feat(prompt): 搜索引导改为意图→工具的正向指引，multi_grep 按上游保持关闭

真实会话中模型仍用 bash grep -o | sort -u 做抽取，被拒后直接放弃核对；
原提示词只说"不要"，没告诉它抽取/计数、给程序传文件清单、过滤命令输出时该用什么。

- routing：按已知信息选 grep/find（多变体用 grep 正则 alternation），
  codemode + tools.grep 做聚合，bash 文件清单用 git ls-files，
  overflow_query 过滤输出，被拒后改用替代方案继续
- 权限策略：rg/grep/git grep/find/fd 的 deny 附带指向替代工具的 reason
- tools.jsonc：grep/find 新 snippet，补上 codegraph_explore snippet
- FFF 上游标注 multi_grep 有害：wrapper 删除 PI_FFF_MULTIGREP，清理全部引用
- JSONC 测试改用字符串感知的注释剥离（reason 中含 'src/**/*.ts'）

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pi-tool-search/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased — my-pi maintained source
 
 ### Changed
+- Removed `multi_grep` from the `filesystem-navigation` group: the bundle wrapper keeps FFF's upstream `PI_FFF_MULTIGREP` opt-in disabled, so the tool is never registered and the group now covers only `ls`.
 - Pinned Pi's built-in `codemode` (exposure `model-only`) in `alwaysEnabled` so batching several tool calls through one script never depends on a `tool_search` activation; `platformToolPolicy` now also drops tools with `hidden` or `codemode` (script-only) exposure so they can never enter the catalog or the unknown-tools path.
 - Removed the `PI_TOOL_SEARCH_CONFIG_PATH` environment override; the extension reads the bundle `config/tool-search.json`, and tests inject a path through the `createToolSearchExtension({ configPath })` factory.
 - Removed the retired context-mode integration: the `ctx_execute` / `ctx_execute_file` / `ctx_batch_execute` pins left `alwaysEnabled` and the four `context-*` bundle groups were dropped. Large tool results are now bounded by pi-overflow and recoverable through the pinned `overflow_query`.