Pipeline task management

Session persists a collection of tasks with unique identifiers; shared pipeline caller can optionally enqueue its call as a task instead of running it directly

model_server/base/api.py

@@ -6,7 +6,7 @@ from .accessors import generate_file_accessor
 from .models import BinaryThresholdSegmentationModel
 from .pipelines.shared import PipelineRecord
 from .roiset import IntensityThresholdInstanceMaskSegmentationModel, RoiSetExportParams, SerializeRoiSetError
-from .session import session, AccessorIdError, InvalidPathError, RoiSetIdError, WriteAccessorError
+from .session import session, AccessorIdError, InvalidPathError, RoiSetIdError, RunTaskError, WriteAccessorError
 
 app = FastAPI(debug=True)
 
@@ -220,7 +220,10 @@ class TaskInfo(BaseModel):
 
 @app.put('/tasks/{task_id}/run')
 def run_task(task_id: str) -> PipelineRecord:
-    return session.queue.run_task(task_id)
+    try:
+        return session.queue.run_task(task_id)
+    except RunTaskError as e:
+        raise HTTPException(409, str(e))
 
 @app.get('/tasks/{task_id}')
 def get_task(task_id: str) -> TaskInfo: