Poll comix.to through the browser sidecar (#98) (#105)

Closes #98.

comix.to began answering plain-TLS fetches with a Cloudflare JavaScript
challenge on 2026-08-12, so every poll got a 403 interstitial. Its cover host
`static.comix.to` is gated the same way. comix therefore joins kagane and
novelfull as a browser-backed Site.

## What changed

- **Registry** (`internal/latest/sites.go`): comix gains a `Browser` entry —
  `comixRead`, `Done: body != "" && !isInterstitial(body)`, `Fallback: false`.
  Skip-when-no-browser falls out of the existing routing; no site-string compare
  was added anywhere.
- **Read shape** (`internal/latest/browser.go`): an in-tab `fetch()` of the
  Series URL, not a DOM render. comix is an SPA — rendering it costs ~65
  requests for the same server-rendered HTML one fetch returns (24.5 KB,
  ~480 ms measured). `comixSeriesPageURL` pins scheme + host + `/title/<slug>`
  and rebuilds the address, so a client-supplied `series_url` cannot aim the
  browser anywhere else.
- **Cover bytes**: `comixImageURLRe` pins `https://static.comix.to/<path>.<ext>`;
  `BrowserFetcher.Image` now gates on `browserOnlyCoverURL` rather than a
  kagane-only regex, so both Sites' image URLs route through the one path.
  Bytes come from direct navigation, not a page-context fetch — comix's Series
  page sets `cross-origin-embedder-policy: require-corp`, which fails one.
- **Parsers and stored Series identity: untouched.** The in-tab body is the same
  server-rendered HTML the existing fixtures were cut from.

## Verification

- `go test ./...` green (needs Docker).
- New seam tests: comix routes to the browser when one is configured, and is
  not fetched at all when none is (`TestComixUsesBrowserFetcher`,
  `TestComixSkippedWhenNoBrowserFetcher`); URL-pin and cover-gate table tests.
- Live proof against the real browser unit, `TestSmokeComix` (env-gated):
  page 24793 bytes in one in-tab fetch, chapter 53, cover accepted by the pin,
  26862 bytes of `image/jpg` retrieved.
- Two-axis review run; findings were stale comments on `BrowserFetcher`, `Get`
  and the `Fallback` field, fixed in f000cc7.

Docs updated: root `AGENTS.md` (constraint + smoke command, including the note
that this dev machine's ISP DNS-hijacks `comix.to`), `backend/AGENTS.md`
(poller, cover pipeline, `BROWSER_WS_URL`), `REDEPLOY.md` §8 degrade note.

Reviewed-on: #105
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

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 (