diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 3cb3277531..7d77445eba 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -522,15 +522,14 @@ impl Session {
         let mut subagents_registry =
             crate::subagents::registry::SubagentRegistry::new(project_agents_dir, user_agents_dir);
         subagents_registry.load();
-        // Log discovered subagents for visibility in clients (e.g., TUI).
-        let _ = tx_event
-            .send(Event {
-                id: INITIAL_SUBMIT_ID.to_string(),
-                msg: EventMsg::BackgroundEvent(BackgroundEventEvent {
-                    message: format!("subagents discovered: {:?}", subagents_registry.all_names()),
-                }),
-            })
-            .await;
+        // Log discovered subagents for visibility in clients (e.g., TUI) after
+        // SessionConfigured so the first event contract remains intact.
+        post_session_configured_error_events.push(Event {
+            id: INITIAL_SUBMIT_ID.to_string(),
+            msg: EventMsg::BackgroundEvent(BackgroundEventEvent {
+                message: format!("subagents discovered: {:?}", subagents_registry.all_names()),
+            }),
+        });
 
         let turn_context = TurnContext {
             client,
@@ -1604,6 +1603,7 @@ async fn run_turn(
         &turn_context.tools_config,
         Some(sess.mcp_connection_manager.list_all_tools()),
     );
+    tracing::trace!("Tools: {tools:?}");
 
     // Log tool names for visibility in the TUI/debug logs.
     #[allow(clippy::match_same_arms)]
@@ -2143,7 +2143,7 @@ async fn handle_function_call(
             .await
         }
         "update_plan" => handle_update_plan(sess, arguments, sub_id, call_id).await,
-        "subagent.run" => {
+        "subagent_run" => {
             #[derive(serde::Deserialize)]
             struct Args {
                 name: String,
@@ -2194,6 +2194,33 @@ async fn handle_function_call(
                 },
             }
         }
+        "subagent_list" => {
+            #[derive(serde::Serialize)]
+            struct SubagentBrief<'a> {
+                name: &'a str,
+                description: &'a str,
+            }
+            let mut list = Vec::new();
+            for name in sess.subagents_registry.all_names() {
+                if let Some(def) = sess.subagents_registry.get(&name) {
+                    list.push(SubagentBrief {
+                        name: &def.name,
+                        description: &def.description,
+                    });
+                }
+            }
+            let payload = match serde_json::to_string(&list) {
+                Ok(s) => s,
+                Err(e) => format!("failed to serialize subagent list: {e}"),
+            };
+            ResponseInputItem::FunctionCallOutput {
+                call_id,
+                output: FunctionCallOutputPayload {
+                    content: payload,
+                    success: Some(true),
+                },
+            }
+        }
         _ => {
             match sess.mcp_connection_manager.parse_tool_name(&name) {
                 Some((server, tool_name)) => {
diff --git a/codex-rs/core/src/openai_tools.rs b/codex-rs/core/src/openai_tools.rs
index ad2543f618..c8a45935de 100644
--- a/codex-rs/core/src/openai_tools.rs
+++ b/codex-rs/core/src/openai_tools.rs
@@ -515,6 +515,7 @@ pub(crate) fn get_openai_tools(
     if config.subagent_tool {
         tracing::trace!("Adding subagent tool");
         tools.push(crate::subagents::SUBAGENT_TOOL.clone());
+        tools.push(crate::subagents::SUBAGENT_LIST_TOOL.clone());
     }
 
     if let Some(mcp_tools) = mcp_tools {
diff --git a/codex-rs/core/src/subagents/definition.rs b/codex-rs/core/src/subagents/definition.rs
new file mode 100644
index 0000000000..f7f7d2384b
--- /dev/null
+++ b/codex-rs/core/src/subagents/definition.rs
@@ -0,0 +1,32 @@
+use serde::Deserialize;
+use std::fs;
+use std::path::Path;
+
+#[derive(Debug, Clone, Deserialize)]
+pub struct SubagentDefinition {
+    pub name: String,
+    pub description: String,
+    /// Base instructions for this subagent.
+    pub instructions: String,
+    /// When not set, inherits the parent agent's tool set. When set to an
+    /// empty list, no tools are available to the subagent.
