Only one writeable campaign version at a time

server/app/mailer/persistence/campaigns.py

@@ -135,6 +135,12 @@ def create_campaign_version_from_json(
         session.add(campaign)
         session.flush()
     else:
+        current = session.get(CampaignVersion, campaign.current_version_id) if campaign.current_version_id else None
+        if current and not _version_is_audit_safe_snapshot(current):
+            raise CampaignPersistenceError(
+                f"Campaign already has active working version #{current.version_number}. "
+                "Continue editing or unlock that version instead of importing a parallel draft."
+            )
         campaign.name = config.campaign.name
         campaign.description = config.campaign.description
 
@@ -168,6 +174,24 @@ def _version_is_user_locked(version: CampaignVersion) -> bool:
     return _version_user_lock_state(version) is not None
 
 
+def _version_is_audit_safe_snapshot(version: CampaignVersion) -> bool:
+    return _version_user_lock_state(version) == "permanent" or version.workflow_state in {
+        CampaignVersionWorkflowState.QUEUED.value,
+        CampaignVersionWorkflowState.SENDING.value,
+        CampaignVersionWorkflowState.COMPLETED.value,
+        CampaignVersionWorkflowState.CANCELLED.value,
+        CampaignVersionWorkflowState.ARCHIVED.value,
+    }
+
+
+def _ensure_current_campaign_version(campaign: Campaign, version: CampaignVersion, *, action: str) -> None:
+    if campaign.current_version_id != version.id:
+        raise CampaignPersistenceError(
+            f"Historical campaign versions are read-only and cannot be used to {action}. "
+            "Open the current working version instead."
+        )
+
+
 def _version_is_validated_and_locked(version: CampaignVersion) -> bool:
     validation_summary = version.validation_summary if isinstance(version.validation_summary, dict) else {}
     return bool(version.locked_at and validation_summary.get("ok") is True and not _version_is_user_locked(version))
@@ -203,6 +227,7 @@ def validate_campaign_version(
     campaign = session.get(Campaign, version.campaign_id)
     if not campaign or campaign.tenant_id != tenant_id:
         raise CampaignPersistenceError("Campaign version is not accessible for this tenant")
+    _ensure_current_campaign_version(campaign, version, action="validate")
     if _version_is_user_locked(version) or version.workflow_state in {
         CampaignVersionWorkflowState.QUEUED.value,
         CampaignVersionWorkflowState.SENDING.value,
@@ -320,6 +345,7 @@ def build_campaign_version(
     campaign = session.get(Campaign, version.campaign_id)
     if not campaign or campaign.tenant_id != tenant_id:
         raise CampaignPersistenceError("Campaign version is not accessible for this tenant")
+    _ensure_current_campaign_version(campaign, version, action="build")
     if version.workflow_state == CampaignVersionWorkflowState.COMPLETED.value:
         raise CampaignPersistenceError("Sent campaign versions cannot be rebuilt")
     validation_summary = version.validation_summary if isinstance(version.validation_summary, dict) else {}