fix(whatsapp): log manual transfer only for embedded signup migrations (#15032)

The `[WHATSAPP_MANUAL_TRANSFER] success` log introduced in #14975 to
track embedded signup → manual migrations was firing on any WhatsApp
credential change — including routine `api_key` rotations on inboxes
that were already manually configured — inflating the migration count.
The log now fires only for the actual migration, and uses a new tag so
log searches don't match the older over-counted entries.

## How to reproduce

1. On a manually configured WhatsApp Cloud inbox, update the API key
from inbox settings → Configuration.
2. Before this change, the app log records a `[WHATSAPP_MANUAL_TRANSFER]
success` line even though no migration happened; after this change it
stays silent.
3. Switching an embedded signup inbox to manual setup still logs the
migration (now as `[WHATSAPP_EMBEDDED_TO_MANUAL] success`).

## What changed

- `Channel::Whatsapp#log_credentials_transfer` now keys off the
migration's unique signal — `provider_config['source']` changing from
`embedded_signup` to absent — instead of diffing credential keys.
- Renamed the log tag from `WHATSAPP_MANUAL_TRANSFER` to
`WHATSAPP_EMBEDDED_TO_MANUAL` (success and failure lines) so the
corrected entries are searchable without matching pre-fix false
positives.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Muhsin <12408980+muhsin-k@users.noreply.github.com>

app/models/channel/whatsapp.rb

@@ -101,6 +101,13 @@ class Channel::Whatsapp < ApplicationRecord
     end
   end
 
+  # Whether the pending (unsaved) provider_config change drops the embedded_signup
+  # source marker, i.e. this save is an embedded signup → manual setup transfer.
+  def embedded_to_manual_transfer_pending?
+    before, after = provider_config_change
+    before&.dig('source') == 'embedded_signup' && after['source'] != 'embedded_signup'
+  end
+
   def mark_message_templates_updated
     # rubocop:disable Rails/SkipsModelValidations
     update_column(:message_templates_last_updated, Time.zone.now)
@@ -130,13 +137,14 @@ class Channel::Whatsapp < ApplicationRecord
     errors.add(:provider_config, 'Invalid Credentials') unless provider_service.validate_provider_config?
   end
 
-  # Logs only credential changes, so config-only saves (e.g. calling toggles) stay silent.
+  # Logs only the embedded signup → manual migration (the save drops the
+  # embedded_signup source marker), so credential rotations on inboxes that are
+  # already manual stay silent.
   def log_credentials_transfer
     before, after = saved_change_to_provider_config
-    keys = %w[api_key phone_number_id business_account_id]
-    return if before.nil? || before.values_at(*keys) == after.values_at(*keys)
+    return unless before&.dig('source') == 'embedded_signup' && after['source'] != 'embedded_signup'
 
-    Rails.logger.info("[WHATSAPP_MANUAL_TRANSFER] success account_id=#{account_id} channel_id=#{id}")
+    Rails.logger.info("[WHATSAPP_EMBEDDED_TO_MANUAL] success account_id=#{account_id} channel_id=#{id}")
   end
 
   def perform_webhook_setup

app/services/whatsapp/providers/whatsapp_cloud_service.rb

@@ -94,12 +94,12 @@ class Whatsapp::Providers::WhatsappCloudService < Whatsapp::Providers::BaseServi
 
   private
 
-  # Only credential updates on existing channels are transfer attempts; creation failures are regular setup errors. Returns false.
+  # Only saves dropping the embedded_signup source marker are transfer attempts; creation/rotation failures are setup errors. Returns false.
   def log_transfer_failure(check, response)
-    return false unless whatsapp_channel.persisted? && whatsapp_channel.provider_config_changed?
+    return false unless whatsapp_channel.embedded_to_manual_transfer_pending?
 
     error_message = response.parsed_response.is_a?(Hash) ? response.parsed_response.dig('error', 'message') : nil
-    Rails.logger.warn("[WHATSAPP_MANUAL_TRANSFER] failure account_id=#{whatsapp_channel.account_id} channel_id=#{whatsapp_channel.id} " \
+    Rails.logger.warn("[WHATSAPP_EMBEDDED_TO_MANUAL] failure account_id=#{whatsapp_channel.account_id} channel_id=#{whatsapp_channel.id} " \
                       "check=#{check} http_status=#{response.code} meta_error=#{error_message}")
     false
   end