Error Classification, Deadlock Rescue & Dead Code Cleanup

What Was Built

• Transient vs fatal error classification in FaviconFetchJob and DownloadContentImagesJob
• TRANSIENT_ERRORS constant (Timeout::Error, Errno::ETIMEDOUT, Faraday::TimeoutError, Faraday::ConnectionFailed, Net::OpenTimeout, Net::ReadTimeout) in both jobs
• Transient errors re-raise for framework retry; fatal errors handled gracefully
• Per-image fatal errors in DownloadContentImagesJob log at warn level with image URL
• rescue_from ActiveRecord::Deadlocked with jitter retry added to ScrapeItemJob, ItemCleanupJob, LogCleanupJob, ScheduleFetchesJob
• ScrapeItemJob log levels fixed: error stages use :error level, normal stages use :info

Commits

• 554f8cd test(04-02): add error classification tests for FaviconFetchJob and DownloadContentImagesJob
• 19bb3b8 feat(04-02): add transient vs fatal error classification to FaviconFetchJob
• 6bcd0ac feat(04-02): add transient vs fatal error classification to DownloadContentImagesJob
• 911c17e fix(04-02): add deadlock rescue to 4 jobs, fix ScrapeItemJob log levels

Tasks Completed

1. Write tests for error classification (TDD red) -- 4 new tests across 2 files
2. Implement error classification in FaviconFetchJob -- TRANSIENT_ERRORS constant, separate rescue clause
3. Implement error classification in DownloadContentImagesJob -- TRANSIENT_ERRORS, per-image warn logging
4. Deadlock rescue + log level fixes -- rescue_from added to 4 jobs, ScrapeItemJob log level dynamic dispatch
5. Verify -- 1491 runs, 4537 assertions, 0 failures; 465 files, 0 RuboCop offenses

Files Modified

• app/jobs/source_monitor/favicon_fetch_job.rb -- TRANSIENT_ERRORS constant, transient rescue clause, log_transient_error method
• app/jobs/source_monitor/download_content_images_job.rb -- TRANSIENT_ERRORS constant, transient rescue in per-image loop, log_image_error method
• app/jobs/source_monitor/scrape_item_job.rb -- rescue_from Deadlocked, dynamic log level
• app/jobs/source_monitor/item_cleanup_job.rb -- rescue_from Deadlocked with jitter retry
• app/jobs/source_monitor/log_cleanup_job.rb -- rescue_from Deadlocked with jitter retry
• app/jobs/source_monitor/schedule_fetches_job.rb -- rescue_from Deadlocked with jitter retry
• app/jobs/source_monitor/import_session_health_check_job.rb -- clarified inline rescue comment
• test/jobs/source_monitor/favicon_fetch_job_test.rb -- 2 new tests (transient re-raise, fatal handling)
• test/jobs/source_monitor/download_content_images_job_test.rb -- 2 new tests (transient re-raise, per-image skip)

Deviations

• DEVN-01: ImportSessionHealthCheckJob inline rescue ActiveRecord::Deadlocked; raise was NOT dead code as the plan stated. It prevents rescue StandardError from swallowing deadlocks before rescue_from can catch them. Retained with clarified comment instead of removing.