feat(postbox): expose configurable protection contracts

src/govoplan_core/core/postbox.py

@@ -172,6 +172,10 @@ class PostboxDirectoryEntryRef:
     template_revision_id: str | None = None
     holder_count: int = 0
     vacant: bool = True
+    encryption_profile: str = "plaintext_v1"
+    key_epoch: int = 1
+    encryption_vault_id: str | None = None
+    protection_policy: Mapping[str, object] = field(default_factory=dict)
     access: PostboxAccessDecisionRef | None = None
     resource_revision: int = 1
     etag: str | None = None
@@ -260,6 +264,9 @@ class PostboxMessageAuthoringRequest:
     idempotency_key: str
     subject: str
     body_text: str | None = None
+    ciphertext_ref: str | None = None
+    signed_manifest_ref: str | None = None
+    wrapped_keys: tuple[PostboxWrappedKeyRef, ...] = ()
     classification: str = "internal"
     participants: tuple[PostboxParticipantRef, ...] = ()
     attachments: tuple[PostboxAttachmentRef, ...] = ()