fix(generation): handle missing chat template and add HRM-Text-1B fallback

app/generation/prompting.py

@@ -18,11 +18,22 @@ def build_messages(question: str) -> list[dict[str, str]]:
 
 def render_prompt(tokenizer: Any, question: str) -> str:
     messages = build_messages(question)
-    if hasattr(tokenizer, "apply_chat_template"):
-        return tokenizer.apply_chat_template(
-            messages,
-            tokenize=False,
-            add_generation_prompt=True,
-        )
-
-    return f"{SYSTEM_PROMPT}\n\nQuestion: {question}\n"
+    if hasattr(tokenizer, "apply_chat_template") and getattr(tokenizer, "chat_template", None) is not None:
+        try:
+            return tokenizer.apply_chat_template(
+                messages,
+                tokenize=False,
+                add_generation_prompt=True,
+            )
+        except Exception:
+            pass
+
+    # Fallback for models without a chat template
+    # Special handling for HRM-Text-1B which requires specific condition tokens
+    model_name = getattr(tokenizer, "name_or_path", "")
+    if model_name and "HRM-Text-1B" in model_name:
+        # Use the synth,cot prefix as recommended for this model
+        prefix = "<|im_start|><|quad_end|><|object_ref_end|><|im_end|>"
+        return f"{prefix}{SYSTEM_PROMPT}\n\nUser: {question}\n\nAssistant:"
+
+    return f"{SYSTEM_PROMPT}\n\nUser: {question}\n\nAssistant:"