Fix timestamp formats conflict

src/tui/forms.rs

@@ -689,15 +689,12 @@ impl FormController {
                         },
                         _ => return FormAction::Feedback("Manual addressing requires both IPv4 and IPv6 values.".to_owned()),
                     };
-                    let created_utc = match time::OffsetDateTime::now_utc()
-                        .format(&time::format_description::well_known::Rfc3339)
-                    {
-                        Ok(value) => value,
-                        Err(_) => {
-                            return FormAction::Feedback(
-                                "Could not prepare client creation time.".to_owned(),
-                            );
-                        }
+                    let Some(created_utc) =
+                        format_creation_timestamp(time::OffsetDateTime::now_utc())
+                    else {
+                        return FormAction::Feedback(
+                            "Could not prepare client creation time.".to_owned(),
+                        );
                     };
                     let command = UiCommand::CreateClient {
                         alias: alias.trim().to_owned(),
@@ -924,6 +921,13 @@ fn field_value_mut<'a>(
     }
 }
 
+fn format_creation_timestamp(now: time::OffsetDateTime) -> Option<String> {
+    now.replace_nanosecond(0)
+        .ok()?
+        .format(&time::format_description::well_known::Rfc3339)
+        .ok()
+}
+
 trait BoundedString {
     fn push_bounded(&mut self, character: char);
 }
@@ -1054,6 +1058,16 @@ mod tests {
         assert!(matches!(form.handle_key(KeyCode::Esc), FormAction::Cancel));
     }
 
+    #[test]
+    fn creation_timestamp_discards_fractional_seconds_and_renders_as_valid_metadata() {
+        let instant = time::OffsetDateTime::from_unix_timestamp_nanos(1_700_000_000_123_456_789)
+            .expect("fixed UTC instant is in range");
+
+        let timestamp = format_creation_timestamp(instant).expect("timestamp formats");
+        assert_eq!(timestamp, "2023-11-14T22:13:20Z");
+        assert!(crate::wireguard::metadata::render_block("device", Some(&timestamp)).is_ok());
+    }
+
     #[test]
     fn rename_requires_full_key_confirmation_and_restart_exposes_exact_draft_choice() {
         let identity = PublicKey::from_bytes([0x5a; 32]);