# TASK 5.1: Implement Load-To-Staging Orchestration And Upstream Normalize-Load Batch Resolution

## Summary

Implement the tenant-day `load_to_staging` entry point and the ETL/Warehouse orchestration flow that starts one `load -> Redshift staging` run for Brink `Sales2.GetOrders` contracts.

This subtask turns the replay boundary from `TASK4.md` and the lifecycle contract from `TASK3.md` into a concrete execution path that resolves the upstream normalize-load batch, reads the produced load inventory, and prepares Redshift staging execution.

## Dependencies

- [TASK 3](./TASK3.md) - batch lifecycle, checkpoints, and failure packaging
- [TASK 4](./TASK4.md) - raw to load normalization

## Files to Create

### 1. Load-to-staging orchestration services

Create or finalize the services responsible for one tenant-day `load_to_staging` execution.

Recommended logical services:

- `BrinkPosLoadToStagingJobs`
- `BrinkPosNormalizeLoadBatchResolver`
- `BrinkPosStagingLoadOrchestrator`

## Required Behavior

- child load-to-staging accepts a `BrinkPosLoadToStagingJobInput`-style contract
- explicit `NormalizeLoadBatchId` wins when provided
- otherwise the resolver loads the current successful `normalize_load` batch for the same tenant-day key
- the upstream normalize-load batch must be successful and replayable
- orchestration resolves the produced `load/` artifact inventory from persisted batch metadata rather than from in-memory normalization state
- the orchestration layer passes only upstream batch context and contract inventory into the staging-load boundary

## Testing

### Unit tests

Add unit tests for:

- explicit upstream normalize-load batch selection
- implicit upstream normalize-load batch selection through current-state lookup
- rejection of failed or invalid upstream normalize-load batches
- load-inventory resolution from persisted batch metadata
- orchestration handoff from child job to staging-load execution

## Acceptance Criteria

- [x] Child load-to-staging job entry exists
- [x] Upstream normalize-load batch resolution exists for explicit and implicit selection paths
- [x] Failed or invalid upstream normalize-load batches are rejected
- [x] Produced load inventory is resolved from persisted batch metadata
- [x] Unit tests cover upstream resolution and orchestration behavior

## Notes

- Keep this subtask focused on stage orchestration readiness.
- Do not implement contract-to-table mapping or Redshift execution here; those belong to later subtasks in `TASK 5`.