feat: harden campaign delivery and editing

src/govoplan_campaign/backend/routes/versions.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 
-from fastapi import APIRouter, Depends, HTTPException, Query, status
+from fastapi import APIRouter, Depends, Header, HTTPException, Query, Response, status
 from sqlalchemy.orm import Session
 
 from govoplan_campaign.backend.schemas import (
@@ -101,6 +101,7 @@ def list_versions(
 def get_version_detail(
     campaign_id: str,
     version_id: str,
+    response: Response,
     session: Session = Depends(get_session),
     principal: ApiPrincipal = Depends(require_scope("campaigns:campaign:read")),
 ):
@@ -113,10 +114,12 @@ def get_version_detail(
             campaign_id=campaign_id,
             version_id=version_id,
         )
-        return CampaignVersionDetailResponse.model_validate(
+        result = CampaignVersionDetailResponse.model_validate(
             version,
             context=_campaign_response_context(principal),
         )
+        response.headers["ETag"] = version.strong_etag
+        return result
     except CampaignPersistenceError as exc:
         raise HTTPException(
             status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)
@@ -335,18 +338,23 @@ def update_version_detail(
     campaign_id: str,
     version_id: str,
     payload: CampaignVersionUpdateRequest,
+    response: Response,
+    if_match: str | None = Header(default=None, alias="If-Match"),
     session: Session = Depends(get_session),
     principal: ApiPrincipal = Depends(require_scope("campaigns:campaign:update")),
 ):
-    return _update_campaign_version_detail_response(
+    result = _update_campaign_version_detail_response(
         session,
         principal,
         campaign_id,
         version_id,
         payload,
+        if_match=if_match,
         autosave=False,
         audit_action="campaign.version_updated",
     )
+    response.headers["ETag"] = result.strong_etag
+    return result
 
 
 @router.post(
@@ -357,18 +365,23 @@ def autosave_version(
     campaign_id: str,
     version_id: str,
     payload: CampaignVersionUpdateRequest,
+    response: Response,
+    if_match: str | None = Header(default=None, alias="If-Match"),
     session: Session = Depends(get_session),
     principal: ApiPrincipal = Depends(require_scope("campaigns:campaign:update")),
 ):
-    return _update_campaign_version_detail_response(
+    result = _update_campaign_version_detail_response(
         session,
         principal,
         campaign_id,
         version_id,
         payload,
+        if_match=if_match,
         autosave=True,
         audit_action="campaign.version_autosaved",
     )
+    response.headers["ETag"] = result.strong_etag
+    return result
 
 
 @router.post(