feat(unseal): add unseal protocol and crypto infrastructure

server/crates/arbiter-server/src/context/lease.rs

@@ -0,0 +1,41 @@
+use std::sync::Arc;
+
+use dashmap::DashSet;
+
+#[derive(Clone, Default)]
+struct LeaseStorage<T: Eq + std::hash::Hash>(Arc<DashSet<T>>);
+
+// A lease that automatically releases the item when dropped
+pub struct Lease<T: Clone + std::hash::Hash + Eq> {
+    item: T,
+    storage: LeaseStorage<T>,
+}
+impl<T: Clone + std::hash::Hash + Eq> Drop for Lease<T> {
+    fn drop(&mut self) {
+        self.storage.0.remove(&self.item);
+    }
+}
+
+#[derive(Clone, Default)]
+pub struct LeaseHandler<T: Clone + std::hash::Hash + Eq> {
+    storage: LeaseStorage<T>,
+}
+
+impl<T: Clone + std::hash::Hash + Eq> LeaseHandler<T> {
+    pub fn new() -> Self {
+        Self {
+            storage: LeaseStorage(Arc::new(DashSet::new())),
+        }
+    }
+
+    pub fn acquire(&self, item: T) -> Result<Lease<T>, ()> {
+        if self.storage.0.insert(item.clone()) {
+            Ok(Lease {
+                item,
+                storage: self.storage.clone(),
+            })
+        } else {
+            Err(())
+        }
+    }
+}