diff --git a/Gemfile.lock b/Gemfile.lock
index 43d4e718b..2f87d5cff 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,7 +6,7 @@ GIT
 
 GIT
   remote: https://github.com/rails/rails.git
-  revision: 3c3f6c8a253c8a0f346695374f927c9ab32fbefb
+  revision: 3d105fc346fbb3121bbcf6340f2b19104bf326f0
   branch: main
   specs:
     actioncable (8.2.0.alpha)
diff --git a/Gemfile.saas.lock b/Gemfile.saas.lock
index 0c8880b08..18f80a22f 100644
--- a/Gemfile.saas.lock
+++ b/Gemfile.saas.lock
@@ -75,7 +75,7 @@ GIT
 
 GIT
   remote: https://github.com/rails/rails.git
-  revision: 690ec8898318b8f50714e86676353ebe1551261e
+  revision: 3d105fc346fbb3121bbcf6340f2b19104bf326f0
   branch: main
   specs:
     actioncable (8.2.0.alpha)
@@ -292,7 +292,7 @@ GEM
       actionview (>= 7.0.0)
       activesupport (>= 7.0.0)
     jmespath (1.6.2)
-    json (2.16.0)
+    json (2.17.1)
     jwt (3.1.2)
       base64
     kamal (2.9.0)
@@ -552,7 +552,7 @@ GEM
       ostruct
     stimulus-rails (1.3.4)
       railties (>= 6.0.0)
-    stringio (3.1.8)
+    stringio (3.1.9)
     thor (1.4.0)
     thruster (0.1.16)
     thruster (0.1.16-aarch64-linux)
diff --git a/app/models/concerns/attachments.rb b/app/models/concerns/attachments.rb
index 1d1c2c4d6..bcc7303ae 100644
--- a/app/models/concerns/attachments.rb
+++ b/app/models/concerns/attachments.rb
@@ -1,13 +1,10 @@
 module Attachments
   extend ActiveSupport::Concern
 
-  # The variants we use must all declared here so that we can preprocess them.
+  # Variants used by ActionText embeds. Processed immediately on attachment to avoid
+  # read replica issues (lazy variants would attempt writes on read replicas).
   #
-  # If they are not preprocessed, then Rails will attempt to transform the image on-the-fly when
-  # they are first viewed, which may be on the read replica where writing to the database is not
-  # allowed. Chaos will ensue if that happens.
-  #
-  # These variants are patched into ActionText::RichText in config/initializers/action_text.rb
+  # Patched into ActionText::RichText in config/initializers/action_text.rb
   VARIANTS = {
     # vipsthumbnail used to create sized image variants has a intent setting to manage colors during
     # resize. By setting an invalid intent value the gif-incompatible intent filtering is skipped and
diff --git a/app/models/user/avatar.rb b/app/models/user/avatar.rb
index a4b2ae631..c635edddb 100644
--- a/app/models/user/avatar.rb
+++ b/app/models/user/avatar.rb
@@ -5,7 +5,7 @@ module User::Avatar
 
   included do
     has_one_attached :avatar do |attachable|
-      attachable.variant :thumb, resize_to_fill: [ 256, 256 ]
+      attachable.variant :thumb, resize_to_fill: [ 256, 256 ], process: :immediately
     end
 
     validate :avatar_content_type_allowed
diff --git a/config/initializers/action_text.rb b/config/initializers/action_text.rb
index b2724b1c7..eee87de0d 100644
--- a/config/initializers/action_text.rb
+++ b/config/initializers/action_text.rb
@@ -7,7 +7,7 @@ module ActionText
         # This overrides the default :embeds association!
         has_many_attached :embeds do |attachable|
           ::Attachments::VARIANTS.each do |variant_name, variant_options|
-            attachable.variant variant_name, variant_options.merge(preprocessed: true)
+            attachable.variant variant_name, **variant_options, process: :immediately
           end
         end
       end
diff --git a/test/controllers/users/avatars_controller_test.rb b/test/controllers/users/avatars_controller_test.rb
index 3ded884b8..be4532448 100644
--- a/test/controllers/users/avatars_controller_test.rb
+++ b/test/controllers/users/avatars_controller_test.rb
@@ -27,7 +27,9 @@ class Users::AvatarsControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "show own image redirects to the blob url" do
-    users(:david).avatar.attach(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    # Create blob separately to ensure file is uploaded before variant processing
+    blob = ActiveStorage::Blob.create_and_upload!(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    users(:david).avatar.attach(blob)
     assert users(:david).avatar.attached?
 
