fix(train): plan policy updates outside the policy-root tree lock

[akushonkamen]

Description

本 PR 修复训练引擎在策略根目录整树锁内执行远程 LLM 规划导致的并发阻塞（#6095）。

根因：openviking/session/train/engine.py 的 plan_and_apply 在 policy_set.lock() 整根树锁内依次执行 reload → policy_optimizer.plan（远程 LLM 调用，生产 trace 中为分钟级）→ apply。并发 session-commit 在 openviking/session/train/domain.py 的 pathlock_acquire_tree(timeout_secs=300.0)（原先硬编码）上等待，等满 300s 后终态失败。（实测基于 HEAD=6006fc34：锁调用在 domain.py:84，docstring 中 "timeout=None means wait indefinitely" 的承诺在 :72，实现从未支持 None；工单引用 :100 为行漂移。）

修法：把规划移到锁外——先无锁 reload 出快照并基于快照规划；拿锁后仅做 reload 校验快照仍然一致才 apply；不一致则基于新快照有界重规划（_PLAN_APPLY_MAX_REPLANS=2）；重规划预算耗尽后，带 optimistic_apply_after_conflict 标记对最新快照守卫应用，由 updater 既有 per-item before_content 基线守卫把过期目标转为记录错误而非静默覆盖。同时 PolicySet.lock 增加 timeout_secs 参数（默认 300s 不变），并修正 docstring 与实现不符的 "None=无限等待" 承诺。

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Fixes #6095

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• engine.py：plan_and_apply 改为"锁外快照规划 + 锁内校验后短临界区应用"；快照冲突时基于新快照有界重规划（上限 _PLAN_APPLY_MAX_REPLANS=2）；预算耗尽后带 optimistic_apply_after_conflict 标记守卫应用，过期目标由既有 per-item 基线守卫报错而非静默覆盖。
• domain.py：PolicySet.lock 新增 timeout_secs 关键字参数（默认 300.0，行为不变），锁调用透传该参数；docstring 删除实现从未支持的 "timeout=None 无限等待" 承诺，改为说明临界区应保持短小、远程 LLM 规划须在锁外执行。
• tests/session/train/test_fakes.py：新增 LockingAGFS（具备真实互斥、deadline 处理与持锁区间记录的树锁 fake）；DummyVikingFS 补上 lock() 所需的 _async_agfs 属性。
• tests/session/train/test_train_framework.py：新增 5 条锁回归测试——(1) 2s 规划不再在 1s 锁预算内阻塞并发写者；(2) 快照冲突触发有界重规划并对最新快照守卫应用；(3) 无竞争快路径仅规划一次并释放锁；(4) 锁超时参数透传、出错时释放租约。

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

本地验证（红→绿）：

• 新增 5 条锁回归测试在修复前代码上 3 failed（并发阻塞 / 有界重规划 / 超时参数；均 1.5s 内快速失败）→ 修复后 5 passed。
• OPENVIKING_CONFIG_FILE=/tmp/ovtest/ov.conf timeout 300 uv run --no-sync pytest tests/session/train/test_train_framework.py -q --override-ini addopts=""：修复后 39 passed（基线 14 failed / 20 passed；14 条为 main 上既有的 DummyVikingFS 缺 _async_agfs 红，被本修复转绿）。
• OPENVIKING_CONFIG_FILE=/tmp/ovtest/ov.conf timeout 300 uv run --no-sync pytest tests/session/train/ -q --override-ini addopts=""：103 passed / 12 failed；12 条已用 git stash 在干净 HEAD 复跑证实为同集既有环境性失败（2 real-LLM e2e + 10 tau2），与本修复无关。
• 受害方（并发提交方）回归：uv run --no-sync pytest tests/session/memory/test_streaming_memory_updater.py tests/session/train/test_train_components.py -q：72 passed / 0 failed。
• uv run --no-sync ruff check openviking/session/train/engine.py openviking/session/train/domain.py tests/session/train/test_fakes.py tests/session/train/test_train_framework.py：All checks passed。
• 基线具名筛选命令 OPENVIKING_CONFIG_FILE=/tmp/ovtest/ov.conf timeout 300 uv run --no-sync pytest tests/session/train/test_train_framework.py -q -k 'plan or lock' --override-ini addopts=""：修复前 0 selected / 34 deselected（既有测试名无匹配，如实记录）；修复后同命令 5 passed。

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

• 补丁由 AI 辅助准备并经人工评审（Human Involvement 如上勾选）。
• 本地环境 ~/.gitconfig 存在 http.proxy https.proxy 误配，HTTPS git 操作需按次 -c http.proxy= 覆盖，与 upstream 无关。

[akushonkamen]

Thanks for the runs! About the one failing check — API & CLI Integration Tests (ubuntu-24.04) ends with 5 failed, 8 passed, 1 skipped, and all five failures are the same server-side error, e.g.:

PROCESSING_ERROR: Failed to generate embedding: Volcengine embedding failed: Error code: 401 - {'error': {'code': 'AuthenticationError', 'message': 'The API key format is incorrect. ...'}}

So the integration environment's Volcengine embedding credentials are being rejected (401 Unauthorized). This PR doesn't touch the embedding/API surface at all — the diff is limited to openviking/session/train/domain.py, openviking/session/train/engine.py and the train tests. The same workflow fails identically on unrelated PRs: run 38811885113 (fix/6130-orphan-running-task-expiry) shows the same 5 failed, 8 passed, 1 skipped with the same 401 signature, so this looks like a CI-side credential issue rather than anything introduced here.

For what it's worth, the checks that do run on this PR are green (check-deps, plugin-tests, plugin-versions; the others skip by path filter), and the unit tests covering this change pass locally on this branch (b6fb190):

uv run python -m pytest tests/session/train/test_fakes.py tests/session/train/test_train_framework.py
→ 39 passed, 0 failed

Happy to help debug the CI credentials if useful — thank you!