diff --git a/studio/frontend/src/features/chat/runtime-provider.tsx b/studio/frontend/src/features/chat/runtime-provider.tsx
index bdf4e528d8..716fa1d633 100644
--- a/studio/frontend/src/features/chat/runtime-provider.tsx
+++ b/studio/frontend/src/features/chat/runtime-provider.tsx
@@ -1017,6 +1017,15 @@ function ActiveThreadSync({
     if (!enabled) {
       return;
     }
+    // Don't clobber a persisted activeThreadId while aui is still booting
+    // up. mainThreadId starts null on every page load before aui's async
+    // thread init finishes; without this guard we'd reset our persisted
+    // draft id to null and lose the doc chip mapping for that thread.
+    // Explicit clears (new chat / thread delete) go through
+    // setActiveThreadId(null) directly and bypass this effect.
+    if (!mainThreadId) {
+      return;
+    }
     const persisted = useChatRuntimeStore.getState().activeThreadId;
     // On page reload aui mints a fresh `__LOCALID_*` for its draft thread.
     // If we already have a persisted draft id, keep it so any RAG docs
@@ -1024,15 +1033,14 @@ function ActiveThreadSync({
     // chat history for the new mainThreadId starts empty either way, so
     // this only affects what we treat as the active id for doc/RAG lookup.
     if (
-      mainThreadId
-      && persisted
+      persisted
       && persisted !== mainThreadId
       && persisted.startsWith("__LOCALID_")
       && mainThreadId.startsWith("__LOCALID_")
     ) {
       return;
     }
-    setActiveThreadId(mainThreadId ?? null);
+    setActiveThreadId(mainThreadId);
   }, [enabled, mainThreadId, setActiveThreadId]);
 
   return null;