malkhut(T1): scaffold — frozen state model, actions, features, engine

T1 scaffold: 42 frozen dataclasses (state.py), action model + PlannedPolicy +
RiskDecision (actions.py), 17-feature extraction (features.py),
FulfilmentEngine hot-path orchestrator (engine.py).

MALKHUT/malkhut/actions.py

@@ -0,0 +1,59 @@
+"""
+Action model — compact menu for simultaneous-move tree search.
+
+Bad: enumerate every price tick x every quantity x every TTL x every TIF.
+Good: 8-24 meaningful actions per player, 3-12 per counterparty role.
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Mapping, Optional, Tuple
+
+from malkhut.state import ActionKind, AgentRole, OrderType, Side
+
+
+@dataclass(frozen=True, slots=True)
+class FulfilmentAction:
+    """One atomic action candidate."""
+    kind: ActionKind
+    side: Optional[Side]
+    order_type: Optional[OrderType]
+    price_ticks_from_best: int
+    qty_fraction: float
+    ttl_ms: int
+    cancel_order_id: Optional[str] = None
+    reduce_only: bool = False
+    post_only: bool = False
+    metadata: Mapping[str, Any] = field(default_factory=dict)
+
+
+@dataclass(frozen=True, slots=True)
+class CounterpartyAction:
+    """Adversarially useful aggregate actions that alter book/fill outcomes."""
+    role: AgentRole
+    kind: ActionKind
+    side: Optional[Side]
+    price_ticks_from_best: int
+    qty_fraction_of_top: float
+    toxicity: float = 0.0
+    metadata: Mapping[str, Any] = field(default_factory=dict)
+
+
+JointAction = Tuple[Any, ...]  # (our_action, cp_action_1, cp_action_2, ...)
+
+
+@dataclass(frozen=True, slots=True)
+class PlannedPolicy:
+    """Output of the planner: distribution over actions + selected action."""
+    actions: Tuple[FulfilmentAction, ...]
+    probabilities: Tuple[float, ...]
+    selected_action: FulfilmentAction
+    diagnostics: Mapping[str, Any]
+
+
+@dataclass(frozen=True, slots=True)
+class RiskDecision:
+    approved: bool
+    action: Optional[FulfilmentAction]
+    reason: str
+    adjusted: bool = False