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/childProcess.ts

@@ -0,0 +1,78 @@
+import { ChildProcessWithoutNullStreams } from 'child_process';
+import { Readable } from 'stream';
+
+export interface ProcessResult {
+  code: number | null;
+  signal: NodeJS.Signals | null;
+  error?: Error;
+}
+
+export function asError(error: unknown): Error {
+  return error instanceof Error ? error : new Error(String(error));
+}
+
+/** Attach immediately after spawn, before awaiting database or user callbacks. */
+export function observeChildProcess(
+  child: ChildProcessWithoutNullStreams,
+  callbacks: {
+    onStart?: () => Promise<void>;
+    onStdout?: (message: string) => Promise<void>;
+    onStderr?: (message: string) => Promise<void>;
+  } = {},
+) {
+  let failure: Error | undefined;
+  const recordError = (error: unknown) => {
+    failure ??= asError(error);
+  };
+  const spawned = new Promise<void>((resolve, reject) => {
+    child.once('spawn', resolve);
+    // Keep the listener through close: errors can occur after a successful spawn.
+    child.on('error', (error) => {
+      recordError(error);
+      reject(error);
+    });
+  });
+  const closed = new Promise<ProcessResult>((resolve) => {
+    child.once('close', (code, signal) => resolve({ code, signal }));
+  });
+  const started = spawned.then(async () => {
+    await callbacks.onStart?.();
+    return child.pid;
+  });
+  // The caller can ask only for completion, without an unhandled start rejection.
+  const ready = started.catch(recordError);
+
+  const consume = async (
+    stream: Readable,
+    callback?: (message: string) => Promise<void>,
+  ) => {
+    // StringDecoder in Readable preserves UTF-8 characters split across chunks.
+    stream.setEncoding('utf8');
+    let callbackFailed = false;
+    try {
+      for await (const chunk of stream) {
+        await ready;
+        if (!callbackFailed && callback) {
+          try {
+            await callback(String(chunk));
+          } catch (error) {
+            recordError(error);
+            callbackFailed = true;
+          }
+        }
+        // Even if a log sink fails, drain the pipe so the child can finish.
+      }
+    } catch (error) {
+      recordError(error);
+    }
+  };
+  const output = Promise.all([
+    consume(child.stdout, callbacks.onStdout),
+    consume(child.stderr, callbacks.onStderr),
+  ]);
+  const completed = Promise.all([closed, ready, output]).then(([result]) => ({
+    ...result,
+    error: failure,
+  }));
+  return { started, completed };
+}