fix: Reset model after saving merged model (#321)

* fix: Reset model after saving merged model

The adapter is lost and writes 0-byte adapters if you save an adapter after saving the merged model.

* Revert "Revert "Revert "fix: disable LoRA export for now" (#308)" (#319)"

This reverts commit 216c089974.

* Add comment as to why resetting model is needed

src/heretic/main.py

@@ -145,18 +145,13 @@ def obtain_merge_strategy(settings: Settings, model: Model) -> str | None:
                 value="merge",
             ),
             Choice(
-                    title="Cancel",
+                title="Save LoRA adapter only (can be merged later)",
-                    value="cancel",
+                value="adapter",
             ),
         ],
     )
 
-        if strategy == "cancel":
-            return None
-
     return strategy
-    else:
-        return "merge"
 
 
 def run():
@@ -754,6 +749,10 @@ def run():
             print("* Parameters:")
             for name, value in get_trial_parameters(trial).items():
                 print(f"  * {name} = [bold]{value}[/]")
+
+            # Per https://github.com/huggingface/peft/issues/868#issuecomment-1820642893 once a LoRA is merged it's
+            # expected to be empty. Provide a utility function to restore the previous LoRA-ified state.
+            def reset_trial_model() -> None:
                 print("* Resetting model...")
                 model.reset_model()
                 print("* Abliterating...")
@@ -766,6 +765,8 @@ def run():
                     },
                 )
 
+            reset_trial_model()
+
             while True:
                 print()
                 action = prompt_select(
@@ -812,6 +813,7 @@ def run():
                                 del merged_model
                                 empty_cache()
                                 model.tokenizer.save_pretrained(save_directory)
+                                reset_trial_model()
 
                             print(f"Model saved to [bold]{save_directory}[/].")
 
@@ -921,6 +923,7 @@ def run():
                                     private=private,
                                     token=token,
                                 )
+                                reset_trial_model()
 
                             if is_hf_path(settings.model):
                                 card = ModelCard.load(settings.model)