Add parse_program to parser

The `Parser` can now parse a sequence of top-level expressions,
representing a complete program. This change modifies the `roundtrip`
function to iterate over these expressions and emit them, allowing for
multi-line program parsing.

src/ast/parser.rs

@@ -119,6 +119,15 @@ impl<'a> Parser<'a> {
         matches!(self.current_token.kind, TokenKind::EOF)
     }
 
+    /// Parses a complete program as a sequence of top-level expressions.
+    pub fn parse_program(&mut self) -> Vec<SyntaxNode> {
+        let mut expressions = Vec::new();
+        while !self.at_eof() {
+            expressions.push(self.parse_expression());
+        }
+        expressions
+    }
+
     fn synchronize(&mut self) {
         while !self.at_eof() {
             match self.peek() {

src/main.rs

@@ -186,7 +186,7 @@ impl CompilerApp {
 
     fn roundtrip(&mut self) {
         let mut parser = Parser::new(&self.source_code);
-        let ast = parser.parse_expression();
+        let expressions = parser.parse_program();
         if parser.diagnostics.has_errors() {
             let errors: Vec<_> = parser
                 .diagnostics
@@ -198,7 +198,7 @@ impl CompilerApp {
             self.active_tab = AppTab::Output;
             return;
         }
-        self.source_code = emitter::emit(&ast);
+        self.source_code = expressions.iter().map(emitter::emit).collect::<Vec<_>>().join("\n");
         self.output_log = "Roundtrip complete — source reformatted.".to_string();
         self.active_tab = AppTab::Output;
     }

tests/data_server.rs

@@ -120,6 +120,7 @@ fn test_real_m1_full_iteration() {
     assert!(total_records > 0, "Should have read some records");
 }
 
+// FIXME: This test is flaky — thread scheduling can cause uneven read counts.
 #[test]
 fn test_real_concurrent_access() {
     if skip_if_no_data() {