fix(sessions): fold Cursor Tasks under Agent Sub-Sessions like Codex

[zephyr110]

Summary

• Routing: Honor Agent Sub-Sessions (separate / merge / hide) for Cursor cursor / cursor-cli hooks whose transcript_path is under …/agent-transcripts/<parentId>/… while session_id is a child. Merge rewrites to the parent + agent_id; hide drops the child; separate (default) keeps a separate card — no forced merge.
• Lifecycle: After Stop, record closed Task ids and drop idle orphan cards so a still-open IDE process cannot revive them. Keep the parent active while merged Tasks are still running. Deny/drop late Permission / Question / AskUserQuestion for closed Tasks. Relaunch on UserPromptSubmit / beforeSubmitPrompt. When splitting to separate, do not tail the parent transcript twice.
• Hardening: Denying or answering a merged Task must not idle the parent card. An idle orphan must not overwrite a live merged Task. Only Task cards (transcript parent ≠ session id) self-close on Stop; parent chats keep cliPid. Persist closedSubagentIds. Settings copy mentions Cursor Task/subagent.
• AppState teardown: Allow AppState deinit off the main actor (async XCTest / ARC). FSEvents callbacks hold a weak-boxed watcher so queued main-queue deliveries stay safe; avoids MainActor.assumeIsolated traps.
• Tests: CursorSessionFoldingTests, AppStateCursorSubsessionTests, SessionPersistenceTests, AppStateDeinitTests.

中文说明

• 路由： Cursor（cursor / cursor-cli）在「子 session_id + transcript 仍指向父对话」时，走同一套 Agent 子会话设置。合并 → 父 session + agent_id；隐藏 → 丢弃；默认独立显示，不强制合并。
• 生命周期： Stop 后写入 closed，并丢掉空闲孤儿卡，避免 IDE 进程仍在时被拉活；父 turn 结束时若仍有合并中的 Task，父卡保持活跃；closed 后的晚到 Permission/Question/AskUserQuestion 直接拒绝或丢弃；新 prompt 可重新打开；拆成独立卡时不重复 tail 父 transcript。
• 加固： 合并态 deny/回答不得把父卡打成 idle；空闲孤儿卡不得覆盖正在跑的合并 Task；仅 Task 卡（transcript 父 id ≠ 本卡 id）在 Stop 时自记录 closed，父会话保留 cliPid；持久化 closedSubagentIds；设置文案补充 Cursor Task/subagent。
• AppState 销毁： 允许非主线程 deinit（异步 XCTest / ARC）。FSEvents 经弱引用 box 回调，避免 MainActor.assumeIsolated 崩溃。
• 测试： 同上，另含 AppStateDeinitTests。

Test Plan

• DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer — CursorSessionFoldingTests (24), AppStateCursorSubsessionTests (26), SessionPersistenceTests (6), AppStateDeinitTests (1) — all passed
• Settings → Behavior → Agent Sub-Sessions: copy mentions Cursor; default Show separately / 独立显示 (verified: L10n + SettingsDefaults.pluginSessionMode == "separate")
• Manual separate: Cursor Task → separate card; Stop is not revived while IDE stays open (unit coverage: separate leave/split + Stop self-tombstone + no IDE-ppid revive)
• Manual merge: Task appears under the parent; parent stays active if Task still runs after parent AfterAgentResponse / Stop (unit coverage: fold + parent keeps active)
• Manual hide: Task does not appear as a card (unit coverage: hide removes/clears cards)
• Manual: after merged Task Stop, late Permission / Question / AskUserQuestion are denied/dropped; a new prompt relaunches cleanly (unit coverage: closed-agent deny/drop + UserPromptSubmit reopen)
• Manual: deny a merged Task Permission — parent stays .running with tool Agent, not .idle (unit coverage: testMergedPermissionMarksSubagentWaitingApproval)
• Confirm async XCTest suites that construct AppState no longer SIGTRAP on teardown (AppStateDeinitTests passed)