feat(pi-worktree): 新增斜杠命令 git worktree 管理扩展

提供 /wt（别名 /worktree）一键拆分/合并：
- /wt new 建 worktree 后经 SessionManager.forkFrom + switchSession
  迁移会话 cwd，历史上下文保留；合并/切换同理
- /wt merge 先确认再 rebase 到来源分支、默认 --ff-only（可选
  --squash），来源改动用 stash 兜底，冲突可中止或保留后用
  /wt merge --continue / --abort 处理，永不 push
- 来源 checkout 的 .pi/worktree.json 声明环境复刻（copy/link/env/
  postCreate），确认框先展示计划再执行；postCreate 仅在项目已信任
  时以 argv 形式 execFile，失败可 /wt reopen 增量重跑
- 登记文件 <agentDir>/pi-worktree/state.json 原子写入并加锁
  串行化；会话切换后向模型注入 cwd 变更提示；未被 .gitignore
  覆盖的软链/环境文件写入 .git/info/exclude 防止误提交
- 仅注册用户显式触发的斜杠命令，不暴露模型可调用工具

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

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

pi-worktree/test/session.test.ts

@@ -0,0 +1,147 @@
+import assert from "node:assert/strict";
+import { CURRENT_SESSION_VERSION, SessionManager } from "@earendil-works/pi-coding-agent";
+import { existsSync } from "node:fs";
+import { mkdir, mkdtemp, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join, resolve } from "node:path";
+import test from "node:test";
+
+import { prepareSessionForCwd, switchToCwd } from "../src/session.ts";
+
+interface FakeContext {
+	sessionManager: { getSessionFile(): string | undefined };
+}
+
+function fakeCtx(getSessionFile: () => string | undefined): FakeContext {
+	return { sessionManager: { getSessionFile } };
+}
+
+test("prepareSessionForCwd forks an existing session file into the target cwd", async (t) => {
+	const agentDir = await mkdtemp(join(tmpdir(), "pi-worktree-agent-"));
+	const previous = process.env.PI_CODING_AGENT_DIR;
+	process.env.PI_CODING_AGENT_DIR = agentDir;
+	t.after(() => {
+		if (previous === undefined) delete process.env.PI_CODING_AGENT_DIR;
+		else process.env.PI_CODING_AGENT_DIR = previous;
+	});
+
+	const root = await mkdtemp(join(tmpdir(), "pi-worktree-session-"));
+	const sourceCwd = join(root, "source");
+	const targetCwd = join(root, "target");
+	await mkdir(sourceCwd, { recursive: true });
+	await mkdir(targetCwd, { recursive: true });
+
+	// Hand-written session file: header plus one user message entry.
+	const sessionDir = join(root, "sessions");
+	await mkdir(sessionDir, { recursive: true });
+	const file = join(sessionDir, "source-session.jsonl");
+	const header = {
+		type: "session",
+		version: CURRENT_SESSION_VERSION,
+		id: "11111111-1111-4111-8111-111111111111",
+		timestamp: new Date().toISOString(),
+		cwd: sourceCwd,
+	};
+	const message = {
+		type: "message",
+		id: "22222222-2222-4222-8222-222222222222",
+		parentId: null,
+		timestamp: new Date().toISOString(),
+		message: {
+			role: "user",
+			content: [{ type: "text", text: "hello" }],
+			timestamp: Date.now(),
+		},
+	};
+	await writeFile(file, `${JSON.stringify(header)}\n${JSON.stringify(message)}\n`, "utf8");
+
+	const newFile = prepareSessionForCwd(fakeCtx(() => file), targetCwd);
+	assert.ok(existsSync(newFile));
+	assert.notEqual(newFile, file);
+
+	const opened = SessionManager.open(newFile);
+	assert.equal(opened.getCwd(), resolve(targetCwd));
+	const entries = opened.getEntries();
+	assert.ok(entries.some((e) => e.type === "message"), "forked session keeps the history");
+});
+
+test("prepareSessionForCwd writes a minimal session file when none exists yet", async (t) => {
