Prompt Template Variable Hydrator

Prompt Template Variable Hydrator

When formatting prompts dynamically, you substitute variables into a template. To keep templates clean, they contain placeholders formatted like {variable_name}.

Tasks

Implement the function hydrate_prompt(template, variables, defaults) to:

1. Substitute all placeholders matching {variable_name} with their values from the variables and defaults dictionaries.
2. If a placeholder required by the template is missing from both dictionaries, raise a KeyError with the missing key name.
3. Ensure that if defaults is not provided, it defaults to an empty dictionary.