why

Overview ¶

Package why implements the causal-explainer endpoint (data-plane-memory A3):

GET /v1/jobs/:id/runs/:run_id/why?task=<task-name-or-id>[&partition=<value>]

It returns a field-by-field explanation of why the given task in the run executed, hit the cache, or re-ran — diffing the persisted HashInput blobs and joining trigger-side causation from the event store.

Fan-out: a fanned step has N task_runs rows for one (run, task), so `?task=` alone cannot name an instance. Without `partition` the response is the GROUP summary (partition count, status histogram, first failure, aggregate timing); with `partition=<value>` it is that one instance's full explanation. An unknown partition value is a 404 whose message lists the available values.