Bug 1: Reddit 403 due to short User-Agent in proxy test
Root cause: configure proxy test used 'Mozilla/5.0' (too short, Reddit rejects)
Fix: use full UA string matching the channel implementation
Bug 2: Reddit URL parsing broke on trailing slashes
Root cause: url.rstrip('/') + '.json' mangled URLs with query params
Fix: properly parse URL, clean path, reconstruct json URL
Bug 3: Reddit 403 without proxy showed raw HTTP error
Root cause: no error handling for 403/429 responses
Fix: friendly message suggesting proxy setup + Exa search alternative
Bug 4: XiaoHongShu without cookie showed Jina Reader 451 error
Root cause: fallback to Jina Reader which can't access XHS (legal block)
Fix: show clear message about needing cookies with setup instructions
Bug 5: Empty search query caused raw 422 API error
Root cause: no input validation before API call
Fix: check for empty query, show friendly message
All 36 unit tests passing.