fix: patch bug in system prompt formatter that was triggering if you … (#785)

letta/services/helpers/agent_manager_helper.py

@@ -118,6 +118,27 @@ def compile_memory_metadata_block(
     return memory_metadata_block
 
 
+class PreserveMapping(dict):
+    """Used to preserve (do not modify) undefined variables in the system prompt"""
+
+    def __missing__(self, key):
+        return "{" + key + "}"
+
+
+def safe_format(template: str, variables: dict) -> str:
+    """
+    Safely formats a template string, preserving empty {} and {unknown_vars}
+    while substituting known variables.
+
+    If we simply use {} in format_map, it'll be treated as a positional field
+    """
+    # First escape any empty {} by doubling them
+    escaped = template.replace("{}", "{{}}")
+
+    # Now use format_map with our custom mapping
+    return escaped.format_map(PreserveMapping(variables))
+
+
 def compile_system_message(
     system_prompt: str,
     in_context_memory: Memory,
@@ -169,7 +190,8 @@ def compile_system_message(
 
         # render the variables using the built-in templater
         try:
-            formatted_prompt = system_prompt.format_map(variables)
+            formatted_prompt = safe_format(system_prompt, variables)
+            print(f"Formatted system prompt:\n{formatted_prompt}")
         except Exception as e:
             raise ValueError(f"Failed to format system prompt - {str(e)}. System prompt value:\n{system_prompt}")
 

tests/test_system_prompt_compiler.py

@@ -0,0 +1,59 @@
+from letta.services.helpers.agent_manager_helper import safe_format
+
+CORE_MEMORY_VAR = "My core memory is that I like to eat bananas"
+VARS_DICT = {"CORE_MEMORY": CORE_MEMORY_VAR}
+
+
+def test_formatter():
+
+    # Example system prompt that has no vars
+    NO_VARS = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    """
+
+    assert NO_VARS == safe_format(NO_VARS, VARS_DICT)
+
+    # Example system prompt that has {CORE_MEMORY}
+    CORE_MEMORY_VAR = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    {CORE_MEMORY}
+    """
+
+    CORE_MEMORY_VAR_SOL = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    My core memory is that I like to eat bananas
+    """
+
+    assert CORE_MEMORY_VAR_SOL == safe_format(CORE_MEMORY_VAR, VARS_DICT)
+
+    # Example system prompt that has {CORE_MEMORY} and {USER_MEMORY} (latter doesn't exist)
+    UNUSED_VAR = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    {USER_MEMORY}
+    {CORE_MEMORY}
+    """
+
+    UNUSED_VAR_SOL = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    {USER_MEMORY}
+    My core memory is that I like to eat bananas
+    """
+
+    assert UNUSED_VAR_SOL == safe_format(UNUSED_VAR, VARS_DICT)
+
+    # Example system prompt that has {CORE_MEMORY} and {USER_MEMORY} (latter doesn't exist), AND an empty {}
+    UNUSED_AND_EMPRY_VAR = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    {}
+    {USER_MEMORY}
+    {CORE_MEMORY}
+    """
+
+    UNUSED_AND_EMPRY_VAR_SOL = """
+    THIS IS A SYSTEM PROMPT WITH NO VARS
+    {}
+    {USER_MEMORY}
+    My core memory is that I like to eat bananas
+    """
+
+    assert UNUSED_AND_EMPRY_VAR_SOL == safe_format(UNUSED_AND_EMPRY_VAR, VARS_DICT)