[core] debounce current-time reminders by elapsed time (#29659)

## Summary
- rename `reminder_interval_model_requests` to
`reminder_interval_seconds`
- read the configured time provider before every model request and
inject a reminder only after the configured number of seconds has
elapsed
- preserve immediate first delivery and forced delivery after compaction
changes the context window

## Tests
- `just test -p codex-core current_time_reminder`

codex-rs/core/src/session/time_reminder.rs

@@ -1,3 +1,5 @@
+use chrono::DateTime;
+use chrono::Utc;
 use codex_protocol::error::CodexErr;
 use codex_protocol::error::Result as CodexResult;
 
@@ -7,18 +9,27 @@ use crate::context::ContextualUserFragment;
 
 #[derive(Default)]
 pub(crate) struct CurrentTimeReminderState {
-    model_requests_since_delivery: u64,
+    last_delivery_time: Option<DateTime<Utc>>,
     last_window_id: Option<String>,
 }
 
 impl CurrentTimeReminderState {
-    fn take_reminder_due(&mut self, window_id: &str, interval: u64) -> bool {
-        self.model_requests_since_delivery = self.model_requests_since_delivery.saturating_add(1);
+    fn take_reminder_due(
+        &mut self,
+        window_id: &str,
+        current_time: DateTime<Utc>,
+        interval_seconds: u64,
+    ) -> bool {
         let reminder_is_due = self.last_window_id.as_deref() != Some(window_id)
-            || self.model_requests_since_delivery >= interval;
+            || self.last_delivery_time.is_none_or(|last_delivery_time| {
+                current_time
+                    .signed_duration_since(last_delivery_time)
+                    .num_seconds()
+                    >= i64::try_from(interval_seconds).unwrap_or(i64::MAX)
+            });
 
         if reminder_is_due {
-            self.model_requests_since_delivery = 0;
+            self.last_delivery_time = Some(current_time);
             self.last_window_id = Some(window_id.to_string());
         }
 
@@ -35,16 +46,6 @@ pub(super) async fn maybe_record_current_time_reminder(
         return Ok(());
     };
 
-    let reminder_is_due = {
-        let mut state = sess.state.lock().await;
-        state
-            .current_time_reminder
-            .take_reminder_due(window_id, config.reminder_interval_model_requests)
-    };
-    if !reminder_is_due {
-        return Ok(());
-    }
-
     let current_time = sess
         .services
         .time_provider
@@ -52,6 +53,18 @@ pub(super) async fn maybe_record_current_time_reminder(
         .await
         .map_err(|err| CodexErr::Fatal(format!("failed to read current time: {err:#}")))?;
 
+    let reminder_is_due = {
+        let mut state = sess.state.lock().await;
+        state.current_time_reminder.take_reminder_due(
+            window_id,
+            current_time,
+            config.reminder_interval_seconds,
+        )
+    };
+    if !reminder_is_due {
+        return Ok(());
+    }
+
     let response_item =
         ContextualUserFragment::into(crate::context::CurrentTimeReminder::new(current_time));
     sess.record_conversation_items(turn_context, std::slice::from_ref(&response_item))