[Wittig18]

Closes #1297
Closes #1298

Both issues change the same worker boot block in src/index.ts, so they're fixed together: #1298 extracts it, and #1297 adds the scheduler to the extracted version.

#1298: services started twice / in the wrong role

• Removed the unconditional PayoutDriftDetector that started before the role checks and was never stopped.
• New src/services/backgroundServices.ts: startBackgroundServices(roleConfig, factories) starts each batch service (audit purge, session compaction, payout drift, reconciliation, distribution scheduler) at most once, only under its own role flag, and returns a stop function for each. index.ts passes real factories, and tests pass spies.
• Session compaction has its own sessionCompaction flag instead of reusing auditPurge. It's on for batch/all and off for api, so behaviour is the same as before.

#1297: DistributionScheduler never started

• New distributionScheduler role flag: on for batch/all, off for api.
• createDistributionSchedulerRuntime({ engine, revenueReportRepo, scheduledDistributionRepo, intervalMs, metrics }) in distributionScheduler.ts:
  • runs catchUpMissedWindows once at boot, then processPendingDistributions + processScheduledDistributions each tick
  • ticks are chained with setTimeout (the next is scheduled only after the previous finishes), so they never overlap
  • stop() cancels the pending timer and resolves after the in-flight tick finishes
  • interval comes from the option, else DISTRIBUTION_SCHEDULER_INTERVAL_MS, else 60 s
• shutdown() now awaits the background stop functions before closePool(), so an in-flight tick isn't cut off.
• Batch workers never run createApp, so the snapshot-backed balance provider is now a small exported createSnapshotBalanceProvider(). createApp and the worker build the same DistributionEngine.

Extra fix: index.ts used StellarTransactionVerifierImpl without importing it (tsc TS2304 on master), which would throw when batch/all starts the reconciliation scheduler. Added the import.

Tests

• src/__tests__/backgroundServices.test.ts (new):
  • api starts zero services
  • batch and all start each exactly once, including exactly one drift detector
  • every started service has a stop function, for all roles
  • async stops are awaited
  • session compaction is gated on its own flag
  • a regression check on index.ts that the drift detector is only created through startBackgroundServices. On master there are two.
• distributionScheduler.test.ts runtime block, with fake timers:
  • catch-up only once at boot
  • a due scheduled row is executed within one interval
  • a slow tick delays the next one (max concurrency 1)
  • stop() cancels the timer
  • stop() awaits the in-flight tick
  • a throwing tick doesn't stop the loop
• workerRole.test.ts: the new flags across the role matrix.

Results:

• backgroundServices + workerRole: 34/34 pass.
• The runtime block: 6/6 pass.
• The distributionScheduler.test.ts file has 10 holiday-calendar tests that already fail on master. Those are unchanged.
• tsc --noEmit reports no new errors; the TS2304 above is gone. ESLint is clean on the new files.

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