refactor: four small cleanups from the review pass (#3072)

Items 2-5 of #3072. Item 1 (the per-row sweep inserts) is separate.

2. .fc-bad was not merely duplicated — it is .fc-weak under a second
   name. Both local definitions were `color: rgb(var(--v-theme-error))`,
   identical to the global .fc-weak, and GpuAgentCard was already using
   .fc-weak to colour exactly what GpuActivityPanel coloured .fc-bad (an
   errored count, red when non-zero). So rather than promoting a synonym
   to app.css, both call sites now use .fc-weak and the local defs are
   gone. app.css's status-colour comment records why there is no .fc-bad,
   next to the existing note on why .fc-ok is deliberately NOT global.

3. GalleryItem.vue's obsidian literals now use --v-theme-background,
   which IS obsidian (vuetify-theme.js maps background -> surfaces.
   obsidian). Preferred over --fc-chrome-rgb: same value, but that
   variable is named for the nav fade, not for the palette entry.

   The ticket said these were the only three real uses in the tree. They
   are not — GalleryItem itself had two more in the artist-label
   gradient (fixed here, so the file is now consistent), and ~13 more
   live in SeriesView, SeriesReaderView, ImageViewer, ArtistHeader,
   ExploreView and GalleryFilterBar. Those are a separate sweep, filed
   rather than folded in here.

4. The attachment download path had two hand-formatted copies. One
   definition now, `attachment_download_url`, next to the model both
   serializers already import. The test pins it by MATCHING the built
   path against the app's real URL map rather than comparing to a
   literal — a string-equality test would still pass after someone
   renamed the route, which is the drift the helper exists to prevent.

5. Extension API key now compares with hmac.compare_digest. Compared as
   BYTES, not str: compare_digest's str form raises TypeError on
   non-ASCII, and this value comes straight from an attacker-controlled
   header, so the str form would turn a junk key into a 500 instead of a
   403. Low stakes either way — the API is unauthenticated-by-design on
   a LAN — but it costs nothing.

Refs #3072

backend/app/api/extension.py

@@ -6,6 +6,7 @@ from __future__ import annotations
 
 import asyncio
 import hashlib
+import hmac
 import re
 from pathlib import Path
 
@@ -41,7 +42,15 @@ async def _ext_key_required(session) -> bool:
     stored = (await session.execute(
         select(AppSetting.value).where(AppSetting.key == "extension_api_key")
     )).scalar_one_or_none()
-    return stored is not None and supplied == stored
+    if stored is None:
+        return False
+    # compare_digest, not `==`: the stored key is a shared secret, and a
+    # short-circuiting compare leaks its prefix through timing. Costs nothing
+    # here — it is not that this route is exposed (#3072). Compared as BYTES:
+    # compare_digest's str form rejects non-ASCII with TypeError, and this
+    # header is attacker-supplied, so a str compare would turn a junk key into
+    # a 500 instead of a 403.
+    return hmac.compare_digest(supplied.encode("utf-8"), stored.encode("utf-8"))
 
 
 def _extract_version(xpi_name: str) -> str:

backend/app/models/__init__.py

@@ -27,7 +27,7 @@ from .patreon_seen_media import PatreonSeenMedia
 from .pixiv_failed_media import PixivFailedMedia
 from .pixiv_seen_media import PixivSeenMedia
 from .post import Post
-from .post_attachment import PostAttachment
+from .post_attachment import PostAttachment, attachment_download_url
 from .presentation_review import PresentationReview
 from .series_chapter import SeriesChapter
 from .series_page import SeriesPage
@@ -58,6 +58,7 @@ __all__ = [
     "SubscribeStarSeenMedia",
     "Post",
     "PostAttachment",
+    "attachment_download_url",
     "PresentationReview",
     "SeriesChapter",
     "SeriesPage",

backend/app/models/post_attachment.py

@@ -65,3 +65,15 @@ class PostAttachment(Base):
     captured_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now()
     )
+
+
+def attachment_download_url(attachment_id: int) -> str:
+    """The path that streams this attachment's bytes.
+
+    Both serializers that expose an attachment to the frontend
+    (`provenance_service`, `post_feed_service`) built this literal themselves,
+    so changing the route in `api/attachments.py` meant two edits and only one
+    would be remembered (#3072). `test_attachment_download_url` pins it against
+    the app's registered rule, so the drift is caught rather than trusted to.
+    """
+    return f"/api/attachments/{attachment_id}/download"

backend/app/services/post_feed_service.py

@@ -24,6 +24,7 @@ from ..models import (
     Post,
     PostAttachment,
     Source,
+    attachment_download_url,
 )
 from ..utils.html_sanitize import (
     extract_img_srcs,
@@ -360,7 +361,7 @@ class PostFeedService:
                 "ext": att.ext,
                 "mime": att.mime,
                 "size_bytes": att.size_bytes,
-                "download_url": f"/api/attachments/{att.id}/download",
+                "download_url": attachment_download_url(att.id),
             })
         return out
 

backend/app/services/provenance_service.py

@@ -16,6 +16,7 @@ from ..models import (
     Post,
     PostAttachment,
     Source,
+    attachment_download_url,
 )
 from ..utils.html_sanitize import sanitize_post_html
 
