Gateway cross-routing trust and upstream re-encoding

Auto-cross-routing is untrusted whenever no explicit provider/upstream override exists and either protocol or origin changes. Such routes must re-encode the parsed request rather than replaying client compression, since foreign providers may reject codecs such as zstd. Preserve client encoding only for native passthrough with identical protocol and origin, or explicit X-Lore-Provider/X-Lore-Upstream-URL overrides; Vertex and Bedrock are provider-tagged. Empty, absent, and identity remain uncompressed. Forwarded Content-Length must describe emitted bytes, never reuse the client header. A protocol-only trust predicate is unsafe because same-protocol reroutes can still target a foreign origin.