     get user_avatar_path(users(:david))
@@ -36,7 +38,9 @@ class Users::AvatarsControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "show other image redirects to the blob url" do
-    users(:kevin).avatar.attach(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    # Create blob separately to ensure file is uploaded before variant processing
+    blob = ActiveStorage::Blob.create_and_upload!(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    users(:kevin).avatar.attach(blob)
     assert users(:kevin).avatar.attached?
 
     get user_avatar_path(users(:kevin))
diff --git a/test/mailers/notification/bundle_mailer_test.rb b/test/mailers/notification/bundle_mailer_test.rb
index fbc4274c9..63647e68a 100644
--- a/test/mailers/notification/bundle_mailer_test.rb
+++ b/test/mailers/notification/bundle_mailer_test.rb
@@ -22,11 +22,12 @@ class Notification::BundleMailerTest < ActionMailer::TestCase
   end
 
   test "renders avatar with external image URL when avatar is attached" do
-    @user.avatar.attach(
+    blob = ActiveStorage::Blob.create_and_upload!(
       io: File.open(Rails.root.join("test", "fixtures", "files", "avatar.png")),
       filename: "avatar.png",
       content_type: "image/png"
     )
+    @user.avatar.attach(blob)
 
     create_notification(@user)
 
diff --git a/test/models/comment_test.rb b/test/models/comment_test.rb
index c519f8fbd..13a5e36c3 100644
--- a/test/models/comment_test.rb
+++ b/test/models/comment_test.rb
@@ -4,4 +4,24 @@ class CommentTest < ActiveSupport::TestCase
   setup do
     Current.session = sessions(:david)
   end
+
+  test "rich text embed variants are processed immediately on attachment" do
+    comment = cards(:logo).comments.create!(body: "Check this out")
+    comment.body.body.attachables # force load
+
+    blob = ActiveStorage::Blob.create_and_upload! \
+      io: File.open(file_fixture("moon.jpg")),
+      filename: "moon.jpg",
+      content_type: "image/jpeg"
+
+    comment.body.body = ActionText::Content.new(comment.body.body.to_html).append_attachables(blob)
+    comment.save!
+
+    embed = comment.body.embeds.sole
+
+    Attachments::VARIANTS.each_key do |variant_name|
+      variant = embed.variant(variant_name)
+      assert variant.processed?, "Expected #{variant_name} variant to be processed immediately"
+    end
+  end
 end
diff --git a/test/models/user/avatar_test.rb b/test/models/user/avatar_test.rb
index 96ea5bac7..58b78969c 100644
--- a/test/models/user/avatar_test.rb
+++ b/test/models/user/avatar_test.rb
@@ -2,7 +2,8 @@ require "test_helper"
 
 class User::AvatarTest < ActiveSupport::TestCase
   test "avatar_thumbnail returns variant for variable images" do
-    users(:david).avatar.attach(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    blob = ActiveStorage::Blob.create_and_upload!(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+    users(:david).avatar.attach(blob)
 
     assert users(:david).avatar.variable?
     assert_equal users(:david).avatar.variant(:thumb).blob, users(:david).avatar_thumbnail.blob
@@ -16,7 +17,8 @@ class User::AvatarTest < ActiveSupport::TestCase
   end
 
   test "allows valid image content types" do
-    users(:david).avatar.attach(io: File.open(file_fixture("moon.jpg")), filename: "test.jpg")
+    blob = ActiveStorage::Blob.create_and_upload!(io: File.open(file_fixture("moon.jpg")), filename: "test.jpg", content_type: "image/jpeg")
+    users(:david).avatar.attach(blob)
 
     assert users(:david).valid?
   end
@@ -27,4 +29,22 @@ class User::AvatarTest < ActiveSupport::TestCase
     assert_not users(:david).valid?
     assert_includes users(:david).errors[:avatar], "must be a JPEG, PNG, GIF, or WebP image"
   end
+
+  test "thumb variant is processed immediately on attachment" do
+    # Create blob separately to ensure file is uploaded before variant processing.
+    #
+    # Root cause: When ActiveStorage::Record uses `connects_to` for read replica support
+    # (as in SAAS mode), it creates a separate connection pool from application models.
+    # Since after_commit callbacks are tracked per connection pool, the callback order
+    # between User's pool (upload) and Attachment's pool (create_variants) isn't guaranteed.
+    # In MySQL/SAAS mode, the Attachment callback fires before the file is uploaded.
+    blob = ActiveStorage::Blob.create_and_upload!(
+      io: File.open(file_fixture("avatar.png")),
+      filename: "avatar.png",
+      content_type: "image/png"
+    )
+    users(:david).avatar.attach(blob)
+
+    assert users(:david).avatar.variant(:thumb).processed?
+  end
 end