PR1: backfill v3.18.0 fields on Market / Order / Fill

[TexasCoding]

Context

OpenAPI v3.18.0 added fields to Market, Order, and Fill that the SDK does not yet model. Currently TestSpecDrift::test_additive_drift emits UserWarning for each one; these warnings do not fail CI. This is the largest backfill in the stack — 23 fields across the three highest-traffic response models — and lands the new direction-encoding fields (outcome_side / book_side) that supersede the deprecated Order.action.

Depends on #158 (EXCLUSIONS infrastructure). Once #158 lands the warning floor drops; this PR removes 23 of the remaining warnings.

Scope

Files

• kalshi/models/markets.py — add 11 fields to Market
• kalshi/models/orders.py — add 8 fields to Order, 4 fields to Fill
• tests/test_orders.py — extend existing happy-path tests to cover the new fields' (de)serialization
• tests/test_models_markets.py (or wherever Market is exercised — confirm at edit time)

Field-level changes

Market (+11):

Field	Spec type	SDK type	Notes
custom_strike	object	dict[str, Any] | None = None	per-market custom strike spec
early_close_condition	string	str | None = None	enum on the wire; keep str until #PR? for Literal
exchange_index	integer	int | None = None	matches request-side already on CreateOrderRequest
fee_waiver_expiration_time	string (date-time)	datetime | None = None
functional_strike	string	str | None = None
is_provisional	boolean	bool | None = None
mve_collection_ticker	string	str | None = None	multivariate event collection linkage
mve_selected_legs	array	list[str] | None = None	verify element type at edit time
price_level_structure	string	str | None = None	replaces deprecated response_price_units
price_ranges	array	list[dict[str, Any]] | None = None	confirm element schema
primary_participant_key	string	str | None = None

Order (+8):

Field	Spec type	SDK type	Notes
book_side	string	BookSideLiteral | None = None	Literal["bid", "ask"] — already defined in orders.py
cancel_order_on_pause	boolean	bool | None = None
exchange_index	integer	int | None = None
last_update_time	string (date-time)	datetime | None = None
order_group_id	string	str | None = None
outcome_side	string	SideLiteral | None = None	Literal["yes", "no"] — replaces Order.action (already deprecated; stays as str | None)
self_trade_prevention_type	string	SelfTradePreventionTypeLiteral | None = None	already defined
subaccount_number	integer	int | None = None	distinct from existing subaccount field — verify shape

Fill (+4):

Field	Spec type	SDK type	Notes
book_side	string	BookSideLiteral | None = None
outcome_side	string	SideLiteral | None = None
subaccount_number	integer	int | None = None
ts	integer	int | None = None	Unix ms timestamp — distinct from existing created_time: datetime; do NOT auto-convert

Conventions to follow

• model_config = {"extra": "allow", "populate_by_name": True} (existing pattern).
• For fields with spec _dollars / _fp suffix wire names: use Field(default=None, validation_alias=AliasChoices("<wire>_dollars", "<short>")) — see existing examples in the same file.
• For enum-like string fields: type as the existing *Literal alias when one exists; otherwise plain str | None. Don't invent new Literal aliases in this PR — that's separable polish.
• Don't reorder existing fields. Append new ones at the end of each model (matches the spec's append-only evolution).
• Do not touch the model docstrings except to add a one-line note about new fields where it improves clarity.

Acceptance criteria

• uv run pytest tests/test_contracts.py::TestSpecDrift::test_additive_drift -v shows no warnings for Market, Order, Fill (the three parameterized cases pass cleanly).
• Other test_additive_drift cases still warn for the remaining un-backfilled models (these are addressed in #PR2–#PR4).
• uv run pytest tests/test_orders.py -v passes; new (de)serialization tests cover at least one field per backfilled model.
• uv run pytest tests/ -q --ignore=tests/integration passes (1945 → 1945+N).
• uv run mypy kalshi/ strict-clean.
• uv run ruff check . clean.
• No changes to request-body models or resource methods.

Notes

• Order.outcome_side and Order.book_side are the canonical direction encodings going forward. Order.action stays in the model (allowlisted in PR0: test infra — wire response-side drift through EXCLUSIONS map #158) for back-compat — the spec still emits it.
• subaccount_number is not the same as the existing Order.subaccount: int | None. Verify against specs/openapi.yaml Order schema at edit time; the spec adds it as a separate property.

Effort

~80 lines model code + ~30 lines tests.

Part of the response-side spec drift hardening stack.

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Tracking: #157.