Make compaction transitions recoverable

src/runtime.rs

@@ -122,6 +122,7 @@ impl GenerationService {
         turn: TurnSettings,
         messages: Vec<ChatTurn>,
         reason: &str,
+        checkpoint: PathBuf,
         idle_timeout: Duration,
     ) -> Result<ActiveGeneration, String> {
         let cancel = Arc::new(AtomicBool::new(false));
@@ -132,7 +133,7 @@ impl GenerationService {
                 engine,
                 turn,
                 messages,
-                checkpoint: CheckpointTarget::OneShot(PathBuf::new()),
+                checkpoint: CheckpointTarget::Local(checkpoint),
                 compact_reason: Some(reason.to_owned()),
                 idle_timeout,
                 cancel: Arc::clone(&cancel),
@@ -261,10 +262,14 @@ fn run_command(
             });
         };
         if let Some(reason) = &command.compact_reason {
+            let CheckpointTarget::Local(checkpoint) = &command.checkpoint else {
+                unreachable!("compaction checkpoints are local")
+            };
             let result = generator.compact(
                 &command.messages,
                 &command.turn,
                 reason,
+                checkpoint,
                 &command.cancel,
                 &mut progress,
             );