Avatars: a sender without one logged a console error; phone list rows spaced 20px

A missing avatar was a 404, which the browser reports as an error for every
such sender on every page. It is now an empty 204: the <img> still fails to
decode it and the initials show through, but nothing is logged, and the miss
carries the same one-day browser cache as a hit so it stops being re-fetched.

On a phone the mail list's rows sit 20px apart instead of 7px.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/api/avatar.py

@@ -3,8 +3,9 @@
 The browser only ever calls ``GET /api/avatar`` (same origin), so a sender can never
 see the user's IP or read activity: the server does the outbound fetch under the
 §10.6 SSRF guard and caches the result (both hits and misses) in Redis. A miss
-returns 404, which the UI renders as its initials avatar. Disable with
-``SENDER_AVATARS_ENABLED=false``.
+returns 204 No Content: the <img> fails to decode it and the UI falls back to its
+initials, without the browser logging an error for every sender who has no avatar
+(a 404 did, filling the console). Disable with ``SENDER_AVATARS_ENABLED=false``.
 """
 
 from __future__ import annotations
@@ -25,6 +26,12 @@ _CACHE_TTL_HIT = 7 * 24 * 3600  # remember a found avatar for a week
 _CACHE_TTL_MISS = 24 * 3600  # re-check "no avatar" daily
 _MAX_BYTES = 200 * 1024
 _NONE = b"none"
+# The browser keeps an answer as long as we would, so it stops re-asking per page.
+_BROWSER_CACHE = {"Cache-Control": "private, max-age=86400"}
+
+
+def _no_avatar() -> Response:
+    return Response(status_code=204, headers=_BROWSER_CACHE)
 
 
 def _email_md5(email: str) -> str:
@@ -64,29 +71,27 @@ async def _resolve(email: str, md5: str) -> tuple[str, bytes] | None:
 async def sender_avatar(_user: CurrentUser, email: str = Query(...)) -> Response:
     email = email.strip().lower()
     if not get_settings().sender_avatars_enabled or "@" not in email:
-        return Response(status_code=404)
+        return _no_avatar()
 
     # Binary-safe client: the cache holds raw image bytes (and a b"none" marker).
     redis = get_redis_bytes()
     md5 = _email_md5(email)
     key = f"avatar:{md5}"
-    headers = {"Cache-Control": "private, max-age=86400"}
-
     cached: bytes | None = await redis.get(key)
     if cached == _NONE:
-        return Response(status_code=404)
+        return _no_avatar()
     if cached:
         cached_ctype, _, cached_body = cached.partition(b"\n")
         return Response(
             content=cached_body,
             media_type=cached_ctype.decode("ascii", "ignore"),
-            headers=headers,
+            headers=_BROWSER_CACHE,
         )
 
     result = await _resolve(email, md5)
     if result is None:
         await redis.set(key, _NONE, ex=_CACHE_TTL_MISS)
-        return Response(status_code=404)
+        return _no_avatar()
     ctype, body = result
     await redis.set(key, ctype.encode("ascii", "ignore") + b"\n" + body, ex=_CACHE_TTL_HIT)
-    return Response(content=body, media_type=ctype, headers=headers)
+    return Response(content=body, media_type=ctype, headers=_BROWSER_CACHE)

backend/tests/api/test_avatar.py

@@ -2,7 +2,7 @@
 
 The shared Redis client decodes replies as text, so the cache of raw image
 bytes broke on the second request for any sender — a 500 instead of the image
-(or instead of the 404 that means "draw initials").
+(or instead of the 204 that means "draw initials").
 """
 
 from __future__ import annotations
@@ -68,7 +68,7 @@ async def test_cached_avatar_is_served_again(
     assert calls == 1  # the second came from the cache
 
 
-async def test_cached_miss_is_a_404_again(
+async def test_cached_miss_is_a_204_again(
     client: httpx.AsyncClient, monkeypatch: pytest.MonkeyPatch
 ) -> None:
     calls = 0
@@ -81,5 +81,8 @@ async def test_cached_miss_is_a_404_again(
     monkeypatch.setattr(avatar, "_resolve", fake_resolve)
     for _ in range(2):
         resp = await client.get("/api/avatar", params={"email": "nobody@example.com"})
-        assert resp.status_code == 404
+        # 204, not 404: a miss is the normal case, and a 404 put a console
+        # error in the browser for every sender without an avatar.
+        assert resp.status_code == 204
+        assert "max-age" in resp.headers["cache-control"]
     assert calls == 1