feat(pi-subagents): 重新启用子 Agent 并使用独立的子 Agent 提示词

- 根包恢复 file:./pi-subagents 依赖与 extensions/subagents.ts 加载
  （排在 permission-system 之后、Tool Search 之前），并刷新根锁文件；
  Agent / get_subagent_result / steer_subagent 权限设为 allow，
  子 Agent 内的实际操作仍逐个经权限系统并转发主会话。
- 新增 config/prompt/subagent/：执行者角色 preamble 与组合包自带的
  general-purpose / Explore / Plan 定义（替换上游内置，去掉 bash find
  冲突规则与写死的 Haiku 模型）。
- pi-subagents 新增 basePrompt / bundledAgentsDir / excludedExtensionPaths
  选项：子 Agent 不再嵌入父会话提示词，身份标记置于开头；子会话排除
  pi-ask-user。未传选项时保持上游行为。
- system-prompt.ts：customPrompt 自带开场白时不再覆盖（修复子 Agent 角色
  与 <active_agent> 身份被抹掉）；仅凭 customPrompt 上的 <active_agent>
  识别子会话，routing 规则支持 scope，sections 支持 subagentExclude
  （子会话去掉 memory_policy 与 chrome_profile_bridge）。
- pi-hermes-memory：子会话只读，记忆/skill 写入工具返回错误，后台整理、
  纠错检测、会话 flush 与索引写入全部跳过。

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

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

extensions/system-prompt.ts

@@ -4,6 +4,7 @@ import { dirname, resolve } from "node:path";
 
 import {
 	applyToolCatalog,
+	isSubagentCustomPrompt,
 	loadRoutingRules,
 	loadSectionsConfig,
 	loadToolCatalog,
@@ -23,8 +24,11 @@ export function getSystemPromptDumpPath(cwd: string): string {
 	return resolve(cwd, DUMP_RELATIVE_PATH);
 }
 
-/** The options object as Pi 1.3 normalizes it; the vendored types predate `sections`/`forceSystemPrompt`. */
-type RuntimePromptOptions = MutablePromptOptions & { forceSystemPrompt?: string };
+/** The options object as Pi 1.3 normalizes it; `MutablePromptOptions` omits `forceSystemPrompt`/`customPrompt`. */
+type RuntimePromptOptions = MutablePromptOptions & {
+	forceSystemPrompt?: string;
+	customPrompt?: string;
+};
 
 /**
  * Injectable seams so the composer can be exercised under `node --test`
@@ -105,6 +109,12 @@ export function createSystemPromptComposer(deps: SystemPromptComposerDeps = {}):
 			return undefined;
 		}
 
+		// A subagent session is identified by its customPrompt carrying the
+		// pi-subagents <active_agent/> tag — never by the rendered prompt, which
+		// a main session may legitimately contain the literal tag inside.
+		const isSubagent = isSubagentCustomPrompt(options?.customPrompt);
+		const audience = isSubagent ? "subagent" : "main";
+
 		let routingText = "";
 		if (options) {
 			const missing = applyToolCatalog(options, catalog);
@@ -115,14 +125,19 @@ export function createSystemPromptComposer(deps: SystemPromptComposerDeps = {}):
 					ctx.ui.notify(`以下工具未在 config/prompt/tools.jsonc 登记：${missing.join(", ")}`, "warning");
 				}
 			}
-			routingText = renderRouting(routing.rules, options.selectedTools);
+			routingText = renderRouting(routing.rules, options.selectedTools, audience);
 			options.sections ??= {};
+			if (isSubagent) {
+				for (const name of sections.subagentExclude) {
+					delete options.sections[name];
+				}
+			}
 			if (routingText.length > 0) {
 				options.sections.tool_routing = routingText;
 			}
 			options.sections = orderSections(options.sections, sections.order);
 		} else {
-			routingText = renderRouting(routing.rules, undefined);
+			routingText = renderRouting(routing.rules, undefined, audience);
 		}
 
 		let rendered = event.systemPrompt;
@@ -132,7 +147,11 @@ export function createSystemPromptComposer(deps: SystemPromptComposerDeps = {}):
 			rendered += `\n\n<tool_routing>\n${routingText}\n</tool_routing>`;
 		}
 
-		const final = preamble ? spliceCover(rendered, preamble) : rendered;
+		// A non-empty customPrompt (pi-subagents agent prompt, SYSTEM.md) owns
+		// the whole preamble — including identities like <active_agent/> that
+		// the permission system reads — so the bundle cover must not replace it.
+		const ownsPreamble = typeof options?.customPrompt === "string" && options.customPrompt.length > 0;
+		const final = preamble && !ownsPreamble ? spliceCover(rendered, preamble) : rendered;
 		lastComposed = final;
 		return { systemPrompt: final };
 	}