docs/ci: selfhost bootstrap/exe-first workflows; add ny-llvmc scaffolding + JSON v0 schema validation; plan: unify to Nyash ABI v2 (no backwards compat)

src/runtime/gc_trace.rs

@@ -0,0 +1,35 @@
+//! Minimal GC tracing helpers (skeleton)
+//!
+//! Downcast-based child edge enumeration for builtin containers.
+//! This is a non-invasive helper to support diagnostics and future collectors.
+
+use std::sync::Arc;
+
+use crate::box_trait::NyashBox;
+
+/// Visit child boxes of a given object and invoke `visit(child)` for each.
+/// This function recognizes builtin containers (ArrayBox/MapBox) and is a no-op otherwise.
+pub fn trace_children(obj: &dyn NyashBox, visit: &mut dyn FnMut(Arc<dyn NyashBox>)) {
+    // ArrayBox
+    if let Some(arr) = obj.as_any().downcast_ref::<crate::boxes::array::ArrayBox>() {
+        if let Ok(items) = arr.items.read() {
+            for it in items.iter() {
+                // Convert Box<dyn NyashBox> to Arc<dyn NyashBox>
+                let arc: Arc<dyn NyashBox> = Arc::from(it.clone_box());
+                visit(arc);
+            }
+        }
+        return;
+    }
+    // MapBox
+    if let Some(map) = obj.as_any().downcast_ref::<crate::boxes::map_box::MapBox>() {
+        if let Ok(data) = map.get_data().read() {
+            for (_k, v) in data.iter() {
+                let arc: Arc<dyn NyashBox> = Arc::from(v.clone_box());
+                visit(arc);
+            }
+        }
+        return;
+    }
+}
+