feat(scheduler): restore PEND-reason P1 + fix dispatchwindow merge regressions

The scheduler-framework merge (2026-08-25) silently regressed the PEND
reason P1 work (4e2ac86/ee79179): the old fcfs.c became dead-on-default
(builtin_fcfs replaced it), resource.c/limit.c conflict resolution took
Rongsong's side, and the merge-fix only re-added the dispatchwindow FIELD
without the logic. After the merge, sched_queue_is_ready/sched_job_is_ready
were `return 1` stubs and only MATCH_FAIL/NO_RESOURCE were ever emitted.

Restore P1 on the active (framework) path, keeping every reason attach in
the allocator thread (bug-1521: the picker thread must not write
job->schedobj->reason — it races the allocator's MOVE_PTR):

- core.c: sched_job_is_ready (PEND & not suspended) and sched_queue_is_ready
  (QUEUE_STAT_CLOSED/INACT_ADMIN/INACT_WINDOW gate) real implementations.
- scheduler.c: allocator loop injects sched_queue_status_reason() — queue
  status first, then the dispatch window evaluated against the core's
  virtual clock (xce_core_now/1e9) so live and sim modes agree; attaches
  QUEUE_CLOSED/DRAINING/TIME_WINDOW and pends the job. Adds <time.h>.
- resource.c: skip UNAVAIL/CLOSED/CLOSED_BY_ADMIN workers + HOST_UNAVAIL
  (restored from 4e2ac86).
- limit.c: attach LIMIT_GLOBAL/LIMIT_HOST + carry reason in
  limit_job_election (restored from 4e2ac86).

Two further merge regressions found during cluster verification (the
framework core path never carried the queue dispatch window):

- core_events.c core_build_queue: duplicate q->dispatchwindow_config onto
  xce_sched_queue_t.dispatchwindow (make_sched_queue did this; the core path
  dropped it, so TIME_WINDOW could never fire on the default path).
- core_events.c core_upsert_queue update branch: refresh dispatchwindow on
  QUEUE_UPDATE.

Regression test: test_core_ready_gates.c (white-box #include of core.c,
7 cases covering both gates), registered in scheduler testsuite meson.build.

Cluster-verified on t1/t2/t3 (nix xcecore closure + AppImage standard
deployment): night queue (window closed) -> main_reason=8 time_window;
all workers down -> main_reason=9 host_unavail with per-host detail;
closed queue -> job stays PEND; normal queue baseline -> DONE. Scheduler
suite 52/53 (1 pre-existing admin-request symlink-escape failure, unrelated).

Co-Authored-By: Claude Code <noreply@anthropic.com>

docs/left_scheduler_work.md

@@ -204,6 +204,8 @@ spec 声称 36/36 任务完成，但 re-audit（research.md）发现缺陷。来
   - **code 策略已定**：扩展 PREASON_* 枚举到 9 个（BAD_RESREQ/NO_RESOURCE/MATCH_FAIL/LIMIT_GLOBAL/LIMIT_HOST/QUEUE_CLOSED/QUEUE_DRAINING/TIME_WINDOW/HOST_UNAVAIL），capnp UInt32 无限制。
   - **P0**：main_reason 修复（首个 detail code 设为主因，集群验证 PEND 作业 main_reason 非 0 + reason_name）+ limit 插件 attach（host 限额→LIMIT_HOST+limit 名，全局限额→LIMIT_GLOBAL+limit 名）。**集群验证**：PEND 作业 API 显示 `main_reason:3 main_reason_name:"match_fail"` + 每条 host/res reason 带 reason_name。
   - **P1 部分**：队列状态（sched_queue_is_ready 非 stub，closed/inactive 队列不参选 + fcfs election attach QUEUE_CLOSED/DRAINING）；worker 过滤（sched_try_alloc_on_host_ 跳过 UNAVAIL/CLOSED worker + HOST_UNAVAIL）。
+  - **⚠️ scheduler-framework 合并（2026-08-25）回归掉 P1**：P1 改动点（4e2ac86/ee79179）在旧 `fcfs.c`，框架合并用 `builtin_fcfs` 取代后旧 fcfs.c 成死路径；`resource.c`/`limit.c` 冲突取 theirs 直接丢；merge-fix 只补 dispatchwindow **字段**不补逻辑；验证从未跑。合并后 `sched_queue_is_ready`/`sched_job_is_ready` 是 `return 1` stub（core.c），仅 3 处 preason emit。
+  - **✅ P1 已恢复（2026-08-30）**：core.c 恢复 job 状态门 + queue 状态门；scheduler.c allocator 循环注入 `sched_queue_status_reason`（状态→QUEUE_CLOSED/DRAINING，时间窗→TIME_WINDOW，用 `xce_core_now` 虚拟时钟）；resource.c 恢复 worker 过滤+HOST_UNAVAIL；limit.c 恢复 LIMIT_GLOBAL/HOST attach。**全部 reason attach 走 allocator 线程（bug-1521 安全）**。单测通过（新增 `test_core_ready_gates.c`，scheduler 套件 52/53，唯一失败是既有的 admin-request 校验顺序问题与 P1 无关）。遗留：持续 closed 队列的作业被 picker 跳过（spec 契约）到不了 allocator → 收不到 reason（合并前 #17 后同样如此，非新回归）。集群验证待做。
   - **剩余（P2，超出 PEND reason 范畴，属 scheduler 特性开发）**：依赖 depend_cond / license / 保留 RsvID / exclusive / fairshare——机制本身在 scheduler 未实现（设计文档：调度器无处理）；机制落地后 reason 自动出现，MCP 侧无需改。已收尾：TIME_WINDOW 已实现（ee79179，2026-08-15）；`scheduler_pend_reasons` 工具（bjobs -p 等价）已上线（67abbfa，2026-08-15）。
 
 ### 5. 设计层加固（文档已写、代码零实现）