feat: 系统提示词改为单一入口统一管理

多个扩展各自整段改写系统提示词并按加载顺序接力，任一扩展定死提示词后
其余只能做字符串手术，且各上游的工具说明与组合包实际工具格局冲突。

- 新增 extensions/system-prompt.ts 作为唯一出口（加载列表最后），按
  config/prompt/（preamble.md、tools.jsonc、routing.jsonc、sections.jsonc）
  组合开场白、工具简介/规则与 <tool_routing> 分区；替代原封面与
  tool-routing 扩展，/dump-system-prompt 输出最终提示词。
- pi-chrome、pi-ssh、pi-hermes-memory 改为写命名分区，pi-rtk-optimizer
  改写 promptGuidelines，pi-permission-system 直接过滤结构化 skills，
  均不再返回 systemPrompt；pi-chrome 未授权时不再每轮冻结提示词。
- 新增 prompt-guard 代理加载第三方扩展（Hashline、FFF、LSP、
  context-mode）：拦截直接改写提示词并按目录覆盖工具说明；context-mode
  去掉与组合包路由冲突的锚点段，保留记忆与恢复快照。
- 消除冲突：bash 简介不再建议 grep/find；Hashline edit 不再称可用 grep
  锚点、不再介绍已关闭的 replace_text；context-mode 读写/网页路由提示。
- 守门测试：工具目录覆盖率、禁用用法检查、context-mode 上游原文锁定；
  AGENTS.md 新增「系统提示词单一所有权」。

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

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

tests/extension-load.test.ts

@@ -1,4 +1,5 @@
 import assert from "node:assert/strict";
+import { existsSync } from "node:fs";
 import { mkdir, mkdtemp, readFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { dirname, join, resolve } from "node:path";
@@ -154,17 +155,44 @@ test("all package extensions load together without global registration conflicts
 		packageJson.pi.extensions.includes("./pi-hermes-memory/src/index.ts"),
 		"the bundle must load the locally maintained Hermes memory extension",
 	);
-	// The cover must rewrite the prompt before tool-routing flattens it into a forced prompt;
-	// once flattened, later handlers cannot restore the section structure.
+	// extensions/system-prompt.ts is the bundle's single system-prompt owner and
+	// must run after every tool-registration extension (including Tool Search)
+	// so it sees the complete tool set and any contributed sections.
+	assert.equal(
+		packageJson.pi.extensions.at(-1),
+		"./extensions/system-prompt.ts",
+		"the single system-prompt owner must be the last loaded extension",
+	);
 	assert.ok(
+		packageJson.pi.extensions.includes("./extensions/context-mode.ts"),
+		"Context Mode must load through the bundle's prompt-guarded wrapper",
+	);
+	assert.equal(
+		packageJson.pi.extensions.some((entry) => entry.includes("context-mode/build/")),
+		false,
+		"the raw Context Mode adapter must not be loaded alongside the wrapper",
+	);
+	assert.equal(
 		packageJson.pi.extensions.includes("./extensions/system-prompt-cover.ts"),
-		"the bundle must load the system prompt cover extension",
+		false,
+		"the retired system-prompt cover must not be loaded",
 	);
-	assert.ok(
-		packageJson.pi.extensions.indexOf("./extensions/system-prompt-cover.ts") <
-			packageJson.pi.extensions.indexOf("./extensions/tool-routing.ts"),
-		"the system prompt cover must run before tool-routing forces the prompt",
+	assert.equal(
+		packageJson.pi.extensions.includes("./extensions/tool-routing.ts"),
+		false,
+		"the retired tool-routing extension must not be loaded",
 	);
+	for (const retired of [
+		"extensions/system-prompt-cover.ts",
+		"extensions/system-prompt-cover-config.ts",
+		"extensions/tool-routing.ts",
+	]) {
+		assert.equal(
+			existsSync(join(repositoryRoot, retired)),
+			false,
+			`${retired} was superseded by extensions/system-prompt.ts and must be deleted`,
+		);
+	}
 	assert.equal(packageJson.dependencies["pi-hermes-memory"], "file:./pi-hermes-memory");
 	assert.ok(
 		packageJson.files.includes("pi-hermes-memory"),