Make _EcsSubscriber cloudpickle-safe so ECS workflow dispatch survives the wool reduce boundary — Closes #60

[conradbzura]

Summary

ECS-profile workflow dispatch failed before any preprocessing ran: a GET /data|/index for an uncached processable file returned 202, then the job terminated failed with cannot pickle '_asyncio.Future' object. wool's WorkerProxy.__wool_reduce__ serializes the dispatched task's discovery, which in the no-spawn WorkerPool branch is cfdb's _EcsSubscriber (the EcsDiscovery rides along as its _owner). While the API's WorkerPool consumes the subscriber, its asyncio.Queue holds a pending-getter _asyncio.Future that cloudpickle cannot serialize. _EcsSubscriber defined no pickle protocol, so #54's EcsDiscovery fix did not reach it.

Make _EcsSubscriber honor wool's documented picklability contract by adding __getstate__/__setstate__ mirroring EcsDiscovery one level deeper: strip the live queue and the single-use flag on pickle, recreate a fresh inert queue on unpickle. The worker never consumes the restored subscriber, so an empty queue is correct. This is the targeted unblock; a follow-up (#61) replaces the per-object hand-stripping with an inert worker-side discovery stub.

Closes #60

Proposed changes

Add the pickle protocol to _EcsSubscriber (src/cfdb/workflows/discovery.py)

• __getstate__ copies __dict__ and drops _queue (its internal getter deque holds the unpicklable pending _asyncio.Future mid-consumption, and the queue is bound to the API event loop) plus the single-use _exhausted flag. _owner (already pickle-safe via EcsDiscovery.__getstate__) and _filter carry across.
• __setstate__ restores the dict, then mints a fresh asyncio.Queue() and resets _exhausted = False, yielding a well-formed, inert subscriber.

Add a regression test for the consumed-subscriber path (tests/test_workflows/test_discovery.py)

• Add test_subscriber_roundtrip_should_succeed_when_queue_has_pending_getter to TestEcsDiscoveryPickleAgainstMoto. It drives the subscriber into the live being-consumed shape — a getter parked on the queue plus the flipped flag — over a real moto-backed boto3 client, the state the existing fresh-subscriber round-trip never reproduced (it passed while production failed). It asserts cloudpickle.dumps succeeds and the restored subscriber is inert: empty queue, reset flag, retained filter, rebuilt owner client.

Test cases

#	Test Suite	Given	When	Then	Coverage Target
1	TestEcsDiscoveryPickleAgainstMoto	An _EcsSubscriber over a real moto-backed client with a getter parked on its queue and the single-use flag set	The subscriber is cloudpickle dumped and loaded back	It serializes successfully and restores an inert handle with an empty queue, a reset flag, a retained filter, and a rebuilt owner client	_EcsSubscriber.__getstate__ / __setstate__