+    #[serde(default)]
+    pub tools: Option<Vec<String>>, // None => inherit; Some(vec) => allow-list
+}
+
+impl SubagentDefinition {
+    pub fn from_json_str(s: &str) -> Result<Self, serde_json::Error> {
+        serde_json::from_str::<Self>(s)
+    }
+
+    pub fn from_file(path: &Path) -> std::io::Result<Self> {
+        let contents = fs::read_to_string(path)?;
+        // Surface JSON parsing error with file context
+        serde_json::from_str::<Self>(&contents).map_err(|e| {
+            std::io::Error::new(
+                std::io::ErrorKind::InvalidData,
+                format!("invalid subagent JSON at {}: {e}", path.display()),
+            )
+        })
+    }
+}
diff --git a/codex-rs/core/src/subagents/mod.rs b/codex-rs/core/src/subagents/mod.rs
new file mode 100644
index 0000000000..765da8fd2d
--- /dev/null
+++ b/codex-rs/core/src/subagents/mod.rs
@@ -0,0 +1,6 @@
+pub mod definition;
+pub mod registry;
+pub mod runner;
+pub mod tool;
+
+pub(crate) use tool::{SUBAGENT_LIST_TOOL, SUBAGENT_TOOL};
diff --git a/codex-rs/core/src/subagents/registry.rs b/codex-rs/core/src/subagents/registry.rs
new file mode 100644
index 0000000000..b253652494
--- /dev/null
+++ b/codex-rs/core/src/subagents/registry.rs
@@ -0,0 +1,92 @@
+use super::definition::SubagentDefinition;
+use std::collections::HashMap;
+use std::fs;
+use std::path::Path;
+use std::path::PathBuf;
+
+#[derive(Debug, Default, Clone)]
+pub struct SubagentRegistry {
+    /// Directory under the project (cwd/.codex/agents).
+    project_dir: Option<PathBuf>,
+    /// Directory under CODEX_HOME (~/.codex/agents).
+    user_dir: Option<PathBuf>,
+    /// Merged map: project definitions override user ones.
+    map: HashMap<String, SubagentDefinition>,
+}
+
+impl SubagentRegistry {
+    pub fn new(project_dir: Option<PathBuf>, user_dir: Option<PathBuf>) -> Self {
+        Self {
+            project_dir,
+            user_dir,
+            map: HashMap::new(),
+        }
+    }
+
+    /// Loads JSON files from user_dir then project_dir (project wins on conflict).
+    pub fn load(&mut self) {
+        let mut map: HashMap<String, SubagentDefinition> = HashMap::new();
+
+        // Load user definitions first
+        if let Some(dir) = &self.user_dir {
+            Self::load_from_dir_into(dir, &mut map);
+        }
+        // Then load project definitions which override on conflicts
+        if let Some(dir) = &self.project_dir {
+            Self::load_from_dir_into(dir, &mut map);
+        }
+
+        // Ensure a simple built‑in test subagent exists to validate wiring end‑to‑end.
+        // Users can override this by providing their own definition named "hello".
+        if !map.contains_key("hello") {
+            map.insert(
+                "hello".to_string(),
+                SubagentDefinition {
+                    name: "hello".to_string(),
+                    description: "Built‑in test subagent that replies with a greeting".to_string(),
+                    // Keep instructions narrow so models reliably output the intended text.
+                    instructions:
+                        "Reply with exactly this text and nothing else: Hello from subagent"
+                            .to_string(),
+                    // Disallow tool usage for the hello subagent.
+                    tools: Some(Vec::new()),
+                },
+            );
+        }
+
+        self.map = map;
+    }
+
+    pub fn get(&self, name: &str) -> Option<&SubagentDefinition> {
+        self.map.get(name)
+    }
+
+    pub fn all_names(&self) -> Vec<String> {
+        self.map.keys().cloned().collect()
+    }
+
+    fn load_from_dir_into(dir: &Path, out: &mut HashMap<String, SubagentDefinition>) {
+        let Ok(iter) = fs::read_dir(dir) else {
+            return;
+        };
+        for entry in iter.flatten() {
+            let path = entry.path();
+            if path.is_file()
+                && path
+                    .extension()
+                    .and_then(|e| e.to_str())
+                    .map(|e| e.eq_ignore_ascii_case("json"))
+                    .unwrap_or(false)
+            {
+                match SubagentDefinition::from_file(&path) {
+                    Ok(def) => {
+                        out.insert(def.name.clone(), def);
+                    }
+                    Err(e) => {
+                        tracing::warn!("Failed to load subagent from {}: {}", path.display(), e);
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/codex-rs/core/src/subagents/runner.rs b/codex-rs/core/src/subagents/runner.rs
new file mode 100644
index 0000000000..366aa64830
--- /dev/null
+++ b/codex-rs/core/src/subagents/runner.rs
@@ -0,0 +1,142 @@
+use crate::codex::Codex;
+use crate::error::Result as CodexResult;
+
+use super::definition::SubagentDefinition;
+use super::registry::SubagentRegistry;
+
+/// Arguments expected for the `subagent.run` tool.
