fix(langchain): convert prompt variables with non-word characters

langfuse/model.py

@@ -163,7 +163,12 @@ def get_langchain_prompt(self) -> Any:
     def _get_langchain_prompt_string(content: str) -> str:
         json_escaped_content = BasePromptClient._escape_json_for_langchain(content)
 
-        return re.sub(r"{{\s*(\w+)\s*}}", r"{\g<1>}", json_escaped_content)
+        # Match any Langfuse variable name between {{ }} (Langfuse allows names
+        # with hyphens, spaces, unicode, etc.), not just \w+. The character class
+        # excludes braces and both quote styles so already-escaped JSON (which
+        # _escape_json_for_langchain doubles to {{"...}} or {{'...}}) is left
+        # untouched.
+        return re.sub(r"{{\s*([^{}\"']+?)\s*}}", r"{\g<1>}", json_escaped_content)
 
     @staticmethod
     def _escape_json_for_langchain(text: str) -> str:

tests/unit/test_prompt_compilation.py

@@ -255,6 +255,48 @@ def test_normal_variables_with_nested_json(self):
 
         assert formatted_prompt == expected
 
+    def test_get_langchain_prompt_preserves_special_variable_names(self):
+        """Variable names with hyphens/spaces/unicode must convert to langchain
+        single-brace placeholders instead of being left as unusable {{...}}."""
+        prompt = TextPromptClient(
+            Prompt_Text(
+                type="text",
+                name="special_var_names",
+                version=1,
+                config={},
+                tags=[],
+                labels=[],
+                prompt="Hello {{user-name}}!",
+            )
+        )
+
+        langchain_prompt_string = prompt.get_langchain_prompt()
+
+        assert langchain_prompt_string == "Hello {user-name}!"
+
+        langchain_prompt = PromptTemplate.from_template(langchain_prompt_string)
+        assert langchain_prompt.input_variables == ["user-name"]
+        assert langchain_prompt.format(**{"user-name": "Ada"}) == "Hello Ada!"
+
+    def test_get_langchain_prompt_leaves_quoted_json_escaped(self):
+        """Brace-pairs wrapping JSON (single- or double-quoted) must stay doubled
+        for langchain, not be converted as if they were variables."""
+        prompt = TextPromptClient(
+            Prompt_Text(
+                type="text",
+                name="json_braces",
+                version=1,
+                config={},
+                tags=[],
+                labels=[],
+                prompt="Reply with {'key': 'value'} and {{name}}",
+            )
+        )
+
+        result = prompt.get_langchain_prompt()
+
+        assert result == "Reply with {{'key': 'value'}} and {name}"
+
     def test_mixed_variables_with_nested_json(self):
         """Test normal variables (double braces) and Langchain variables (single braces) with nested JSON."""
         prompt_string = """Normal variable: {{user_name}}