feat(pi-web-search): 统一 web_search/web_fetch 并由主模型路由搜索厂商

7 个按厂商命名的搜索工具收敛为 2 个统一工具，schema 与提示词不再暴露
provider 概念：web_search 由当前主模型按内置规则在 Tavily/Exa/Keenable
间路由（会话内 LRU 缓存，失败按可用性降级），web_fetch 固定走 Exa 并
静默降级。三家均改为纯 fetch 直连——Exa 直接对 mcp.exa.ai 发 JSON-RPC
并缓存会话，彻底移除 pi-mcp-adapter、@tavily/pi-extension 与
@keenable/pi-search 依赖。

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

pi-web-search/README.md

@@ -0,0 +1,35 @@
+# pi-web-search
+
+Unified web search and fetch for Pi. The main model only ever sees two tools —
+`web_search` and `web_fetch` — provider selection happens inside the extension.
+
+- `web_search(query, max_results?, site?, published_after?, published_before?, depth?)`
+  routes each query to Tavily, Exa, or Keenable using the session's current main
+  model (`ctx.model` + `ctx.modelRegistry.complete`), guided by per-provider
+  rules. Results include `details.provider` / `details.routedBy` for debugging.
+- `web_fetch(urls, max_characters?)` always reads pages via Exa
+  (`web_fetch_exa`), degrading silently to Keenable then Tavily.
+
+## Providers (`clients/`)
+
+Plain `fetch` calls — no MCP adapter, no upstream extension wrappers:
+
+- `clients/tavily.ts` — `POST api.tavily.com/search|extract`, Bearer key.
+  Requires `TAVILY_API_KEY`.
+- `clients/keenable.ts` — `api.keenable.ai`, keyless `/public` endpoints by
+  default, `KEENABLE_API_KEY` raises rate limits. Adapted from
+  `@keenable/pi-search`.
+- `clients/exa.ts` — JSON-RPC over `mcp.exa.ai/mcp` (Streamable HTTP):
+  `initialize` once, cache `mcp-session-id`, `tools/call` per request, re-init
+  on session expiry. `EXA_API_KEY` optional (`x-api-key` header).
+
+Keys are loaded from `~/.config/my-pi/search.env` by `extensions/search-config.ts`
+(written by `search_config.sh`); explicit environment variables win.
+
+## Routing
+
+`router.ts` asks the current model to answer with exactly one provider name,
+given a prompt containing the per-provider strengths and the query's requested
+filters. Decisions are cached per session (LRU, 32 entries). Failure paths are
+deterministic: an unroutable answer or a dead provider falls back across the
+remaining available providers — never a heuristic choice over the model.