+	const agentDir = await mkdtemp(join(tmpdir(), "pi-worktree-agent-"));
+	const previous = process.env.PI_CODING_AGENT_DIR;
+	process.env.PI_CODING_AGENT_DIR = agentDir;
+	t.after(() => {
+		if (previous === undefined) delete process.env.PI_CODING_AGENT_DIR;
+		else process.env.PI_CODING_AGENT_DIR = previous;
+	});
+
+	const targetCwd = await mkdtemp(join(tmpdir(), "pi-worktree-target-"));
+	const newFile = prepareSessionForCwd(fakeCtx(() => undefined), targetCwd);
+	assert.ok(existsSync(newFile));
+	assert.equal(SessionManager.open(newFile).getCwd(), resolve(targetCwd));
+});
+
+test("switchToCwd appends a cwd-change notice before running the callback", async (t) => {
+	const agentDir = await mkdtemp(join(tmpdir(), "pi-worktree-agent-"));
+	const previous = process.env.PI_CODING_AGENT_DIR;
+	process.env.PI_CODING_AGENT_DIR = agentDir;
+	t.after(() => {
+		if (previous === undefined) delete process.env.PI_CODING_AGENT_DIR;
+		else process.env.PI_CODING_AGENT_DIR = previous;
+	});
+
+	const targetCwd = await mkdtemp(join(tmpdir(), "pi-worktree-target-"));
+	const order: string[] = [];
+	const sent: { message: unknown; options: unknown }[] = [];
+	const replacement = {
+		sendMessage: async (message: unknown, options: unknown) => {
+			order.push("sendMessage");
+			sent.push({ message, options });
+		},
+	};
+	const ctx = {
+		cwd: "/a",
+		waitForIdle: async () => undefined,
+		sessionManager: { getSessionFile: () => undefined },
+		switchSession: async (_file: string, opts: { withSession: (c: unknown) => Promise<void> }) => {
+			await opts.withSession(replacement);
+			return { cancelled: false };
+		},
+	};
+
+	const switched = await switchToCwd(ctx as never, targetCwd, async () => {
+		order.push("withSession");
+	});
+	assert.equal(switched.cancelled, false);
+	assert.deepEqual(order, ["sendMessage", "withSession"]);
+	assert.equal(sent.length, 1);
+	const { message, options } = sent[0] as { message: { customType?: string; content?: string; display?: boolean }; options: unknown };
+	assert.equal(message.customType, "pi-worktree");
+	assert.equal(message.display, true);
+	assert.ok(message.content?.includes("/a"), "notice names the previous cwd");
+	assert.ok(message.content?.includes(targetCwd), "notice names the new cwd");
+	assert.equal(options, undefined);
+});
+
+test("switchToCwd skips the notice when the cwd did not change", async (t) => {
+	const agentDir = await mkdtemp(join(tmpdir(), "pi-worktree-agent-"));
+	const previous = process.env.PI_CODING_AGENT_DIR;
+	process.env.PI_CODING_AGENT_DIR = agentDir;
+	t.after(() => {
+		if (previous === undefined) delete process.env.PI_CODING_AGENT_DIR;
+		else process.env.PI_CODING_AGENT_DIR = previous;
+	});
+
+	const targetCwd = await mkdtemp(join(tmpdir(), "pi-worktree-target-"));
+	let sent = 0;
+	const ctx = {
+		cwd: targetCwd,
+		waitForIdle: async () => undefined,
+		sessionManager: { getSessionFile: () => undefined },
+		switchSession: async (_file: string, opts: { withSession: (c: unknown) => Promise<void> }) => {
+			await opts.withSession({ sendMessage: async () => sent++ });
+			return { cancelled: false };
+		},
+	};
+	await switchToCwd(ctx as never, targetCwd, async () => undefined);
+	assert.equal(sent, 0);
+});