Function make_key 

pub fn make_key(tool_name: &str, args: &Value) -> String

Build a stable cache key from a tool name and JSON arguments.

The result is a 64-character lowercase hex SHA-256 of tool_name + "\0" + canonical_json(args). JSON object keys are sorted recursively before hashing so that two semantically equal argument bags hash to the same key regardless of key insertion order.