diff --git a/kez-chat/web/src/routes/AddClaim.svelte b/kez-chat/web/src/routes/AddClaim.svelte
index ae5470b..18dc69c 100644
--- a/kez-chat/web/src/routes/AddClaim.svelte
+++ b/kez-chat/web/src/routes/AddClaim.svelte
@@ -180,12 +180,20 @@
 
   async function saveAndDone() {
     if (!envelope || !selected) return;
-    await addClaim({
-      id: crypto.randomUUID(),
-      envelope,
-      channel: selected.key,
-    });
-    step = "done";
+    try {
+      // $state wraps `envelope` in a deep Proxy; structuredClone (used
+      // by idb-keyval) can't clone proxies and throws DataCloneError.
+      // $state.snapshot returns a plain, cloneable object.
+      await addClaim({
+        id: crypto.randomUUID(),
+        envelope: $state.snapshot(envelope) as SignedClaimEnvelope,
+        channel: selected.key,
+      });
+      step = "done";
+    } catch (e) {
+      console.error("saveAndDone failed", e);
+      alert(`Failed to save claim: ${(e as Error).message}`);
+    }
   }
 </script>