feat(scheduling): retire replaced participant responses

src/govoplan_scheduling/backend/schemas.py

@@ -132,6 +132,20 @@ class SchedulingCandidateSlotReconcileInput(SchedulingCandidateSlotInput):
 
 class SchedulingParticipantReconcileInput(SchedulingParticipantInput):
     id: str | None = Field(default=None, max_length=36)
+    revision: str | None = Field(
+        default=None,
+        min_length=64,
+        max_length=64,
+        pattern=r"^[0-9a-f]{64}$",
+    )
+
+    @model_validator(mode="after")
+    def validate_existing_revision(self) -> "SchedulingParticipantReconcileInput":
+        if self.id is not None and self.revision is None:
+            raise ValueError("revision is required for an existing scheduling participant")
+        if self.id is None and self.revision is not None:
+            raise ValueError("revision can only be supplied for an existing scheduling participant")
+        return self
 
 
 class SchedulingRequestCreateRequest(BaseModel):
@@ -252,6 +266,7 @@ class SchedulingCandidateSlotResponse(BaseModel):
 
 class SchedulingParticipantResponse(BaseModel):
     id: str
+    revision: str | None = None
     is_current_participant: bool = False
     respondent_id: str | None = None
     display_name: str | None = None