feat: extend calendar scheduling reconciliation contract

docs/MODULE_ARCHITECTURE.md

@@ -217,6 +217,12 @@ Other stable runtime capabilities currently include:
 - `payments.requests`
 - `workflow.definitionContributions` and `workflow.runtimeWorker`
 
+`calendar.scheduling` keeps workflow modules independent of Calendar-owned
+models and transport adapters. Consumers may create tentative events, promote
+the selected event in place, and release unused events idempotently. The
+provider returns bounded external-delivery and outbox references so consumers
+can retain retry state without copying Calendar's synchronization internals.
+
 `application_status.projection` lets a presentation module resolve the tenant
 and display or request access to an owner-supplied, deliberately bounded
 applicant-status view. The provider retains policy, authorization, token, and

src/govoplan_core/core/calendar.py

@@ -45,6 +45,15 @@ class CalendarEventRef:
     outbox_operation_id: str | None = None
 
 
+@dataclass(frozen=True, slots=True)
+class CalendarEventReleaseRef:
+    event_id: str
+    accepted: bool = True
+    already_released: bool = False
+    external_state: str = "local_released"
+    outbox_operation_id: str | None = None
+
+
 @dataclass(frozen=True, slots=True)
 class CalendarInvitationAttendeeRequest:
     address: str
@@ -156,6 +165,27 @@ class CalendarSchedulingProvider(Protocol):
     ) -> CalendarEventRef:
         ...
 
+    def promote_event(
+        self,
+        session: object,
+        *,
+        tenant_id: str,
+        user_id: str | None,
+        event_id: str,
+        request: CalendarEventRequest,
+    ) -> CalendarEventRef:
+        ...
+
+    def release_event(
+        self,
+        session: object,
+        *,
+        tenant_id: str,
+        user_id: str | None,
+        event_id: str,
+    ) -> CalendarEventReleaseRef:
+        ...
+
 
 @runtime_checkable
 class CalendarOutboxProvider(Protocol):