# Task: Pipeline orchestrator API endpoints

## Goal
Create the API endpoints for triggering and monitoring pipeline runs. This is Phase 2 — the API layer on top of the task definitions from the previous task.

## Requirements

### Create `src/backend/services/pipeline_orchestrator.py`

Implement `PipelineOrchestrator` class:

1. `run_pipeline(task_name: str, user_id: str) -> str` — start a pipeline run, return run_id
2. `get_run_status(run_id: str) -> dict` — return run status (pending/running/completed/failed)
3. `cancel_run(run_id: str)` — cancel a running pipeline
4. Internal: execute tasks respecting dependency order
5. Store run state in memory (dict) — no DB needed yet

### Create `src/backend/routers/pipeline.py`

Add endpoints:

1. `POST /api/v1/pipeline/run` — trigger a pipeline run
   - Body: `{"task": "news_ingestion"}` or `"full"` for all tasks
   - Returns: `{"run_id": "...", "status": "pending"}`

2. `GET /api/v1/pipeline/run/{run_id}` — get run status
   - Returns: `{"run_id": "...", "status": "...", "tasks": [...]}`

3. `POST /api/v1/pipeline/run/{run_id}/cancel` — cancel a run
   - Returns: `{"message": "cancelled"}`

4. `GET /api/v1/pipeline/tasks` — list available tasks
   - Returns: list of registered tasks with descriptions

### Response models in `schemas/pipeline.py`

Create:
- `PipelineRunRequest` — task name to run
- `PipelineRunResponse` — run_id and status
- `PipelineRunStatus` — detailed run status with task results
- `PipelineTaskInfo` — task metadata

## Acceptance Criteria
1. All 4 endpoints work correctly
2. Dependency order is respected when running full pipeline
3. Run status updates in real-time
4. Files stay under 200 lines each

## Files to Create/Modify
- `src/backend/services/pipeline_orchestrator.py`
- `src/backend/services/pipeline_tasks.py` (from previous task)
- `src/backend/routers/pipeline.py`
- `src/backend/schemas/pipeline.py`

## Files to Read First
- `src/backend/services/pipeline_tasks.py` — task definitions
- `src/backend/routers/alerts.py` — follow routing pattern
- `src/backend/schemas/alert.py` — follow schema pattern