feat: Full support for map node types

src/graph/reducer.rs

@@ -1,6 +1,7 @@
 use super::types::Reducer;
 use anyhow::{Result, bail};
 use serde_json::{Number, Value};
+use crate::graph::type_name;
 
 /// Combines a branch's incoming write with the current state value (if any)
 /// via the specified reducer. The result is what gets written back to live
@@ -147,17 +148,6 @@ fn number_or_error(value: &Value, reducer_name: &str, position: &str) -> Result<
     }
 }
 
-fn type_name(value: &Value) -> &'static str {
-    match value {
-        Value::Null => "null",
-        Value::Bool(_) => "bool",
-        Value::Number(_) => "number",
-        Value::String(_) => "string",
-        Value::Array(_) => "array",
-        Value::Object(_) => "object",
-    }
-}
-
 // Numeric reducers compute in f64 for simplicity. We preserve integer typing
 // when the result is losslessly representable as i64 so `count: sum` stays an
 // integer rather than degrading to a float. Non-finite values (NaN, Inf) can't