feat: add find_last_slot_per_block method to schedule repositories and update related logic

k-tv-backend/domain/src/repositories.rs

@@ -3,6 +3,8 @@
 //! These traits define the interface for data persistence.
 //! Implementations live in the infra layer.
 
+use std::collections::HashMap;
+
 use async_trait::async_trait;
 use chrono::DateTime;
 use chrono::Utc;
@@ -10,7 +12,7 @@ use uuid::Uuid;
 
 use crate::entities::{Channel, GeneratedSchedule, PlaybackRecord, User};
 use crate::errors::DomainResult;
-use crate::value_objects::{ChannelId, UserId};
+use crate::value_objects::{BlockId, ChannelId, MediaItemId, UserId};
 
 /// An in-app activity event stored in the database for the admin log view.
 #[derive(Debug, Clone)]
@@ -98,6 +100,13 @@ pub trait ScheduleRepository: Send + Sync {
     ) -> DomainResult<Vec<PlaybackRecord>>;
 
     async fn save_playback_record(&self, record: &PlaybackRecord) -> DomainResult<()>;
+
+    /// Return the most recent slot per block_id across ALL schedules for a channel.
+    /// Resilient to any single generation having empty slots for a block.
+    async fn find_last_slot_per_block(
+        &self,
+        channel_id: ChannelId,
+    ) -> DomainResult<HashMap<BlockId, MediaItemId>>;
 }
 
 /// Repository port for activity log persistence.