Plan 2: Source Deletion Fix

Investigate and fix the 500 error when deleting sources, particularly when host apps extend engine models with additional FK references.

Tasks

Task 1: Investigate the destroy cascade

Files: app/models/source_monitor/source.rb, app/controllers/source_monitor/sources_controller.rb

Examine the full dependent: :destroy chain on Source:

• has_many :all_items (dependent setting?)
• has_many :fetch_logs (dependent setting?)
• has_many :scrape_logs (dependent setting?)
• has_many :health_check_logs (dependent setting?)
• has_many :log_entries (dependent setting?)
• has_one_attached :favicon (Active Storage)

Check if any association is missing dependent: :destroy or if the ordering causes FK violations. Pay special attention to:

1. Active Storage favicon attachment cleanup
2. Whether items have their own dependent associations that cascade further
3. Whether the engine properly handles host-app-added associations

Task 2: Fix the destroy cascade

Based on investigation findings:

• Ensure all associations have proper dependent: options
• Use dependent: :destroy_async for large collections if appropriate
• Add a before_destroy callback to handle cleanup ordering if needed
• Ensure Active Storage favicon is properly cleaned up

Task 3: Add error handling to destroy action

Files: app/controllers/source_monitor/sources_controller.rb

Wrap @source.destroy in proper error handling:

if @source.destroy
  # existing turbo stream / html response
else
  # error response with useful message
end

Also add rescue ActiveRecord::InvalidForeignKey to catch host-app FK violations and provide a helpful error message like "Cannot delete source: other records still reference it."

Task 4: Add tests for destroy action

• Test successful deletion with all dependent records
• Test deletion failure handling (FK violation scenario)
• Test that error messages are user-friendly
• Test both turbo_stream and html response formats

Acceptance Criteria

• Deleting a source with items, logs, and favicon works without error
• FK violations from host app extensions produce a user-friendly error instead of 500
• Both turbo_stream and html response formats handle success and failure
• All existing tests pass plus new destroy tests
• RuboCop zero offenses