feat(runtime): add DYN_TCP_RESPONSE_STREAM_PORT/HOST env vars for configurable...

feat(runtime): add DYN_TCP_RESPONSE_STREAM_PORT/HOST env vars for configurable response stream server port

lib/runtime/src/config/environment_names.rs

@@ -14,6 +14,7 @@
 //! - **Runtime**: Tokio runtime configuration and system server settings
 //! - **NATS**: NATS client connection and authentication
 //! - **ETCD**: ETCD client connection and authentication
+//! - **TCP Response Stream**: TCP response stream server (CallHome) port and host
 //! - **Event Plane**: Event transport selection (NATS)
 //! - **KVBM**: Key-Value Block Manager configuration
 //! - **LLM**: Language model inference configuration
@@ -351,6 +352,17 @@ pub mod router {
     pub const DYN_ROUTER_QUEUE_POLICY: &str = "DYN_ROUTER_QUEUE_POLICY";
 }
 
+/// TCP response stream server (CallHome listener) environment variables
+pub mod tcp_response_stream {
+    /// Port for the TCP response stream server.
+    /// If unset or 0, the OS assigns a free ephemeral port.
+    pub const DYN_TCP_RESPONSE_STREAM_PORT: &str = "DYN_TCP_RESPONSE_STREAM_PORT";
+
+    /// Host/interface for the TCP response stream server.
+    /// If unset, the server auto-detects a routable local IP.
+    pub const DYN_TCP_RESPONSE_STREAM_HOST: &str = "DYN_TCP_RESPONSE_STREAM_HOST";
+}
+
 /// Event Plane transport environment variables
 pub mod event_plane {
     /// Event transport selection: "zmq" or "nats". Default: "nats"
@@ -505,6 +517,9 @@ mod tests {
             // Router
             router::DYN_ROUTER_QUEUE_THRESHOLD,
             router::DYN_ROUTER_QUEUE_POLICY,
+            // TCP Response Stream
+            tcp_response_stream::DYN_TCP_RESPONSE_STREAM_PORT,
+            tcp_response_stream::DYN_TCP_RESPONSE_STREAM_HOST,
             // Event Plane
             event_plane::DYN_EVENT_PLANE,
             event_plane::DYN_EVENT_PLANE_CODEC,

lib/runtime/src/distributed.rs

@@ -4,6 +4,7 @@
 use crate::component::{
     self, Component, ComponentBuilder, Endpoint, Instance, Namespace, RoutingOccupancyState,
 };
+use crate::config::environment_names::tcp_response_stream;
 use crate::pipeline::PipelineError;
 use crate::pipeline::network::manager::NetworkManager;
 use crate::service::{ServiceClient, ServiceSet};
@@ -344,7 +345,34 @@ impl DistributedRuntime {
         Ok(self
             .tcp_server
             .get_or_try_init(async move {
-                let options = tcp::server::ServerOptions::default();
+                let port = match std::env::var(tcp_response_stream::DYN_TCP_RESPONSE_STREAM_PORT) {
+                    Ok(p) => p.parse::<u16>().map_err(|_| {
+                        PipelineError::Generic(format!(
+                            "invalid {}: '{}' is not a valid port number",
+                            tcp_response_stream::DYN_TCP_RESPONSE_STREAM_PORT,
+                            p
+                        ))
+                    })?,
+                    Err(_) => 0,
+                };
+                let interface = std::env::var(tcp_response_stream::DYN_TCP_RESPONSE_STREAM_HOST)
+                    .ok()
+                    .filter(|h| !h.is_empty());
+
+                let host_suffix = interface
+                    .as_ref()
+                    .map_or(String::new(), |h| format!(" on host {h}"));
+                if port == 0 {
+                    tracing::info!(
+                        "TCP response stream server using OS-assigned port{host_suffix}"
+                    );
+                } else {
+                    tracing::info!(
+                        "TCP response stream server using fixed port {port}{host_suffix}"
+                    );
+                }
+
+                let options = tcp::server::ServerOptions { port, interface };
                 let server = tcp::server::TcpStreamServer::new(options).await?;
                 Ok::<_, PipelineError>(server)
             })