::libsql::{LibSqlBackend, fmt_ts, normalize_notify_user, parse_timestamp};
 
     #[test]
     fn test_normalize_notify_user_treats_legacy_default_as_missing() {
@@ -468,6 +463,15 @@ mod tests {
         assert_eq!(naive_without_millis, expected);
     }
 
+    #[test]
+    fn test_fmt_ts_roundtrips_through_parse_timestamp() {
+        let original = Utc.with_ymd_and_hms(2026, 6, 15, 8, 30, 45).unwrap()
+            + chrono::Duration::milliseconds(123);
+        let formatted = fmt_ts(&original);
+        let parsed = parse_timestamp(&formatted).unwrap();
+        assert_eq!(parsed, original);
+    }
+
     #[tokio::test]
     async fn test_libsql_now_format_is_rfc3339_and_parseable() {
         let backend = LibSqlBackend::new_memory().await.unwrap();