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/sites.go

@@ -248,14 +248,25 @@ var comixInitialDataRe = regexp.MustCompile(`(?is)<script\b[^>]*\bid\s*=\s*["']i
 // supplied, and a headless browser is a strong SSRF primitive.
 var kaganeImageURLRe = regexp.MustCompile(`^https://kagane\.to/api/v2/image/([0-9a-f-]{36})/compressed$`)
 
+// comixImageURLRe matches comix's cover host and path shape. Pinned in full
+// (scheme, host, path characters, image extension) for the same reason
+// kaganeImageURLRe is: the address reaches a headless browser, and it can
+// originate in a client-supplied PUT body. No dot is allowed inside the path,
+// so no traversal or second extension can hide in it. Shape from a live page,
+// 2026-08-10: /039d/i/1/34/6a6742bf15736@280.jpg.
+var comixImageURLRe = regexp.MustCompile(`^https://static\.comix\.to/[A-Za-z0-9@/_-]+\.(?:jpg|jpeg|png|webp)$`)
+
 // browserOnlyCoverURL reports whether the browser sidecar is the only fetcher
 // for cover bytes at imageURL. kagane's image route answers a plain fetch with
-// a challenge and `cross-origin-resource-policy: same-origin`, so a TLS fetch
-// would only ever retrieve a challenge page and must not be attempted
-// (ADR-0007). This is the byte-fetch router's per-Site knowledge; it lives in
-// the extraction module, which owns kagane's URL shapes.
+// a challenge and `cross-origin-resource-policy: same-origin`, and
+// static.comix.to answers one with the same Cloudflare challenge its pages
+// serve (measured 2026-08-12, issue #98), so a TLS fetch would only ever
+// retrieve a challenge page and must not be attempted (ADR-0007). This is the
+// byte-fetch router's per-Site knowledge; it lives in the extraction module,
+// which owns those URL shapes.
 func browserOnlyCoverURL(imageURL string) bool {
-	return kaganeImageURLRe.MatchString(imageURL)
+	return kaganeImageURLRe.MatchString(imageURL) ||
+		comixImageURLRe.MatchString(imageURL)
 }
 
 // kagane's browser-fetched series response publishes cover image IDs under
@@ -389,6 +400,15 @@ var sites = map[string]site{
 		Host:          "comix.to",
 		LatestChapter: comixLatestChapter,
 		Cover:         comixCoverEntry,
+		Browser: &browserRead{
+			Read: comixRead,
+			// The interstitial is served in place of the page, so "arrived"
+			// has to exclude it explicitly, as novelfull's does.
+			Done: func(body string) bool { return body != "" && !isInterstitial(body) },
+			// Never falls back: a plain fetch of a comix page or cover
+			// retrieves only a challenge page (measured 2026-08-12).
+			Fallback: false,
+		},
 	},
 	"kagane": {
 		Host:          "kagane.to",