pipeio_completion — per-session completion tracking

Goal

(promoted from note)

Context

(see source note)

Prompt

Implement pipeio_completion(pipe, flow, mod=None) — check which sessions are complete/partial/missing/stale by comparing expected outputs (from registry + pybids_inputs) against filesystem.

Reference capture: 20260325-211434-233304.

Acceptance Criteria

• [ ]

Result

(pending)