fix(orders): reject bool in CreateOrderRequest.buy_max_cost validator

`buy_max_cost` is integer cents, but bool is an `int` subclass.
`buy_max_cost=True` was slipping through as the integer 1 (= a 1 cent
cap) — the exact failure mode #225 closed for `DollarDecimal` and
`FixedPointCount`. A caller who accidentally passed a flag (e.g.
`risk_check_passed`, `dry_run`) where cents were expected ended up
placing a real order capped at $0.01 with no error.

Prepend an `isinstance(v, bool)` rejection before the Decimal/float
branches, mirroring the wording/style of the existing rejections.
Audited the file: `buy_max_cost` is the only field with a
Decimal/float guard, so no other validators need the same patch.

Closes #243

Author: worker

kalshi/models/orders.py

@@ -198,16 +198,26 @@ class CreateOrderRequest(BaseModel):
 
     @field_validator("buy_max_cost", mode="before")
     @classmethod
-    def _reject_decimal_and_float_buy_max_cost(cls, v: object) -> object:
-        """Reject Decimal and float inputs on buy_max_cost.
+    def _reject_decimal_float_and_bool_buy_max_cost(cls, v: object) -> object:
+        """Reject Decimal, float, and bool inputs on buy_max_cost.
 
         Spec says integer cents. Accepting Decimal would silently coerce
         callers who pass Decimal('5.00') (expecting $5.00 under the old
         DollarDecimal semantics) into 5 cents — data corruption with no
-        error. Reject at the boundary.
+        error. Bool is an ``int`` subclass, so ``True`` would otherwise
+        slip through as 1 (= 1 cent cap), the same class of bug #225
+        closed for ``DollarDecimal`` / ``FixedPointCount``. Reject at
+        the boundary (#243).
 
         int and int-shaped strings are fine (Pydantic coerces normally).
         """
+        if isinstance(v, bool):
+            raise ValueError(
+                "buy_max_cost must be int (cents), not bool — "
+                "bool is an int subclass, so True would otherwise slip "
+                "through as 1 (= 1 cent cap). Pass cents directly "
+                "(e.g., 500 for $5.00)."
+            )
         if isinstance(v, Decimal):
             raise ValueError(
                 "buy_max_cost must be int (cents), not Decimal. "

tests/test_models.py

@@ -871,6 +871,49 @@ def test_buy_max_cost_rejects_float(self) -> None:
                 buy_max_cost=5.0,  # type: ignore[arg-type]
             )
 
+    def test_buy_max_cost_rejects_bool(self) -> None:
+        """#243: bool inputs must raise — bool is an ``int`` subclass, so
+        ``True`` would otherwise slip through as ``1`` (= 1 cent cap), a
+        silent money-risk failure matching the #225 class of bug for
+        ``DollarDecimal`` / ``FixedPointCount``. A caller who passes a flag
+        (``risk_check_passed``, ``dry_run``) where cents were expected must
+        get a clear error, not a $0.01-capped order."""
+        from pydantic import ValidationError
+
+        from kalshi.models.orders import CreateOrderRequest
+
+        with pytest.raises(ValidationError, match=r"bool"):
+            CreateOrderRequest(
+                ticker="MKT",
+                side="yes",
+                action="buy",
+                count=1,
+                buy_max_cost=True,  # type: ignore[arg-type]
+            )
+        with pytest.raises(ValidationError, match=r"bool"):
+            CreateOrderRequest(
+                ticker="MKT",
+                side="yes",
+                action="buy",
+                count=1,
+                buy_max_cost=False,  # type: ignore[arg-type]
+            )
+
+    def test_buy_max_cost_accepts_plain_int(self) -> None:
+        """#243: regression — plain int (cents) still works."""
+        from kalshi.models.orders import CreateOrderRequest
+
+        req = CreateOrderRequest(
+            ticker="MKT",
+            side="yes",
+            action="buy",
+            count=1,
+            buy_max_cost=500,
+        )
+        assert req.buy_max_cost == 500
+        assert isinstance(req.buy_max_cost, int)
+        assert not isinstance(req.buy_max_cost, bool)
+
     def test_buy_max_cost_accepts_int_string(self) -> None:
         """Int-shaped strings are coerced normally (e.g., loading from env/config)."""
         from kalshi.models.orders import CreateOrderRequest