Fix Comment#first_comment_in_thread? UUID string comparison (COPLAN-30)

engine/app/models/coplan/comment.rb

@@ -34,29 +34,25 @@ def author
     private
 
     def first_comment_in_thread?
-      !comment_thread.comments.where("id < ?", id).exists?
+      # IDs are random UUIDs, not insertion-ordered, so we can't compare them
+      # with `id < ?`. after_create_commit guarantees the row is persisted, so
+      # a total count of 1 reliably means this comment opened the thread.
+      comment_thread.comments.count == 1
     end
 
     def notify_plan_author
       CoPlan::NotificationJob.perform_later("comment_created", { comment_thread_id: comment_thread_id })
     end
 
     def track_comment_created
-      # NOTE: We deliberately don't reuse `first_comment_in_thread?` here —
-      # that helper compares UUIDs with `id < ?`, which is not insertion-
-      # ordered. After-create-commit guarantees the row is persisted, so a
-      # total count of 1 is the reliable signal for "this comment opened
-      # the thread."
-      is_first = comment_thread.comments.count == 1
-
       CoPlan::Analytics.track(
         "comment_created",
         user: author,
         plan_id: comment_thread.plan_id,
         comment_thread_id: comment_thread_id,
         comment_id: id,
         author_type: author_type,
-        is_first_in_thread: is_first,
+        is_first_in_thread: first_comment_in_thread?,
         body_length: body_markdown.to_s.length
       )
     end

spec/models/comment_spec.rb

@@ -40,5 +40,20 @@
         create(:comment, comment_thread: thread_record)
       }.not_to have_enqueued_job(CoPlan::NotificationJob)
     end
+
+    # Regression for COPLAN-30: `first_comment_in_thread?` used to compare
+    # UUIDs with `id < ?`, which is not insertion-ordered. A reply whose UUID
+    # sorts before the opener's was wrongly treated as the thread opener,
+    # firing a duplicate "new comment thread" notification for the plan author.
+    it "does not enqueue NotificationJob for a reply whose UUID sorts before the opener" do
+      high_id = "ffffffff-ffff-ffff-ffff-ffffffffffff"
+      low_id  = "00000000-0000-0000-0000-000000000001"
+
+      create(:comment, comment_thread: thread_record, id: high_id)
+
+      expect {
+        create(:comment, comment_thread: thread_record, id: low_id)
+      }.not_to have_enqueued_job(CoPlan::NotificationJob)
+    end
   end
 end