@@ -53,7 +54,7 @@ def _attachment_dict(a: PostAttachment) -> dict:
         "original_filename": a.original_filename,
         "size_bytes": a.size_bytes,
         "ext": a.ext,
-        "download_url": f"/api/attachments/{a.id}/download",
+        "download_url": attachment_download_url(a.id),
     }
 
 

frontend/src/components/gallery/GalleryItem.vue

@@ -139,9 +139,9 @@ function onThumbError() { thumbError.value = true }
   position: absolute; top: 8px; left: 8px;
   width: 22px; height: 22px; border-radius: 4px;
   border: 2px solid rgba(232, 228, 216, 0.8);
-  background: rgba(20, 23, 26, 0.45);
+  background: rgba(var(--v-theme-background), 0.45);
   display: grid; place-items: center;
-  color: #14171A; z-index: 11;
+  color: rgb(var(--v-theme-background)); z-index: 11;
 }
 .fc-gallery-item__checkbox.on {
   background: rgb(var(--v-theme-accent));
@@ -152,7 +152,7 @@ function onThumbError() { thumbError.value = true }
   min-width: 22px; height: 22px; padding: 0 5px;
   border-radius: 11px;
   background: rgb(var(--v-theme-accent));
-  color: #14171A; font-size: 12px; font-weight: 700;
+  color: rgb(var(--v-theme-background)); font-size: 12px; font-weight: 700;
   display: grid; place-items: center; z-index: 11;
   pointer-events: none;
 }
@@ -160,7 +160,8 @@ function onThumbError() { thumbError.value = true }
   position: absolute; left: 0; right: 0; bottom: 0;
   padding: 14px 8px 6px;
   background: linear-gradient(
-    to top, rgba(20, 23, 26, 0.78), rgba(20, 23, 26, 0)
+    to top, rgba(var(--v-theme-background), 0.78),
+    rgba(var(--v-theme-background), 0)
   );
   font-size: 12px; line-height: 1.2;
   white-space: nowrap; overflow: hidden; text-overflow: ellipsis;

frontend/src/components/settings/DownloadsActivityPanel.vue

@@ -35,7 +35,7 @@
         All subscription sources healthy.
       </p>
       <p v-else class="text-body-2 mb-0">
-        <b class="fc-bad">{{ failing.length }}</b> failing source(s):
+        <b class="fc-weak">{{ failing.length }}</b> failing source(s):
         <span class="fc-muted">{{ failingNames }}</span>
       </p>
     </v-card-text>
@@ -72,5 +72,4 @@ onUnmounted(() => { if (pollId) clearInterval(pollId) })
 </script>
 
 <style scoped>
-.fc-bad { color: rgb(var(--v-theme-error)); }
 </style>

frontend/src/components/settings/GpuActivityPanel.vue

@@ -25,7 +25,7 @@
           <div class="fc-cell__l">done</div>
         </div>
         <div class="fc-cell">
-          <div class="fc-cell__n" :class="q.error ? 'fc-bad' : ''">{{ q.error }}</div>
+          <div class="fc-cell__n" :class="q.error ? 'fc-weak' : ''">{{ q.error }}</div>
           <div class="fc-cell__l">errored</div>
         </div>
       </div>
@@ -104,5 +104,4 @@ onUnmounted(() => { if (pollId) clearInterval(pollId) })
   font-size: 11px; text-transform: uppercase; letter-spacing: 0.04em;
   color: rgb(var(--v-theme-on-surface-variant));
 }
-.fc-bad { color: rgb(var(--v-theme-error)); }
 </style>

frontend/src/styles/app.css

@@ -50,7 +50,12 @@
 
 /* Status text colours (DRY pass #161): fc-good = success, fc-weak = error,
    consolidated from the GPU / heads cards. fc-ok is intentionally NOT global —
-   it means on-surface in HeadsCard but success in QueuesTable. */
+   it means on-surface in HeadsCard but success in QueuesTable.
+
+   No `.fc-bad` (#3072): it was defined locally and identically in the Downloads
+   and GPU activity panels, and it is fc-weak under a second name — GpuAgentCard
+   and GpuActivityPanel were colouring the same "errored" count with different
+   class names. Both now use fc-weak. Reach for fc-weak, not a new synonym. */
 .fc-good { color: rgb(var(--v-theme-success)); }
 .fc-weak { color: rgb(var(--v-theme-error)); }
 

tests/test_api_attachments.py

@@ -1,6 +1,6 @@
 import pytest
 
-from backend.app.models import Artist, PostAttachment
+from backend.app.models import Artist, PostAttachment, attachment_download_url
 
 pytestmark = pytest.mark.integration
 
@@ -33,3 +33,16 @@ async def test_download_streams_with_disposition(client, db, tmp_path):
 async def test_download_404(client):
     resp = await client.get("/api/attachments/999999/download")
     assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_attachment_download_url_routes_to_the_download_endpoint(app):
+    """The two serializers no longer hand-format this path (#3072) — but a
+    single definition is only worth having if it still matches the route. Pin
+    it by MATCHING against the real URL map rather than comparing to a literal:
+    a string equality test would pass just as happily after someone renamed the
+    route, which is the exact drift the helper exists to prevent."""
+    built = attachment_download_url(4242)
+    endpoint, args = app.url_map.bind("localhost").match(built)
+    assert endpoint == "attachments.download"
+    assert args == {"attachment_id": 4242}