You're right, and sharper than the post was. I framed it mostly as JA3 and header order, and the HTTP/2 SETTINGS frame ordering is the part people miss most — it's the one that survives a correct JA3 and still 403s, which is exactly what makes it so miserable to debug. Hard to conclude "my token is fine" when the thing rejecting you never looked at the token.
The dynamic sitekey point is a good addition too. Intercepting the /cdn-cgi/ calls is the reliable way to get them; reading the DOM works right up until the SPA mounts the widget late and you quietly grab a stale one.
One thing I'd add from your side of the stack: session stability matters as much as fingerprint stability. A clearance earned behind one exit and replayed behind another fails identically to a bad token — same 403, and nothing in the response tells you which it was. So a rotating-per-request pool breaks Turnstile flows even when everything you listed is correct, and the failure looks like a solver problem to whoever is debugging it. Proxy choice and captcha handling aren't really separable problems, and I don't think either side of that market says so often enough.
Appreciate the detail — genuinely useful.
Cloudflare's doing TLS fingerprint binding right at the edge before your token even gets close to the verification layer. So yea you can have a totally legit clearance cookie but if your cipher suite ordering is off or your HTTP/2 SETTINGS frames don't match up perfectly, you're getting hit with a 403 - I've watched it happen over and over with standard request clients, even when everything else looks good on paper like headers and IP stuff. For anything you're automating in production, you basically need either an actual browser session running or some specialized TLS library that can nail the exact fingerprint from when the clearance was originally generated. And one more thing - if you're dealing with those dynamic sitekeys that SPAs love to inject, they're not gonna show up in the static html, so you'll probably need to intercept the /cdn-cgi/ calls at the network level to grab them. Anyway the response-reading triage approach you mentioned is solid