fix(channels): fix optimistically insert attachments

[synoet]

• attachments where previously not being optimistically inserted

[github-actions]

Preview: https://synoet-optimistic-attachments-g250vz.preview.macro.com/app (78917cb)

[claude]

Code review

Bug found: Optimistic attachments lose their association after message ID replacement

In js/app/packages/queries/channel/message.ts:77-83, the optimistic attachments are created with message_id: vars.optimisticId:

const newAttachments: Attachment[] = vars.attachments.map((a) => ({
  id: crypto.randomUUID(),
  channel_id: vars.channelId,
  created_at: String(Date.now()),
  message_id: vars.optimisticId,  // <-- Uses optimistic ID
  ...a,
}));

When the mutation succeeds, replaceOptimisticMessage is called, which updates the message's id from optimisticId to realId. However, the replaceOptimisticMessage function only updates messages and does NOT update the attachments' message_id field.

In MessageContainer.tsx:299, attachments are filtered by a.message_id === message.id, which will fail after ID replacement because:

• message.id = realId (new server-assigned ID)
• attachment.message_id = optimisticId (old ID that was never updated)

Result: Attachments will briefly show when the message is first sent, then disappear after the server responds, until the next cache refetch.

Fix: Update replaceOptimisticMessage to also replace the message_id for attachments:

return {
  ...prev,
  messages: updatedMessages,
  attachments: prev.attachments.map((a) =>
    a.message_id === vars.optimisticId
      ? { ...a, message_id: vars.realId }
      : a
  ),
};