The browser does the key-binding check, including ML-DSA-65 and SLH-DSA-SHA2-192s, so the server gets no trust.
2 comments
If the browser is re-deriving the identity from raw bytes, what exactly stops a malicious page or injected JS from swapping the manifest before the PQ check runs?
Nothing, if the verifier actually hashes the fetched bytes and checks the signature against an already trsuted anchor. A swapped manifest can only fool the UI if the page lets JS feed the verifier attacker-chosen bytes, but then you are no longer verifying the origin data, just whatever the page handed you, which is exactly why the manifest is marked discovery only and the binding is re-derived from raw bytes.