feat(tasks): OpenWorkflow-backed TaskEngine, task registry, outbox relay and op-ledger fencing (W1-4)

- TaskEngine port + OpenWorkflowEngine ([email protected].1, schema openworkflow):
  enqueue/signal/cancel/get/list/startWorker/stop
- defineTask registry with zod input schema; 9 stub task definitions (§3.1-8)
- TaskContext: step.run/sleep/waitForFact, redacting logger, traceId,
  attemptToken, abortSignal driven by PG cancel flag
- signal persists fact to tasks_fact first; waitForFact checks DB before waiting
- OutboxRelay: FOR UPDATE SKIP LOCKED, idempotencyKey outbox:<id>
- withAttemptToken fencing on tasks_op_ledger (own migration, merged in W2)
- tests: kill -9 crash recovery (child worker), cancel, idempotency,
  concurrent relays, early fact, lease-loss fencing

Co-Authored-By: Claude Fable 5.1 <[email protected]>

packages/tasks/src/index.ts

@@ -1,2 +1,47 @@
-// @umt/tasks 公开入口;W1 起在此导出实现
+// @umt/tasks 公开入口:TaskEngine 端口 + OpenWorkflow 实现、任务注册表、outbox 中继、操作账本 fencing
 export const PACKAGE_NAME = "@umt/tasks";
+
+export {
+  cleanupDownloadCache,
+  createDefaultRegistry,
+  evaluateAcquisition,
+  ingestFeed,
+  reconcileLibrary,
+  refreshMetadata,
+  resolveDecision,
+  resolveObservation,
+  submitDownload,
+  TASK_NAMES,
+  type TaskName,
+  verifyAndImport,
+} from "./definitions";
+export { FencingError, TaskCanceledError, UnknownTaskError } from "./errors";
+export {
+  consoleSink,
+  createLogger,
+  type LogLevel,
+  type LogRecord,
+  type LogSink,
+  redact,
+  silentSink,
+  type TaskLogger,
+} from "./logger";
+export { migrateTasksTables, TASKS_MIGRATIONS_DIR } from "./migrate";
+export {
+  type AttemptInfo,
+  assertAttemptToken,
+  getOperation,
+  type OpLedgerRow,
+  type WithAttemptTokenOptions,
+  withAttemptToken,
+} from "./op-ledger";
+export { ENGINE_SCHEMA, OpenWorkflowEngine, type OpenWorkflowEngineOptions, signalName } from "./openworkflow-engine";
+export {
+  type OutboxEvent,
+  OutboxRelay,
+  type OutboxRelayOptions,
+  type OutboxRoute,
+  type OutboxRouteFn,
+} from "./outbox-relay";
+export { defineTask, type TaskDefinition, TaskRegistry } from "./registry";
+export type * from "./types";