RT4a: Synthesize compute nodes for complex return expressions

core/daglang/daglang-cli/tests/workflow_fixtures/s5_ci_pipeline.json

@@ -23,7 +23,7 @@
     "expected_json": {
       "dry_run_completion_required": true,
       "interface_contract_verification_targets": 0,
-      "pure_node_determinism_targets": 220,
+      "pure_node_determinism_targets": 221,
       "resource_acquire_targets": 4,
       "resource_provide_targets": 1,
       "resource_release_targets": 4,
@@ -36,7 +36,7 @@
       "service_transport_permission_scoped_targets": 0,
       "service_transport_prepare_targets": 10,
       "service_transport_readonly_targets": 0,
-      "total_obligations": 230,
+      "total_obligations": 231,
       "transport_execution_targets": 10
     }
   }

core/daglang/daglang-emit/src/computation.rs

@@ -434,6 +434,13 @@ fn classify_primitive(
             outputs,
             body: PureBody::Literal(serde_json::Value::Null),
         }),
+        // RT4a: Return expression compute nodes are resolved at runtime
+        // by the DAG executor, not by the emit pipeline.
+        PrimitiveOpKind::ReturnExprCompute { .. } => Ok(Computation::Pure {
+            inputs,
+            outputs,
+            body: PureBody::Literal(serde_json::Value::Null),
+        }),
     }
 }
 

core/daglang/daglang-emit/src/rust_exec_runtime.rs

@@ -335,6 +335,11 @@ fn classify_handler(op: &LoweredOp) -> Option<HandlerKind> {
             kind: PrimitiveOpKind::ContentUpsertOutputPath { .. },
             ..
         } => return None,
+        // RT4a: Return expression compute nodes are resolved at runtime.
+        LoweredOp::Primitive {
+            kind: PrimitiveOpKind::ReturnExprCompute { .. },
+            ..
+        } => return None,
     }
 
     let (module, name, obligation) = match op {

core/daglang/daglang-lower/src/expr.rs

@@ -205,7 +205,8 @@ fn lower_stmt(stmt: &ast::Stmt, variant_names: &HashSet<String>) -> LoweredStmt
     }
 }
 
-fn lower_expr(expr: &ast::Expr, variant_names: &HashSet<String>) -> LoweredExpr {
+/// Lower a single AST expression to the compiler's expression IR.
+pub fn lower_expr(expr: &ast::Expr, variant_names: &HashSet<String>) -> LoweredExpr {
     match expr {
         ast::Expr::Literal(lit) => LoweredExpr::Literal(lower_literal(lit)),
         // Bare unit variant (e.g., `Closed`)