Phase 1: Backend Fixes -- Verification

Test Results

• Targeted tests: 97 runs, 305 assertions, 0 failures, 0 errors
• RuboCop: 5 files inspected, 0 offenses

Plan 01: HTTP Client Hardening -- PASS

• DEFAULT_USER_AGENT = "Mozilla/5.0 (compatible; SourceMonitor/VERSION)" in http.rb and http_settings.rb
• Accept header prepends text/html
• Accept-Language: en-US,en;q=0.9 and DNT: 1 added to default_headers
• Referer header added from source.website_url in FeedFetcher#request_headers
• 4 new tests added (UA, Accept-Language/DNT, Referer present, Referer blank)

Plan 02: Health Check Status Transition -- PASS

• DEGRADED_STATUSES = %w[declining critical warning] added to SourceHealthCheckJob
• trigger_fetch_if_degraded called after broadcast_outcome
• Enqueues FetchFeedJob.perform_later(source.id, force: true) on degraded sources
• 5 new tests (declining, critical, warning, healthy exclusion, failed check exclusion)

Plan 03: Remove Default Scrape Limit -- PASS

• DEFAULT_MAX_IN_FLIGHT changed from 25 to nil
• rate_limit_exhausted? handles nil correctly (returns [false, nil])
• BulkResultPresenter handles nil limit in rate_limited message
• 3 new tests (nil default bypass, nil limit message, explicit limit message)

Cross-Plan Integration

• No file conflicts between plans (disjoint file sets verified)
• All scraping tests pass with new nil default
• Health check tests pass with updated HTTP headers