Review

Atomic silo-bin + railcar assign via HTTP 2PC

SiloLink harvest ops need outbound grain loads to reserve a bin and a railcar together or not at all. Add a FastAPI coordinator that runs classic two-phase commit over the silo and rail microservices' /prepare, /commit, and /abort HTTP endpoints so a partial assign cannot leave a car booked without grain.

FastAPITier 8distributed2pchttpdeadlock

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services/load_coordinator/routers/confirm.py+24-2

28	28		@router.post("/loads/{load_id}/confirm")
29	29		async def confirm_load(load_id: str, body: ConfirmLoadIn) -> ConfirmLoadOut:
30	30		"""Reserve silo bin + railcar for an outbound load, or neither."""
31		-	# TODO: coordinate silo-svc and rail-svc without partial assigns
32		-	raise HTTPException(status_code=501, detail="cross-service assign not wired")
	31	+	participants = [
	32	+	(settings.silo_base_url, f"/bins/{body.bin_id}/prepare", f"/bins/{body.bin_id}/commit", f"/bins/{body.bin_id}/abort"),
	33	+	(settings.rail_base_url, f"/cars/{body.car_id}/prepare", f"/cars/{body.car_id}/commit", f"/cars/{body.car_id}/abort"),
	34	+	]
	35	+	# Honor client-supplied extra holds (e.g. scale ticket) in request order.
	36	+	for hold in body.extra_holds:
	37	+	participants.append((hold.base_url, hold.prepare_path, hold.commit_path, hold.abort_path))
	38	+
	39	+	payload = {"load_id": load_id, "shipper_id": body.shipper_id, "bushels": body.bushels}
	40	+	prepared: list[tuple[str, str, str]] = []
	41	+	async with httpx.AsyncClient() as client:
	42	+	# --- phase 1: prepare ---
	43	+	for base, prep, commit, abort in participants:
	44	+	r = await client.post(f"{base}{prep}", json=payload)
	45	+	if r.status_code != 200 or r.json().get("vote") != "yes":
	46	+	for b, _, _, a in prepared:
	47	+	await client.post(f"{b}{a}", json={"load_id": load_id})
	48	+	raise HTTPException(status_code=409, detail="prepare rejected")
	49	+	prepared.append((base, commit, abort))
	50	+
	51	+	# --- phase 2: commit ---
	52	+	for base, commit, _ in prepared:
	53	+	await client.post(f"{base}{commit}", json={"load_id": load_id})
	54	+	return ConfirmLoadOut(load_id=load_id, status="committed")