feat(laguna): add poolside/Laguna-S-2.1 support via a dedicated renderer

renderers/base.py

@@ -1064,10 +1064,13 @@ def bridge_to_next_turn(self, *args: Any, **kwargs: Any) -> "RenderedTokens | No
     # construction to pin a different date.
     "meta-llama/Llama-3.2-1B-Instruct": "llama-3",
     "meta-llama/Llama-3.2-3B-Instruct": "llama-3",
-    # Poolside Laguna. The two checkpoints ship different chat templates,
-    # each mirrored by its own renderer class.
+    # Poolside Laguna. XS.2 and XS-2.1 ship different chat templates, each
+    # mirrored by its own renderer class. S-2.1 is a larger sibling of XS-2.1
+    # with a byte-identical chat template and tokenizer, so it reuses the
+    # XS-2.1 renderer.
     "poolside/Laguna-XS.2": "laguna-xs.2",
     "poolside/Laguna-XS-2.1": "laguna-xs-2.1",
+    "poolside/Laguna-S-2.1": "laguna-xs-2.1",
     # GPT-OSS.
     "openai/gpt-oss-20b": "gpt-oss",
     "openai/gpt-oss-120b": "gpt-oss",

tests/conftest.py

@@ -40,6 +40,9 @@
     # XS-2.1 resolves to `LagunaXS21Renderer` via the model name — its
     # chat template differs from XS.2's (see renderers/laguna_xs2.py).
     ("poolside/Laguna-XS-2.1", "auto"),
+    # S-2.1 is a larger sibling of XS-2.1 with a byte-identical chat template
+    # and tokenizer, so it reuses the XS-2.1 renderer.
+    ("poolside/Laguna-S-2.1", "auto"),
     # DeepSeek-V3/R1 are intentionally NOT in this shared barrage: their
     # chat templates can't render the barrage's tool-call fixtures (the
     # templates require ``tool['type']`` and a string-serialized

tests/test_renderer_config_parity.py

@@ -65,6 +65,7 @@
     ("nvidia/NVIDIA-Nemotron-3-Ultra-550B-A55B-BF16", "auto"),
     ("poolside/Laguna-XS.2", "auto"),
     ("poolside/Laguna-XS-2.1", "auto"),
+    ("poolside/Laguna-S-2.1", "auto"),
     ("tencent/Hy3", "auto"),
     ("openai/gpt-oss-20b", "gpt-oss"),
 ]