As handleRaw, but dispatched against an explicit per-request
ConnectionState (for the Streamable HTTP batch back-compat path, which
resolves the request's session/per-request state in the transport). The
batch version gate and per-message dispatch both consult conn instead of
the single bound activeConnection, so a session that negotiated 2025-03-26
can actually reach the legacy batch path and a modern session is gated on its
own negotiated version. null falls back to the no-arg behaviour.
As handleRaw, but dispatched against an explicit per-request ConnectionState (for the Streamable HTTP batch back-compat path, which resolves the request's session/per-request state in the transport). The batch version gate and per-message dispatch both consult conn instead of the single bound activeConnection, so a session that negotiated 2025-03-26 can actually reach the legacy batch path and a modern session is gated on its own negotiated version. null falls back to the no-arg behaviour.