fix: hide queue attachment action for messages without attachments

Derive attachment presence from saved queue inputs and only show the preview action when attachments exist. Cover queue metadata and button visibility with regression tests.

Release note: Queued messages without attachments no longer show the View attachments button.

src/main/assistant/assistant-database.ts

@@ -782,7 +782,18 @@ function toSchedule(row: ScheduleWithTaskRow): AssistantSchedule {
 function toConversationQueueItem(
   row: ConversationQueueRow
 ): ConversationQueueItem {
+  let hasAttachments = false
+  if (row.source === 'user' && row.payload_json) {
+    try {
+      const payload = JSON.parse(row.payload_json)
+      const input = payload?.input ?? payload
+      hasAttachments = Array.isArray(input?.attachments) && input.attachments.length > 0
+    } catch {
+      // Invalid queued payloads are reported when previewed or dispatched.
+    }
+  }
   return {
+    hasAttachments,
     id: row.id,
     conversationId: row.conversation_id,
     source: row.source,