feat(dataflow): model production SQL flow patterns

src/govoplan_dataflow/backend/ir.py

@@ -279,26 +279,43 @@ def _node_expressions(
     node: GraphNode,
     output_state: SchemaState,
 ) -> tuple[IrExpression, ...]:
+    if node.type == "calculate":
+        sources = [
+            str(item.get("expression") or "")
+            for item in node.config.get("calculations", [])
+            if isinstance(item, dict) and item.get("expression")
+        ]
+        return tuple(
+            item
+            for source in sources
+            if (item := _ir_expression(source, output_state)) is not None
+        )
     source = node.config.get("expression")
     if node.type not in {"expression", "filter.expression"} or not source:
         return ()
+    expression = _ir_expression(str(source), output_state)
+    return (expression,) if expression is not None else ()
+
+
+def _ir_expression(
+    source: str,
+    output_state: SchemaState,
+) -> IrExpression | None:
     try:
         parsed = parse_expression(str(source))
     except ExpressionError:
-        return ()
+        return None
     inferred = infer_expression_type(parsed, output_state.types)
-    return (
-        IrExpression(
-            source=parsed.source,
-            columns=parsed.columns,
-            result_type=_data_type(inferred),
-            semantic_hash=_hash_payload(
-                {
-                    "dialect": "duckdb",
-                    "source": parsed.sql(),
-                    "result_type": inferred,
-                }
-            ),
+    return IrExpression(
+        source=parsed.source,
+        columns=parsed.columns,
+        result_type=_data_type(inferred),
+        semantic_hash=_hash_payload(
+            {
+                "dialect": "duckdb",
+                "source": parsed.sql(),
+                "result_type": inferred,
+            }
         ),
     )