fix: stream attachment handling in workers (#12870)

We’ve been watching Sidekiq workers climb from ~600 MB at boot to
1.4–1.5 GB after an hour whenever attachment-heavy jobs run. This PR is
an experiment to curb that growth by streaming attachments instead of
loading the whole blob into Ruby: reply-mailer inline attachments,
Telegram uploads, and audio transcriptions now read/write in chunks. If
this keeps RSS stable in production we’ll keep it; otherwise we’ll roll
it back and keep digging

spec/enterprise/services/captain/llm/pdf_processing_service_spec.rb

@@ -28,13 +28,14 @@ RSpec.describe Captain::Llm::PdfProcessingService do
     context 'when uploading PDF to OpenAI' do
       let(:mock_client) { instance_double(OpenAI::Client) }
       let(:pdf_content) { 'PDF content' }
+      let(:blob_double) { instance_double(ActiveStorage::Blob) }
+      let(:pdf_file) { instance_double(ActiveStorage::Attachment) }
 
       before do
         allow(document).to receive(:openai_file_id).and_return(nil)
-
-        # Use a simple double for ActiveStorage since it's a complex Rails object
-        pdf_file = double('pdf_file', download: pdf_content) # rubocop:disable RSpec/VerifiedDoubles
         allow(document).to receive(:pdf_file).and_return(pdf_file)
+        allow(pdf_file).to receive(:blob).and_return(blob_double)
+        allow(blob_double).to receive(:open).and_yield(StringIO.new(pdf_content))
 
         allow(OpenAI::Client).to receive(:new).and_return(mock_client)
         # Use a simple double for OpenAI::Files as it may not be loaded

spec/jobs/data_import_job_spec.rb

@@ -15,8 +15,11 @@ RSpec.describe DataImportJob do
 
   describe 'retrying the job' do
     context 'when ActiveStorage::FileNotFoundError is raised' do
+      let(:import_file_double) { instance_double(ActiveStorage::Blob) }
+
       before do
-        allow(data_import.import_file).to receive(:download).and_raise(ActiveStorage::FileNotFoundError)
+        allow(data_import).to receive(:import_file).and_return(import_file_double)
+        allow(import_file_double).to receive(:open).and_raise(ActiveStorage::FileNotFoundError)
       end
 
       it 'retries the job' do
@@ -158,7 +161,9 @@ RSpec.describe DataImportJob do
       end
 
       before do
-        allow(data_import.import_file).to receive(:download).and_return(invalid_csv_content)
+        import_file_double = instance_double(ActiveStorage::Blob)
+        allow(data_import).to receive(:import_file).and_return(import_file_double)
+        allow(import_file_double).to receive(:open).and_yield(StringIO.new(invalid_csv_content))
       end
 
       it 'does not import any data and handles the MalformedCSVError' do

spec/lib/integrations/slack/send_on_slack_service_spec.rb

@@ -206,6 +206,21 @@ describe Integrations::Slack::SendOnSlackService do
         expect(message.attachments.count).to eq 2
       end
 
+      it 'streams attachment blobs and uploads only once' do
+        expect(slack_client).to receive(:chat_postMessage).and_return(slack_message)
+
+        attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
+        attachment.file.attach(io: Rails.root.join('spec/assets/avatar.png').open, filename: 'avatar.png', content_type: 'image/png')
+        blob = attachment.file.blob
+        allow(blob).to receive(:open).and_call_original
+
+        expect(blob).to receive(:open).and_call_original
+        expect(slack_client).to receive(:files_upload_v2).once.and_return(file_attachment)
+
+        message.save!
+        builder.perform
+      end
+
       it 'handles file upload errors gracefully' do
         expect(slack_client).to receive(:chat_postMessage).with(
           channel: hook.reference_id,