feat: enable Streamable HTTP MCP servers & lazy loading of tools

codex-rs/config.md

@@ -3,4 +3,4 @@
 This file has moved. Please see the latest configuration documentation here:
 
 - Full config docs: [docs/config.md](../docs/config.md)
-- MCP servers section: [docs/config.md#mcp_servers](../docs/config.md#mcp_servers) 
+- MCP servers section: [docs/config.md#mcp_servers](../docs/config.md#mcp_servers)

codex-rs/core/src/codex.rs

@@ -576,6 +576,9 @@ impl Session {
             }
         }
 
+        // Kick off background MCP tool initialization/loading without blocking the UI.
+        sess.mcp_connection_manager.refresh_tools_in_background();
+
         Ok((sess, turn_context))
     }
 
@@ -1286,7 +1289,12 @@ async fn submission_loop(
                 let tx_event = sess.tx_event.clone();
                 let sub_id = sub.id.clone();
 
-                // This is a cheap lookup from the connection manager's cache.
+                // Refresh tools on-demand to give users an up-to-date list.
+                // This runs in the foreground for this operation only.
+                if let Err(e) = sess.mcp_connection_manager.refresh_tools().await {
+                    warn!("failed to refresh MCP tools: {e:#}");
+                }
+
                 let tools = sess.mcp_connection_manager.list_all_tools();
                 let event = Event {
                     id: sub_id,
@@ -1613,6 +1621,12 @@ async fn run_turn(
     sub_id: String,
     input: Vec<ResponseItem>,
 ) -> CodexResult<Vec<ProcessedResponseItem>> {
+    // Give MCP tools a brief moment to arrive if background discovery is still running.
+    // This avoids an empty tool list in the first turn right after startup.
+    sess.mcp_connection_manager
+        .wait_for_tools_with_timeout(std::time::Duration::from_millis(800))
+        .await;
+
     let tools = get_openai_tools(
         &turn_context.tools_config,
         Some(sess.mcp_connection_manager.list_all_tools()),

codex-rs/core/src/config_types.rs

@@ -12,14 +12,25 @@ use serde::Serialize;
 use strum_macros::Display;
 
 #[derive(Deserialize, Debug, Clone, PartialEq)]
-pub struct McpServerConfig {
-    pub command: String,
-
-    #[serde(default)]
-    pub args: Vec<String>,
-
-    #[serde(default)]
-    pub env: Option<HashMap<String, String>>,
+#[serde(untagged)]
+pub enum McpServerConfig {
+    /// MCP server launched as a subprocess that communicates over stdio.
+    Stdio {
+        command: String,
+
+        #[serde(default)]
+        args: Vec<String>,
+
+        #[serde(default)]
+        env: Option<HashMap<String, String>>,
+    },
+    /// MCP server reachable via the Streamable HTTP transport.
+    StreamableHttp {
+        url: String,
+
+        #[serde(default)]
+        headers: Option<HashMap<String, String>>,
+    },
 }
 
 #[derive(Deserialize, Debug, Copy, Clone, PartialEq)]