fix: suppress CoT output for thinking models

Ref #75

src/heretic/main.py

@@ -200,6 +200,14 @@ def run():
     # a space, which would result in an uncommon tokenization.
     model.response_prefix = commonprefix(responses).rstrip(" ")
 
+    # Suppress CoT output.
+    if model.response_prefix.startswith("<think>"):
+        # Most thinking models.
+        model.response_prefix = "<think></think>"
+    elif model.response_prefix.startswith("<|channel|>analysis<|message|>"):
+        # gpt-oss.
+        model.response_prefix = "<|channel|>analysis<|message|><|end|><|start|>assistant<|channel|>final<|message|>"
+
     if model.response_prefix:
         print(f"* Prefix found: [bold]{model.response_prefix!r}[/]")
     else:

src/heretic/model.py

@@ -288,10 +288,7 @@ class Model:
         )
 
         # Return only the newly generated part.
-        return self.tokenizer.batch_decode(
-            outputs[:, inputs["input_ids"].shape[1] :],
-            skip_special_tokens=True,
-        )
+        return self.tokenizer.batch_decode(outputs[:, inputs["input_ids"].shape[1] :])
 
     def get_responses_batched(self, prompts: list[str]) -> list[str]:
         responses = []