M0 + M1 done

RI/src/emcp_bus/pdp/models.py

@@ -0,0 +1,28 @@
+"""PDP decision contract (EP-03-T04).
+
+Every response from the PDP is one of these three outcomes, never a bare
+boolean -- `policy_version` and `reason_code` are mandatory so the Gateway's
+audit trail (EP-08-T02) and end-to-end correlation (EP-08-T03, RF-17) always
+have something to point at, and so a REQUIRE_APPROVAL is never collapsed
+into ALLOW/DENY by a caller that only checks truthiness.
+"""
+
+from __future__ import annotations
+
+from enum import StrEnum
+
+from pydantic import BaseModel
+
+
+class PDPOutcome(StrEnum):
+    ALLOW = "ALLOW"
+    DENY = "DENY"
+    REQUIRE_APPROVAL = "REQUIRE_APPROVAL"
+
+
+class PDPDecision(BaseModel):
+    outcome: PDPOutcome
+    policy_version: str
+    reason_code: str
+    """Machine-readable reason, e.g. NOT_IN_ENTITLEMENT, TRANSACTION_POLICY_DENIED,
+    APPROVAL_THRESHOLD_EXCEEDED, ALLOWED, PDP_UNAVAILABLE (README.md §27)."""