web_search auto chain Perplexity/Exa/Tavily/Brave/SearXNG/DuckDuckGo with pinned-provider no-fallback, web_fetch with head+tail truncation, codex-home seeding helper (idempotent, never writes keys). Tests: cloud/tests/test_websearch_mcp.py 12/12 (mocked HTTP). Not wired into worker, not deployed, paid backends not live-tested.