feat(control_tree): add StepTreeContract and signature (dev-only)

src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs

@@ -70,6 +70,18 @@ pub(crate) fn detect_break_in_body(body: &[ASTNode]) -> bool {
     false
 }
 
+/// Detect if a loop body contains return statements
+///
+/// This is used for dev-only parity checks with structure SSOT (StepTree).
+pub(crate) fn detect_return_in_body(body: &[ASTNode]) -> bool {
+    for stmt in body {
+        if has_return_node(stmt) {
+            return true;
+        }
+    }
+    false
+}
+
 /// Extract full feature set from loop body AST
 ///
 /// This is the main entry point for feature extraction. It analyzes the loop body
@@ -273,6 +285,26 @@ fn has_break_node(node: &ASTNode) -> bool {
     }
 }
 
+/// Recursive helper to check if AST node contains return
+fn has_return_node(node: &ASTNode) -> bool {
+    match node {
+        ASTNode::Return { .. } => true,
+        ASTNode::If {
+            then_body,
+            else_body,
+            ..
+        } => {
+            then_body.iter().any(has_return_node)
+                || else_body
+                    .as_ref()
+                    .map_or(false, |e| e.iter().any(has_return_node))
+        }
+        ASTNode::Loop { body, .. } => body.iter().any(has_return_node),
+        ASTNode::ScopeBox { body, .. } => body.iter().any(has_return_node),
+        _ => false,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;