V1 order request models miss ge=0 on subaccount/exchange_index that V2 and other models enforce #326

Problem

Every V2 request model, the communications/order_groups request models, and the subaccount-transfer body enforce ge=0 on subaccount-shaped integer fields. The V1 order family — CreateOrderRequest, AmendOrderRequest, DecreaseOrderRequest, BatchCancelOrdersRequestOrder — uses bare StrictInt | None with no lower-bound constraint. A caller passing subaccount=-1 or exchange_index=-7 to V1 constructs cleanly, the SDK signs the request, and the server rejects with 400.

This undermines the invariant the docstring on ApplySubaccountTransferRequest calls out — that subaccount fields validate the lower bound so server-assigned numbers always round-trip. v2.6's #295 already retro-fitted StrictInt to these same fields, so they were touched once; adding ge=0 is the same one-line shape.

Evidence

• kalshi/models/orders.py:194-195 (V1 CreateOrderRequest — bare StrictInt | None):

subaccount: StrictInt | None = None
exchange_index: StrictInt | None = None

• kalshi/models/orders.py:269-270, 291-292, 335-336 — same pattern in AmendOrderRequest, DecreaseOrderRequest, BatchCancelOrdersRequestOrder.
• kalshi/models/orders.py:482 (V2 CreateOrderV2Request enforces it):

subaccount: StrictInt | None = Field(default=None, ge=0)

• kalshi/models/orders.py:625 (BatchCancelOrdersV2RequestOrder), kalshi/models/communications.py:160, kalshi/models/order_groups.py:59, kalshi/models/subaccounts.py:34 — all use Field(..., ge=0).
• Note: CreateOrderV2Request.exchange_index at kalshi/models/orders.py:484 and BatchCancelOrdersV2RequestOrder.exchange_index at :626 are also bare StrictInt | None, so the parity fix should sweep those too.

Suggested fix

Replace bare declarations with Field(default=None, ge=0) on every subaccount-shaped int across the V1 order models and the two V2 exchange_index slots that were missed:

• CreateOrderRequest.subaccount, CreateOrderRequest.exchange_index
• AmendOrderRequest.subaccount, AmendOrderRequest.exchange_index
• DecreaseOrderRequest.subaccount, DecreaseOrderRequest.exchange_index
• BatchCancelOrdersRequestOrder.subaccount, BatchCancelOrdersRequestOrder.exchange_index
• CreateOrderV2Request.exchange_index
• BatchCancelOrdersV2RequestOrder.exchange_index

Extend tests/test_models.py's negative-value coverage (which today only exercises V2 + communications) to these classes.

Source

Round-3 independent audit (reviewer: models_contracts).