fix: track add-to-list expression vars in error-handler statement refs

errorHandlerStatementVarRefs in cmd_microflows_builder_flows.go was
still mirroring the old (s.Item, s.List) pattern. For
`add head($SourceItems) to $Items` the expression-valued case, s.Item
is empty and s.Value carries the expression — so $SourceItems was
silently dropped from the reference set used by error-handler flow
analysis (same class of bug ako flagged in validate_microflow.go and
builder_graph.go, which were already fixed).

Walk s.Value when present; fall back to s.Item for the simple-variable
legacy path. New regression test
TestErrorHandlerStatementVarRefsSeesAddExpressionValue guards both the
expression ref and the list ref.

Addresses review feedback on #362.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hjothamendix

mdl/executor/cmd_microflows_builder_add_to_list_test.go

@@ -58,6 +58,37 @@ func TestCollectObjectInputVariablesSeesAddExpressionValue(t *testing.T) {
 	}
 }
 
+func TestErrorHandlerStatementVarRefsSeesAddExpressionValue(t *testing.T) {
+	stmt := &ast.AddToListStmt{
+		Value: &ast.FunctionCallExpr{
+			Name: "head",
+			Arguments: []ast.Expression{
+				&ast.VariableExpr{Name: "SourceItems"},
+			},
+		},
+		List: "Items",
+	}
+
+	refs := errorHandlerStatementVarRefs(stmt)
+
+	seenSource := false
+	seenList := false
+	for _, r := range refs {
+		if r == "SourceItems" {
+			seenSource = true
+		}
+		if r == "Items" {
+			seenList = true
+		}
+	}
+	if !seenSource {
+		t.Errorf("expected $SourceItems to be tracked from add expression: %v", refs)
+	}
+	if !seenList {
+		t.Errorf("expected $Items (list) to be tracked: %v", refs)
+	}
+}
+
 func lastChangeListAction(t *testing.T, fb *flowBuilder) *microflows.ChangeListAction {
 	t.Helper()
 

mdl/executor/cmd_microflows_builder_flows.go

@@ -505,7 +505,12 @@ func errorHandlerStatementVarRefs(stmt ast.MicroflowStatement) []string {
 			refs = append(refs, exprVarRefs(arg)...)
 		}
 	case *ast.AddToListStmt:
-		refs = append(refs, s.Item, s.List)
+		if s.Value != nil {
+			refs = append(refs, exprVarRefs(s.Value)...)
+		} else if s.Item != "" {
+			refs = append(refs, s.Item)
+		}
+		refs = append(refs, s.List)
 	case *ast.RemoveFromListStmt:
 		refs = append(refs, s.Item, s.List)
 	}