fix(multimodal): gate vLLM RDMA emit on exporter presence, not request mode

resolve_mm_rdma_enabled required the per-request transport mode to be `rdma`,
but the exporter is built whenever the lane is enabled — including via the
legacy `SMG_MM_PIXEL_RDMA` flag, which leaves the mode at the default `inline`.
That combination built the exporter and let the worker advertise
supports_rdma_pull=true, yet the gateway never emitted `remote` payloads.

Gate purely on the exporter being present plus the worker's capability label,
matching TokenSpeed (which emits whenever the exporter is up) and honoring every
way the lane is enabled. The capability label is the per-worker opt-out. Drop
the bogus `_mode` label from the test (mode is no longer read; the exporter gate
is now exercised directly). (Codex, CodeRabbit)

Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>

Author: slin1237

model_gateway/src/routers/grpc/multimodal/transport.rs

@@ -155,17 +155,17 @@ pub(super) fn resolve_mm_shm_min_bytes(workers: Option<&WorkerSelection>) -> usi
 }
 
 /// Resolve whether vLLM `pixel_values` may use the RDMA lane for this request: the
-/// resolved transport mode is `rdma`, the gateway exporter is up, and the worker
-/// advertises it can pull. The capability gate keeps SMG from emitting a `remote`
-/// payload to a worker that would reject it. The exporter is a process-wide
-/// resource (NIXL agent + arena), so a per-worker mode override can gate RDMA off
-/// but cannot turn it on without the router-level transport mode / env.
+/// gateway exporter is up and the worker advertises it can pull. The capability
+/// gate keeps SMG from emitting a `remote` payload to a worker that would reject
+/// it, and is the per-worker opt-out (a worker that shouldn't RDMA reports
+/// `supports_rdma_pull=false`).
+///
+/// The exporter is a process-wide resource built once the RDMA lane is enabled
+/// (router transport mode `rdma`, `SMG_MM_TENSOR_TRANSPORT=rdma`, or the legacy
+/// `SMG_MM_PIXEL_RDMA`). Gating on its presence — rather than the per-request
+/// transport mode — matches TokenSpeed and honors every way the lane is enabled.
 pub(super) fn resolve_mm_rdma_enabled(workers: Option<&WorkerSelection>) -> bool {
-    let mode =
-        worker_transport_mode_override(workers).unwrap_or_else(|| mm_transport_defaults().mode);
-    mode == TransportMode::Rdma
-        && mm_rdma_exporter().is_some()
-        && worker_supports_rdma_pull(workers)
+    mm_rdma_exporter().is_some() && worker_supports_rdma_pull(workers)
 }
 
 /// Whether the request's worker advertises RDMA-pull support via the
@@ -666,8 +666,7 @@ mod tests {
     fn resolve_mm_rdma_enabled_requires_exporter() {
         // Even a capable worker cannot RDMA without the gateway exporter, which is
         // never built in the default (stub) test build -> the gate stays off.
-        let workers =
-            single_worker_with_labels(&[("supports_rdma_pull", "true"), ("_mode", "unused")]);
+        let workers = single_worker_with_labels(&[("supports_rdma_pull", "true")]);
         assert!(!resolve_mm_rdma_enabled(Some(&workers)));
     }