Docs: Add phase_9_79b_3_vm_vtable_thunks_and_pic.md\n- Plan to formalize TypeMeta+Thunk and upgrade PIC to poly\n- Diagnostics, risks, milestones, exit criteria, and Phase 10 readiness

src/runtime/cache_versions.rs

@@ -0,0 +1,30 @@
+//! Global cache version map for vtable/PIC invalidation
+
+use once_cell::sync::Lazy;
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+static CACHE_VERSIONS: Lazy<Mutex<HashMap<String, u32>>> = Lazy::new(|| Mutex::new(HashMap::new()));
+
+/// Get current version for a cache label (default 0)
+pub fn get_version(label: &str) -> u32 {
+    let map = CACHE_VERSIONS.lock().unwrap();
+    *map.get(label).unwrap_or(&0)
+}
+
+/// Bump version for a cache label
+pub fn bump_version(label: &str) {
+    let mut map = CACHE_VERSIONS.lock().unwrap();
+    let e = map.entry(label.to_string()).or_insert(0);
+    *e = e.saturating_add(1);
+}
+
+/// Convenience: bump for multiple labels
+pub fn bump_many(labels: &[String]) {
+    let mut map = CACHE_VERSIONS.lock().unwrap();
+    for l in labels {
+        let e = map.entry(l.clone()).or_insert(0);
+        *e = e.saturating_add(1);
+    }
+}
+