Make Reaction polymorphic

Add migration to replace comment_id with polymorphic reactable
association (reactable_type, reactable_id), enabling reactions on both
comments and cards.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

db/migrate/20260121155752_make_reactions_polymorphic.rb

@@ -0,0 +1,27 @@
+class MakeReactionsPolymorphic < ActiveRecord::Migration[8.0]
+  def change
+    add_column :reactions, :reactable_type, :string
+    add_column :reactions, :reactable_id, :uuid
+
+    reversible do |dir|
+      dir.up do
+        execute <<~SQL
+          UPDATE reactions SET reactable_type = 'Comment', reactable_id = comment_id
+        SQL
+      end
+
+      dir.down do
+        execute <<~SQL
+          UPDATE reactions SET comment_id = reactable_id WHERE reactable_type = 'Comment'
+        SQL
+      end
+    end
+
+    change_column_null :reactions, :reactable_type, false
+    change_column_null :reactions, :reactable_id, false
+
+    remove_column :reactions, :comment_id, :uuid
+
+    add_index :reactions, [:reactable_type, :reactable_id]
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2025_12_24_092315) do
+ActiveRecord::Schema[8.2].define(version: 2026_01_21_155752) do
   create_table "accesses", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.datetime "accessed_at"
     t.uuid "account_id", null: false
@@ -412,13 +412,14 @@ ActiveRecord::Schema[8.2].define(version: 2025_12_24_092315) do
 
   create_table "reactions", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.uuid "account_id", null: false
-    t.uuid "comment_id", null: false
     t.string "content", limit: 16, null: false
     t.datetime "created_at", null: false
+    t.uuid "reactable_id", null: false
+    t.string "reactable_type", null: false
     t.uuid "reacter_id", null: false
     t.datetime "updated_at", null: false
     t.index ["account_id"], name: "index_reactions_on_account_id"
-    t.index ["comment_id"], name: "index_reactions_on_comment_id"
+    t.index ["reactable_type", "reactable_id"], name: "index_reactions_on_reactable_type_and_reactable_id"
     t.index ["reacter_id"], name: "index_reactions_on_reacter_id"
   end
 

db/schema_sqlite.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2025_12_24_092315) do
+ActiveRecord::Schema[8.2].define(version: 2026_01_21_155752) do
   create_table "accesses", id: :uuid, force: :cascade do |t|
     t.datetime "accessed_at"
     t.uuid "account_id", null: false
@@ -412,13 +412,14 @@ ActiveRecord::Schema[8.2].define(version: 2025_12_24_092315) do
 
   create_table "reactions", id: :uuid, force: :cascade do |t|
     t.uuid "account_id", null: false
-    t.uuid "comment_id", null: false
     t.string "content", limit: 16, null: false
     t.datetime "created_at", null: false
+    t.uuid "reactable_id", null: false
+    t.string "reactable_type", limit: 255, null: false
     t.uuid "reacter_id", null: false
     t.datetime "updated_at", null: false
     t.index ["account_id"], name: "index_reactions_on_account_id"
-    t.index ["comment_id"], name: "index_reactions_on_comment_id"
+    t.index ["reactable_type", "reactable_id"], name: "index_reactions_on_reactable_type_and_reactable_id"
     t.index ["reacter_id"], name: "index_reactions_on_reacter_id"
   end