+#[derive(serde::Deserialize)]
+pub struct RunSubagentArgs {
+    pub name: String,
+    pub input: String,
+    #[serde(default)]
+    pub context: Option<String>,
+}
+
+/// Run a subagent in a nested Codex session and return the final message.
+pub(crate) async fn run(
+    sess: &crate::codex::Session,
+    turn_context: &crate::codex::TurnContext,
+    registry: &SubagentRegistry,
+    args: RunSubagentArgs,
+    _parent_sub_id: &str,
+) -> CodexResult<String> {
+    let def: &SubagentDefinition = registry.get(&args.name).ok_or_else(|| {
+        crate::error::CodexErr::Stream(format!("unknown subagent: {}", args.name), None)
+    })?;
+
+    let mut nested_cfg = (*sess.base_config()).clone();
+    nested_cfg.base_instructions = Some(def.instructions.clone());
+    nested_cfg.user_instructions = None;
+    nested_cfg.approval_policy = turn_context.approval_policy;
+    nested_cfg.sandbox_policy = turn_context.sandbox_policy.clone();
+    nested_cfg.cwd = turn_context.cwd.clone();
+    nested_cfg.include_subagent_tool = false;
+
+    let nested = Codex::spawn(nested_cfg, sess.auth_manager(), None).await?;
+    let nested_codex = nested.codex;
+
+    let subagent_id = uuid::Uuid::new_v4().to_string();
+    forward_begin(sess, _parent_sub_id, &subagent_id, &def.name).await;
+
+    let text = match args.context {
+        Some(ctx) if !ctx.trim().is_empty() => format!("{ctx}\n\n{input}", input = args.input),
+        _ => args.input,
+    };
+
+    nested_codex
+        .submit(crate::protocol::Op::UserInput {
+            items: vec![crate::protocol::InputItem::Text { text }],
+        })
+        .await
+        .map_err(|e| {
+            crate::error::CodexErr::Stream(format!("failed to submit to subagent: {e}"), None)
+        })?;
+
+    let mut last_message: Option<String> = None;
+    loop {
+        let ev = nested_codex.next_event().await?;
+        match ev.msg.clone() {
+            crate::protocol::EventMsg::AgentMessage(m) => {
+                last_message = Some(m.message);
+            }
+            crate::protocol::EventMsg::TaskComplete(t) => {
+                let _ = nested_codex.submit(crate::protocol::Op::Shutdown).await;
+                forward_forwarded(sess, _parent_sub_id, &subagent_id, &def.name, ev.msg).await;
+                forward_end(
+                    sess,
+                    _parent_sub_id,
+                    &subagent_id,
+                    &def.name,
+                    true,
+                    t.last_agent_message.clone(),
+                )
+                .await;
+                return Ok(t
+                    .last_agent_message
+                    .unwrap_or_else(|| last_message.unwrap_or_default()));
+            }
+            _ => {}
+        }
+        forward_forwarded(sess, _parent_sub_id, &subagent_id, &def.name, ev.msg).await;
+    }
+}
+
+async fn forward_begin(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentBegin(crate::protocol::SubagentBeginEvent {
+                subagent_id: subagent_id.to_string(),
+                name: name.to_string(),
+            }),
+        })
+        .await;
+}
+
+async fn forward_forwarded(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+    msg: crate::protocol::EventMsg,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentForwarded(
+                crate::protocol::SubagentForwardedEvent {
+                    subagent_id: subagent_id.to_string(),
+                    name: name.to_string(),
+                    event: Box::new(msg),
+                },
+            ),
+        })
+        .await;
+}
+
+async fn forward_end(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+    success: bool,
+    last_agent_message: Option<String>,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentEnd(crate::protocol::SubagentEndEvent {
+                subagent_id: subagent_id.to_string(),
+                name: name.to_string(),
+                success,
+                last_agent_message,
+            }),
+        })
+        .await;
+}
diff --git a/codex-rs/core/src/subagents/tool.rs b/codex-rs/core/src/subagents/tool.rs
new file mode 100644
index 0000000000..7a7109fd3c
--- /dev/null
+++ b/codex-rs/core/src/subagents/tool.rs
@@ -0,0 +1,54 @@
+use std::collections::BTreeMap;
+use std::sync::LazyLock;
+
+use crate::openai_tools::JsonSchema;
+use crate::openai_tools::OpenAiTool;
+use crate::openai_tools::ResponsesApiTool;
+
+pub(crate) static SUBAGENT_TOOL: LazyLock<OpenAiTool> = LazyLock::new(|| {
+    let mut properties = BTreeMap::new();
+    properties.insert(
+        "name".to_string(),
