feat(pi-overflow): 新增统一的新工具结果展示截断扩展

此前截断分散在多层且互相冲突：Pi bash 保留尾部 50KB，RTK 兜底截断又只留
开头 12000 字符（砍掉报错与完整输出路径），pi-chrome 截开头 30K，web_fetch
各 provider 不一致。新扩展统一负责"新结果给模型看多少"：
- capture.ts 最先加载暂存原文，index.ts 最后加载（system-prompt 之前）
- 超过 24K 字符时原文落盘 <agentDir>/my-pi/pi-overflow/（700/600、原子写），
  优先取 bash fullOutputPath 完整文件；模型看到 头 + 中段信号行 + 尾 的有界
  视图，行号基于落盘原文、结尾永远可见
- overflow_query：按 id 正则搜索、行区间、jsonPath 只读查询，id 校验防穿越
- 收编：RTK truncate 默认关闭、删除 pi-chrome truncateText、web_fetch 默认
  每页 20000（上限 100000）、web_search max_results 限定 1–20
- pi-compaction 遮蔽带 details.overflow.id 的结果时在占位符提示 overflow_query
- 登记 tools.jsonc / routing / 权限 allow / tool-search 常驻与分组

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

pi-overflow/README.md

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+# pi-overflow
+
+Bounded display for oversized tool results. When a tool result exceeds
+`thresholdChars`, pi-overflow persists the full original to disk and shows the
+model a deterministic view — head lines, signal lines (error/fail/warn/…), and
+tail lines — plus an `overflow_query` tool to search or read the stored
+original by id.
+
+## Two-stage load order
+
+- `capture.ts` — **first** in `pi.extensions`. A `tool_result` handler that
+  never modifies anything; it stashes the untouched original text in
+  `globalThis[Symbol.for("my-pi.pi-overflow.stash.v1")]` (capacity 64) so the
+  bound stage can still reach the pre-RTK original.
+- `index.ts` — **last** content extension, right before `system-prompt.ts`.
+  Its `tool_result` handler sees the final text after every other handler
+  (RTK semantic compaction included) has run, then:
+  - resolves the *original*: `details.fullOutputPath` file (streamed, capped
+    at `maxEntryBytes` head+tail) → stashed raw text → current text;
+  - if the current text still exceeds `thresholdChars`, replaces it with the
+    bounded view **built from the stored file** — line numbers and totals in
+    the view are exactly what `overflow_query` will read, even when RTK or
+    bash already cut the in-context text (file sources are scanned
+    line-by-line in a stream, never held in memory);
+  - if the current text fits but the original did not (an earlier extension
+    already cut it), keeps the text and appends a one-line
+    `[pi-overflow id=…]` recovery marker;
+  - preserves image parts and `structuredContent`, and merges
+    `details.overflow = { id, totalLines, totalBytes, truncated }` into the
+    existing details.
+- Exempt tools (`read`, `edit`, `write`, `overflow_query`,
+  `ask_user_question`) and nested calls (`parentToolCallId`) are never
+  touched.
+
+## Stored originals
+
+`<agentDir>/my-pi/pi-overflow/<id>.txt` + `<id>.json` metadata, where
+`id = sha1(sessionId + "\0" + toolCallId)[0:12]`. Directories are `0700`,
+files `0600`, writes are atomic. `session_start` cleans entries older than
+`retentionDays` and evicts oldest-first past `maxStoreBytes`.
+
+## `overflow_query`
+
+- `id` (required, `^[0-9a-f]{12}$` — path traversal safe)
+- `search` — case-insensitive regex; hits come back with `context` lines and
+  adjacent hits merge; capped by `maxResults`
+- `lines: { start, end }` — 1-based inclusive line range
+- `jsonPath` — dot/bracket path into stored JSON (`a.b[3].c`)
+- No selector → metadata + first-screen view. Output is always bounded by
+  `thresholdChars` and reports whether it was truncated.
+
+## Configuration
+
+`config/pi-overflow.json` inside the installed bundle. Every field is
+validated independently and falls back to its default; an uncompilable
+`signalPattern` falls back to the default pattern (case-insensitive).
+
+## Development
+
+```sh
+npm test        # node --test test/*.test.ts
+npm run check   # strip-types syntax check + tests
+```
+
+Tests inject a temporary store root — they never write to a real agent
+directory.