fix(engine): use depth-based cursor restoration in Call/Return

crates/plotnik-lib/src/engine/cursor.rs

@@ -78,6 +78,18 @@ impl<'t> CursorWrapper<'t> {
         self.cursor.field_id()
     }
 
+    /// Get current tree depth (root is 0).
+    #[inline]
+    pub fn depth(&self) -> u32 {
+        self.cursor.depth()
+    }
+
+    /// Move cursor to parent node.
+    #[inline]
+    pub fn goto_parent(&mut self) -> bool {
+        self.cursor.goto_parent()
+    }
+
     /// Check if a node type is trivia.
     #[inline]
     pub fn is_trivia(&self, node: &Node<'_>) -> bool {

crates/plotnik-lib/src/engine/frame.rs

@@ -10,8 +10,8 @@ pub struct Frame {
     pub return_addr: u16,
     /// Parent frame index (for cactus stack).
     pub parent: Option<u32>,
-    /// Cursor position before Call navigation (for restoration on Return).
-    pub cursor_position: u32,
+    /// Tree depth at Call time (for level restoration on Return).
+    pub saved_depth: u32,
 }
 
 /// Append-only arena for frames (cactus stack implementation).
@@ -35,25 +35,25 @@ impl FrameArena {
     }
 
     /// Push a new frame, returns its index.
-    pub fn push(&mut self, return_addr: u16, cursor_position: u32) -> u32 {
+    pub fn push(&mut self, return_addr: u16, saved_depth: u32) -> u32 {
         let idx = self.frames.len() as u32;
         self.frames.push(Frame {
             return_addr,
             parent: self.current,
-            cursor_position,
+            saved_depth,
         });
         self.current = Some(idx);
         idx
     }
 
-    /// Pop the current frame, returning its return address and cursor position.
+    /// Pop the current frame, returning its return address and saved depth.
     ///
     /// Panics if the stack is empty.
     pub fn pop(&mut self) -> (u16, u32) {
         let current_idx = self.current.expect("pop on empty frame stack");
         let frame = self.frames[current_idx as usize];
         self.current = frame.parent;
-        (frame.return_addr, frame.cursor_position)
+        (frame.return_addr, frame.saved_depth)
     }
 
     /// Restore frame state for backtracking.

crates/plotnik-lib/src/engine/vm.rs

@@ -231,12 +231,13 @@ impl<'t> VM<'t> {
 
         self.navigate_to_field(c.nav, c.node_field, tracer)?;
 
-        // Save cursor position AFTER navigation - this is where the callee starts matching.
-        // On Return, we restore to this position so Nav::Next in quantifier loops works correctly.
-        let saved_cursor = self.cursor.descendant_index();
+        // Save tree depth AFTER navigation. On Return, we go up to this depth.
+        // This allows continue_search advances at the same level to be preserved,
+        // while still restoring level when the callee descended into children.
+        let saved_depth = self.cursor.depth();
 
         tracer.trace_call(c.target.get());
-        self.frames.push(c.next.get(), saved_cursor);
+        self.frames.push(c.next.get(), saved_depth);
         self.recursion_depth += 1;
         self.ip = c.target.get();
         Ok(())
@@ -296,18 +297,24 @@ impl<'t> VM<'t> {
             return Err(RuntimeError::Accept);
         }
 
-        let (return_addr, saved_cursor) = self.frames.pop();
+        let (return_addr, saved_depth) = self.frames.pop();
         self.recursion_depth -= 1;
 
         // Prune frames (O(1) amortized)
         self.frames.prune(self.checkpoints.max_frame_ref());
 
-        // Set matched_node BEFORE restoring cursor so effects after
+        // Set matched_node BEFORE going up so effects after
         // a Call can capture the node that the callee matched.
         self.matched_node = Some(self.cursor.node());
 
-        // Restore cursor position for subsequent navigation (e.g., Nav::Next in quantifier loop)
-        self.cursor.goto_descendant(saved_cursor);
+        // Go up to saved depth level. This preserves sibling advances
+        // (continue_search at same level) while restoring level when
+        // the callee descended into children.
+        while self.cursor.depth() > saved_depth {
+            if !self.cursor.goto_parent() {
+                break;
+            }
+        }
 
         self.ip = return_addr;
         Ok(())