fix: 修复任务生命周期与调度就绪，优化执行和构建开销 (#3069)

* fix: harden task lifecycle and scheduler readiness

* fix: confine log writes to the configured log directory

* fix: verify complete build artifacts and untracked inputs

* fix: reconcile scheduler state and make stop win startup races

* fix: isolate cron generations and serialize scheduler recovery

back/shared/schedulerReadiness.ts

@@ -0,0 +1,77 @@
+// Recovery is single-flight and retried only while unavailable, never at idle.
+export class SchedulerReadiness {
+  private ready = false;
+  private generation = 0;
+  private restore?: () => Promise<void>;
+  private pending?: Promise<boolean>;
+  private retry?: NodeJS.Timeout;
+
+  constructor(private probe: () => Promise<void>, private retryMs = 1000) {}
+
+  configure(restore: () => Promise<void>) {
+    this.restore = restore;
+  }
+
+  invalidate() {
+    this.ready = false;
+    this.generation++;
+    void this.recover();
+  }
+
+  recover(): Promise<boolean> {
+    if (this.pending) return this.pending;
+    if (!this.restore) return Promise.resolve(false);
+    clearTimeout(this.retry);
+    const generation = this.generation;
+    this.ready = false;
+    this.pending = (async () => {
+      try {
+        await this.probe();
+        await this.restore!();
+        await this.probe();
+        this.ready = generation === this.generation;
+      } catch {
+        this.ready = false;
+      }
+      return this.ready;
+    })().finally(() => {
+      this.pending = undefined;
+      if (!this.ready) {
+        this.retry = setTimeout(() => void this.recover(), this.retryMs);
+        this.retry.unref();
+      }
+    });
+    return this.pending;
+  }
+
+  async check(): Promise<boolean> {
+    if (!this.ready) return false;
+    const generation = this.generation;
+    try {
+      await this.probe();
+      return this.ready && generation === this.generation;
+    } catch {
+      this.invalidate();
+      return false;
+    }
+  }
+
+  async ensureReady(timeoutMs = 2000): Promise<void> {
+    let timer: NodeJS.Timeout | undefined;
+    try {
+      const available = await Promise.race([
+        (async () => (await this.check()) || (await this.recover()))(),
+        new Promise<boolean>((resolve) => {
+          timer = setTimeout(() => resolve(false), timeoutMs);
+        }),
+      ]);
+      if (!available) {
+        throw Object.assign(new Error('Scheduler is recovering; try again later'), {
+          status: 503,
+        });
+      }
+    } finally {
+      clearTimeout(timer);
+    }
+  }
+}