fixup! fixup! ⚡️(backend) implement etag and last_modified cache headers to fetch content

src/backend/core/api/viewsets.py

@@ -1971,7 +1971,16 @@ class DocumentViewSet(
         if_none_match = request.META.get("HTTP_IF_NONE_MATCH")  # contains ETag
         if_modified_since = request.META.get("HTTP_IF_MODIFIED_SINCE")
 
-        if if_none_match and if_none_match == etag:
+        # Normalize ETags for comparison: strip the W/ weak prefix and surrounding
+        # quotes. Proxies (e.g. nginx with gzip) convert strong ETags to weak ones,
+        # so a strict equality check would fail on production even when unchanged.
+        def _etag_value(tag):
+            if tag:
+                tag = tag.removeprefix("W/")
+                tag = tag.strip('"')
+            return tag
+
+        if if_none_match and _etag_value(if_none_match) == _etag_value(etag):
             return drf_response.Response(status=status.HTTP_304_NOT_MODIFIED)
 
         if if_modified_since:

src/backend/impress/settings.py

@@ -487,6 +487,7 @@ class Base(Configuration):
         "if-none-match",
         "if-modified-since",
     )
+    CORS_EXPOSE_HEADERS = ["ETag"]
 
     # Sentry
     SENTRY_DSN = values.Value(None, environ_name="SENTRY_DSN", environ_prefix=None)