feat(latest): poll comix through the browser sidecar (#98)

comix.to began answering plain-TLS fetches with a Cloudflare JavaScript
challenge on 2026-08-12, so every poll got a 403 interstitial and its cover
host static.comix.to is gated the same way. comix joins kagane and novelfull
as a browser Site: one registry entry, no plain-TLS fallback, and cover bytes
routed through the browser's image path behind a fully pinned URL pattern.

The read is an in-tab fetch of the Series URL, not a DOM render: comix is an
SPA, so rendering costs ~65 requests for the same server-rendered HTML one
fetch returns (24.5 KB, ~480 ms). Parsers and stored Series identity are
untouched.

Verified live against the real browser unit: page 24793 bytes in one fetch,
chapter 53, cover accepted by the pin and 26862 image bytes retrieved by
direct navigation (comix's Series page sets cross-origin-embedder-policy:
require-corp, so an in-page fetch of the cover host cannot work).

backend/internal/latest/poller_test.go

@@ -762,6 +762,86 @@ func TestKaganeUsesBrowserFetcher(t *testing.T) {
 	}
 }
 
+// comix joined kagane behind the challenge on 2026-08-12 (#98): its page goes
+// to the browser, its Cover bytes go through the browser's image route because
+// static.comix.to is gated the same way, and the TLS fetcher is never asked
+// for either.
+func TestComixUsesBrowserFetcher(t *testing.T) {
+	s, dbURL := newTestStore(t)
+	const (
+		key       = "comix:n8we-dungeons-and-crayons"
+		seriesID  = "n8we-dungeons-and-crayons"
+		seriesURL = "https://comix.to/title/n8we-dungeons-and-crayons"
+		coverURL  = "https://static.comix.to/039d/i/1/34/6a6742bf15736@280.jpg"
+	)
+	if _, err := s.Upsert(s.OwnerID(), store.Bookmark{
+		Key: key, Site: "comix", SeriesID: seriesID, SeriesURL: seriesURL,
+		UpdatedAt: 1000,
+	}); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+	seedCoverSource(t, dbURL, "comix", seriesID, coverURL)
+
+	tlsF := &fakeFetcher{body: "", status: 200}
+	browserF := &fakeFetcher{body: comixSeriesFixture, status: 200}
+	covers := &fakeCoverFetcher{body: []byte("cover-bytes"), contentType: "image/jpeg"}
+	tlsCovers := &fakeBytesCoverFetcher{body: []byte("tls-bytes"), contentType: "image/jpeg"}
+	p := &Poller{
+		Store: s, Fetch: tlsF, BrowserFetch: browserF,
+		CoverFetch: covers, CoverBytesFetch: tlsCovers,
+		Now:      func() time.Time { return time.UnixMilli(5_000_000) },
+		Cooldown: time.Hour, BrowserCooldown: time.Hour,
+		Interval: time.Hour, Batch: 10,
+	}
+	p.runOnce(context.Background())
+
+	if len(tlsF.calls) != 0 {
+		t.Errorf("TLS fetcher was called for comix: %v", tlsF.calls)
+	}
+	if len(browserF.calls) != 1 {
+		t.Fatalf("browser fetcher calls = %v, want 1", browserF.calls)
+	}
+	if got := tlsCovers.callCount(); got != 0 {
+		t.Errorf("TLS cover fetches = %d, want 0: static.comix.to answers a challenge", got)
+	}
+	if got := covers.callCount(); got != 1 {
+		t.Fatalf("browser cover fetches = %d, want 1", got)
+	}
+	got, found, err := s.Get(s.OwnerID(), key)
+	if err != nil || !found {
+		t.Fatalf("Get: %v found=%v", err, found)
+	}
+	if got.LatestChapterNum == nil || *got.LatestChapterNum != 80 {
+		t.Errorf("LatestChapterNum = %v, want 80", got.LatestChapterNum)
+	}
+}
+
+// Without a browser, comix is skipped outright rather than handed to plain
+// TLS: a plain fetch retrieves only a challenge page (measured 2026-08-12).
+func TestComixSkippedWhenNoBrowserFetcher(t *testing.T) {
+	s, _ := newTestStore(t)
+	if _, err := s.Upsert(s.OwnerID(), store.Bookmark{
+		Key: "comix:n8we-dungeons-and-crayons", Site: "comix",
+		SeriesID:  "n8we-dungeons-and-crayons",
+		SeriesURL: "https://comix.to/title/n8we-dungeons-and-crayons",
+		UpdatedAt: 1000,
+	}); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+	f := &fakeFetcher{body: comixSeriesFixture, status: 200}
+	p := &Poller{
+		Store: s, Fetch: f,
+		Now:      func() time.Time { return time.UnixMilli(5_000_000) },
+		Cooldown: time.Hour, BrowserCooldown: time.Hour,
+		Interval: time.Hour, Batch: 10,
+	}
+	p.runOnce(context.Background())
+
+	if len(f.calls) != 0 {
+		t.Errorf("TLS fetcher was called for comix: %v", f.calls)
+	}
+}
+
 func TestRunOncePrefetchesKaganeCover(t *testing.T) {
 	s, dbURL := newTestStore(t)
 	const (