diff --git a/web/src/store/attachment.ts b/web/src/store/attachment.ts
index 09ab9a223..d5c2d82a6 100644
--- a/web/src/store/attachment.ts
+++ b/web/src/store/attachment.ts
@@ -4,6 +4,7 @@
  * Manages file attachment state including uploads and metadata.
  * This is a server state store that fetches and caches attachment data.
  */
+import { makeObservable, observable, computed } from "mobx";
 import { attachmentServiceClient } from "@/grpcweb";
 import { CreateAttachmentRequest, Attachment, UpdateAttachmentRequest } from "@/types/proto/api/v1/attachment_service";
 import { StandardState, createServerStore } from "./base-store";
@@ -19,6 +20,15 @@ class AttachmentState extends StandardState {
    */
   attachmentMapByName: Record<string, Attachment> = {};
 
+  constructor() {
+    super();
+    makeObservable(this, {
+      attachmentMapByName: observable,
+      attachments: computed,
+      size: computed,
+    });
+  }
+
   /**
    * Computed getter for all attachments as an array
    */
diff --git a/web/src/store/base-store.ts b/web/src/store/base-store.ts
index 0e27b2abe..d0e9f2bb6 100644
--- a/web/src/store/base-store.ts
+++ b/web/src/store/base-store.ts
@@ -6,7 +6,7 @@
  * - BaseClientStore: For stores that manage UI/client state
  * - Common patterns for all stores
  */
-import { makeAutoObservable } from "mobx";
+import { makeObservable, action } from "mobx";
 import { RequestDeduplicator, StoreError } from "./store-utils";
 
 /**
@@ -166,7 +166,9 @@ export function createClientStore<TState extends BaseState>(state: TState, confi
  */
 export abstract class StandardState implements BaseState {
   constructor() {
-    makeAutoObservable(this);
+    makeObservable(this, {
+      setPartial: action,
+    });
   }
 
   setPartial(partial: Partial<this>): void {