feat: optimistic remove — agent vanishes instantly from sidebar

Mirror of the attach optimistic update. onMutate filters the member
out of the cache immediately, rolls back on error, invalidates on
settle to reconcile with server.

desktop/src/features/channels/hooks.ts

@@ -29,12 +29,14 @@ import type {
   AddChannelMembersInput,
   Channel,
   ChannelDetail,
+  ChannelMember,
   CreateChannelInput,
   OpenDmInput,
   SetChannelPurposeInput,
   SetChannelTopicInput,
   UpdateChannelInput,
 } from "@/shared/api/types";
+import { normalizePubkey } from "@/shared/lib/pubkey";
 
 export const channelsQueryKey = ["channels"] as const;
 const channelDetailQueryKey = (channelId: string) =>
@@ -410,6 +412,25 @@ export function useRemoveChannelMemberMutation(channelId: string | null) {
 
       await removeChannelMemberWithManagedAgentCleanup(channelId, pubkey);
     },
+    onMutate: async (pubkey) => {
+      if (!channelId) return;
+      const membersKey = channelMembersQueryKey(channelId);
+      await queryClient.cancelQueries({ queryKey: membersKey });
+      const previous =
+        queryClient.getQueryData<ChannelMember[]>(membersKey) ?? [];
+      queryClient.setQueryData<ChannelMember[]>(
+        membersKey,
+        previous.filter(
+          (m) => normalizePubkey(m.pubkey) !== normalizePubkey(pubkey),
+        ),
+      );
+      return { previous, membersKey };
+    },
+    onError: (_err, _vars, context) => {
+      if (context?.membersKey) {
+        queryClient.setQueryData(context.membersKey, context.previous);
+      }
+    },
     onSettled: async () => {
       await Promise.all([
         invalidateChannelState(queryClient, channelId),