Replace the one-event placeholder (subscribe_stream_from_envelope +
envelope_to_sse_stream, which called invoke() and wrapped the single
ResponseEnvelope) with the real streaming path: subscribe_handler now
calls GatewayDispatch::invoke_streaming() and pipes the
BoxStream<ResponseEnvelope> to SSE via subscribe_stream_from_envelope_stream
(futures::StreamExt::map). Each Ok(output) becomes a data: frame; each
Err becomes an event:error frame (terminal — stream ends after it);
natural stream end closes the SSE. Internal ops still return a single
NOT_FOUND error event via subscribe_stream_internal_error (kept). Client
disconnect drops the stream via Rust's Drop (abort cascade per ADR-016).
glm-5.2
9e4d17b1c5