[router] refactor router and worker management 4/n (#10756)

Co-authored-by: Chang Su <chang.s.su@oracle.com>

sgl-router/src/routers/http/router.rs

@@ -35,6 +35,7 @@ pub struct Router {
     policy_registry: Arc<PolicyRegistry>,
     client: Client,
     dp_aware: bool,
+    enable_igw: bool,
     retry_config: RetryConfig,
     _worker_loads: Arc<tokio::sync::watch::Receiver<HashMap<String, isize>>>,
     _load_monitor_handle: Option<Arc<tokio::task::JoinHandle<()>>>,
@@ -93,6 +94,7 @@ impl Router {
             policy_registry: ctx.policy_registry.clone(),
             client: ctx.client.clone(),
             dp_aware: ctx.router_config.dp_aware,
+            enable_igw: ctx.router_config.enable_igw,
             retry_config: ctx.router_config.effective_retry_config(),
             _worker_loads: worker_loads,
             _load_monitor_handle: load_monitor_handle,
@@ -162,9 +164,11 @@ impl Router {
         model_id: Option<&str>,
         text: Option<&str>,
     ) -> Option<Arc<dyn Worker>> {
+        let effective_model_id = if !self.enable_igw { None } else { model_id };
+
         // Get workers for the specified model O(1), filtered by connection mode
         let workers = self.worker_registry.get_workers_filtered(
-            model_id,
+            effective_model_id,
             Some(WorkerType::Regular),
             Some(ConnectionMode::Http),
             false, // get all workers, we'll filter by is_available() next
@@ -1106,6 +1110,7 @@ mod tests {
             retry_config: RetryConfig::default(),
             _worker_loads: Arc::new(rx),
             _load_monitor_handle: None,
+            enable_igw: false,
         }
     }