+        JsonSchema::String {
+            description: Some("Registered subagent name".to_string()),
+        },
+    );
+    properties.insert(
+        "input".to_string(),
+        JsonSchema::String {
+            description: Some("Task or instruction for the subagent".to_string()),
+        },
+    );
+    properties.insert(
+        "context".to_string(),
+        JsonSchema::String {
+            description: Some("Optional extra context to aid the task".to_string()),
+        },
+    );
+
+    OpenAiTool::Function(ResponsesApiTool {
+        name: "subagent_run".to_string(),
+        description: "Invoke a named subagent with isolated context and return its result"
+            .to_string(),
+        strict: false,
+        parameters: JsonSchema::Object {
+            properties,
+            required: Some(vec!["name".to_string(), "input".to_string()]),
+            additional_properties: Some(false),
+        },
+    })
+});
+
+pub(crate) static SUBAGENT_LIST_TOOL: LazyLock<OpenAiTool> = LazyLock::new(|| {
+    let properties = BTreeMap::new();
+    OpenAiTool::Function(ResponsesApiTool {
+        name: "subagent_list".to_string(),
+        description: "List available subagents (name and description). Call before subagent_run if unsure.".to_string(),
+        strict: false,
+        parameters: JsonSchema::Object {
+            properties,
+            required: None,
+            additional_properties: Some(false),
+        },
+    })
+});
diff --git a/codex-rs/exec/src/lib.rs b/codex-rs/exec/src/lib.rs
index 6d2b6ccc5d..637fc10fcd 100644
--- a/codex-rs/exec/src/lib.rs
+++ b/codex-rs/exec/src/lib.rs
@@ -146,6 +146,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         model_provider,
         codex_linux_sandbox_exe,
         base_instructions: None,
+        include_subagent_tool: None,
         include_plan_tool: None,
         include_apply_patch_tool: None,
         disable_response_storage: oss.then_some(true),
@@ -216,13 +217,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
                         Ok(event) => {
                             debug!("Received event: {event:?}");
 
-                            let is_shutdown_complete = matches!(
-                                event.msg,
-                                EventMsg::ShutdownComplete
-                                    | EventMsg::SubagentBegin(_)
-                                    | EventMsg::SubagentForwarded(_)
-                                    | EventMsg::SubagentEnd(_)
-                            );
+                            let is_shutdown_complete = matches!(event.msg, EventMsg::ShutdownComplete);
                             if let Err(e) = tx.send(event) {
                                 error!("Error sending event: {e:?}");
                                 break;
diff --git a/codex-rs/mcp-server/src/codex_message_processor.rs b/codex-rs/mcp-server/src/codex_message_processor.rs
index 0bbf6ff849..48e632b039 100644
--- a/codex-rs/mcp-server/src/codex_message_processor.rs
+++ b/codex-rs/mcp-server/src/codex_message_processor.rs
@@ -736,6 +736,7 @@ fn derive_config_from_params(
         base_instructions,
         include_plan_tool,
         include_apply_patch_tool,
+        include_subagent_tool: None,
         disable_response_storage: None,
         show_raw_agent_reasoning: None,
     };
diff --git a/codex-rs/mcp-server/src/codex_tool_config.rs b/codex-rs/mcp-server/src/codex_tool_config.rs
index 5993c10faf..0513bb8eb2 100644
--- a/codex-rs/mcp-server/src/codex_tool_config.rs
+++ b/codex-rs/mcp-server/src/codex_tool_config.rs
@@ -161,6 +161,7 @@ impl CodexToolCallParam {
             base_instructions,
             include_plan_tool,
             include_apply_patch_tool: None,
+            include_subagent_tool: None,
             disable_response_storage: None,
             show_raw_agent_reasoning: None,
         };
diff --git a/codex-rs/tui/src/history_cell.rs b/codex-rs/tui/src/history_cell.rs
index 47a3833e59..57848b10a4 100644
--- a/codex-rs/tui/src/history_cell.rs
+++ b/codex-rs/tui/src/history_cell.rs
@@ -752,9 +752,7 @@ pub(crate) fn new_status_output(
 
 /// Simple one-line log entry (dim) to surface traces and diagnostics in the transcript.
 pub(crate) fn new_log_line(message: String) -> TranscriptOnlyHistoryCell {
-    let mut lines: Vec<Line<'static>> = Vec::new();
-    lines.push(Line::from(""));
-    lines.push(Line::from(message).dim());
+    let lines: Vec<Line<'static>> = vec![Line::from(""), Line::from(message).dim()];
     TranscriptOnlyHistoryCell { lines }
 }