Plan 02: Error Classification, Deadlock Rescue & Dead Code Cleanup

Objective

Add transient vs fatal error classification to FaviconFetchJob and DownloadContentImagesJob (S6), add deadlock rescue to jobs that lack it, remove dead code from ImportSessionHealthCheckJob (S1), and fix ScrapeItemJob log levels (S5 partial).

Context

• @.claude/skills/sm-job/SKILL.md -- Job conventions, error handling patterns, deadlock rescue template
• @.claude/skills/tdd-cycle/SKILL.md -- TDD workflow
• FaviconFetchJob (73 lines) catches all StandardError the same way -- timeouts should retry, invalid images should not
• DownloadContentImagesJob (75 lines) silently swallows all errors per-image -- blob/attachment failures should re-raise
• ImportSessionHealthCheckJob has unreachable rescue ActiveRecord::Deadlocked; raise at lines 58-59 (rescue_from at line 13 catches first)
• ScrapeItemJob logs errors at info level instead of warn/error
• 4 jobs missing rescue_from ActiveRecord::Deadlocked: ScheduleFetchesJob, ItemCleanupJob, LogCleanupJob, ScrapeItemJob

Tasks

Task 1: Write tests for error classification (TDD red)

Create/update test files:

• test/jobs/source_monitor/favicon_fetch_job_test.rb: test transient error (Faraday::TimeoutError) re-raises; test fatal error (RuntimeError) calls record_failed_attempt without re-raising
• test/jobs/source_monitor/download_content_images_job_test.rb: test transient error (Faraday::TimeoutError) re-raises entire job; test per-image fatal error (URI::InvalidURIError) skips image and continues

Task 2: Implement error classification in FaviconFetchJob

Modify app/jobs/source_monitor/favicon_fetch_job.rb:

• Add TRANSIENT_ERRORS constant: [Timeout::Error, Errno::ETIMEDOUT, Faraday::TimeoutError, Faraday::ConnectionFailed, Net::OpenTimeout, Net::ReadTimeout].freeze
• Add rescue clause for *TRANSIENT_ERRORS BEFORE the StandardError rescue
• Transient: log at warn level, re-raise (let framework retry)
• Fatal: existing behavior (record_failed_attempt + log_error)

Task 3: Implement error classification in DownloadContentImagesJob

Modify app/jobs/source_monitor/download_content_images_job.rb:

• Add same TRANSIENT_ERRORS constant
• In the per-image loop: rescue *TRANSIENT_ERRORS and re-raise (abort entire job for retry)
• Keep existing rescue StandardError for per-image fatal errors but add warn-level logging with image URL
• Ensure ActiveRecord::Deadlocked rescue remains above both

Task 4: Deadlock rescue + dead code cleanup + log level fixes

Apply to multiple jobs:

• ImportSessionHealthCheckJob: remove dead rescue ActiveRecord::Deadlocked; raise block at lines 58-59
• ScrapeItemJob: add rescue_from ActiveRecord::Deadlocked with jitter retry; change error log level from info to warn/error
• ItemCleanupJob: add rescue_from ActiveRecord::Deadlocked with jitter retry
• LogCleanupJob: add rescue_from ActiveRecord::Deadlocked with jitter retry
• ScheduleFetchesJob: add rescue_from ActiveRecord::Deadlocked with jitter retry

Task 5: Verify

• bin/rails test test/jobs/source_monitor/ -- all job tests pass
• bin/rails test -- full suite passes
• bin/rubocop -- zero offenses
• grep -r "rescue ActiveRecord::Deadlocked" app/jobs/ confirms all jobs have rescue_from or inline rescue