diff --git a/rust/crates/runtime/src/lib.rs b/rust/crates/runtime/src/lib.rs
index 62e78d8..75c1b9f 100644
--- a/rust/crates/runtime/src/lib.rs
+++ b/rust/crates/runtime/src/lib.rs
@@ -16,6 +16,7 @@ mod remote;
 pub mod sandbox;
 mod session;
 mod sse;
+pub mod task_registry;
 mod usage;
 
 pub use bash::{execute_bash, BashCommandInput, BashCommandOutput};
diff --git a/rust/crates/runtime/src/task_registry.rs b/rust/crates/runtime/src/task_registry.rs
new file mode 100644
index 0000000..861f9bc
--- /dev/null
+++ b/rust/crates/runtime/src/task_registry.rs
@@ -0,0 +1,335 @@
+//! In-memory task registry for sub-agent task lifecycle management.
+//!
+//! Provides create, get, list, stop, update, and output operations
+//! matching the upstream TaskCreate/TaskGet/TaskList/TaskStop/TaskUpdate/TaskOutput
+//! tool surface.
+
+use std::collections::HashMap;
+use std::sync::{Arc, Mutex};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use serde::{Deserialize, Serialize};
+
+/// Current status of a managed task.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum TaskStatus {
+    Created,
+    Running,
+    Completed,
+    Failed,
+    Stopped,
+}
+
+impl std::fmt::Display for TaskStatus {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Created => write!(f, "created"),
+            Self::Running => write!(f, "running"),
+            Self::Completed => write!(f, "completed"),
+            Self::Failed => write!(f, "failed"),
+            Self::Stopped => write!(f, "stopped"),
+        }
+    }
+}
+
+/// A single managed task entry.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Task {
+    pub task_id: String,
+    pub prompt: String,
+    pub description: Option<String>,
+    pub status: TaskStatus,
+    pub created_at: u64,
+    pub updated_at: u64,
+    pub messages: Vec<TaskMessage>,
+    pub output: String,
+    pub team_id: Option<String>,
+}
+
+/// A message exchanged with a running task.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TaskMessage {
+    pub role: String,
+    pub content: String,
+    pub timestamp: u64,
+}
+
+/// Thread-safe task registry.
+#[derive(Debug, Clone, Default)]
+pub struct TaskRegistry {
+    inner: Arc<Mutex<RegistryInner>>,
+}
+
+#[derive(Debug, Default)]
+struct RegistryInner {
+    tasks: HashMap<String, Task>,
+    counter: u64,
+}
+
+fn now_secs() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs()
+}
+
+impl TaskRegistry {
+    /// Create a new empty registry.
+    #[must_use]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Create a new task and return its ID.
+    pub fn create(&self, prompt: &str, description: Option<&str>) -> Task {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        inner.counter += 1;
+        let ts = now_secs();
+        let task_id = format!("task_{:08x}_{}", ts, inner.counter);
+        let task = Task {
+            task_id: task_id.clone(),
+            prompt: prompt.to_owned(),
+            description: description.map(str::to_owned),
+            status: TaskStatus::Created,
+            created_at: ts,
+            updated_at: ts,
+            messages: Vec::new(),
+            output: String::new(),
+            team_id: None,
+        };
+        inner.tasks.insert(task_id, task.clone());
+        task
+    }
+
+    /// Look up a task by ID.
+    pub fn get(&self, task_id: &str) -> Option<Task> {
+        let inner = self.inner.lock().expect("registry lock poisoned");
+        inner.tasks.get(task_id).cloned()
+    }
+
+    /// List all tasks, optionally filtered by status.
+    pub fn list(&self, status_filter: Option<TaskStatus>) -> Vec<Task> {
+        let inner = self.inner.lock().expect("registry lock poisoned");
+        inner
+            .tasks
+            .values()
+            .filter(|t| status_filter.map_or(true, |s| t.status == s))
+            .cloned()
+            .collect()
+    }
+
+    /// Mark a task as stopped.
+    pub fn stop(&self, task_id: &str) -> Result<Task, String> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get_mut(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+
+        match task.status {
+            TaskStatus::Completed | TaskStatus::Failed | TaskStatus::Stopped => {
+                return Err(format!(
+                    "task {task_id} is already in terminal state: {}",
+                    task.status
+                ));
+            }
+            _ => {}
+        }
+
+        task.status = TaskStatus::Stopped;
+        task.updated_at = now_secs();
+        Ok(task.clone())
+    }
+
+    /// Send a message to a task, updating its state.
+    pub fn update(&self, task_id: &str, message: &str) -> Result<Task, String> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get_mut(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+
+        task.messages.push(TaskMessage {
+            role: String::from("user"),
+            content: message.to_owned(),
+            timestamp: now_secs(),
+        });
+        task.updated_at = now_secs();
+        Ok(task.clone())
+    }
+
+    /// Get the accumulated output of a task.
+    pub fn output(&self, task_id: &str) -> Result<String, String> {
+        let inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+        Ok(task.output.clone())
+    }
+
+    /// Append output to a task (used by the task executor).
+    pub fn append_output(&self, task_id: &str, output: &str) -> Result<(), String> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get_mut(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+        task.output.push_str(output);
+        task.updated_at = now_secs();
+        Ok(())
+    }
+
+    /// Transition a task to a new status.
+    pub fn set_status(&self, task_id: &str, status: TaskStatus) -> Result<(), String> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get_mut(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+        task.status = status;
+        task.updated_at = now_secs();
+        Ok(())
+    }
+
+    /// Assign a task to a team.
+    pub fn assign_team(&self, task_id: &str, team_id: &str) -> Result<(), String> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        let task = inner
+            .tasks
+            .get_mut(task_id)
+            .ok_or_else(|| format!("task not found: {task_id}"))?;
+        task.team_id = Some(team_id.to_owned());
+        task.updated_at = now_secs();
+        Ok(())
+    }
+
+    /// Remove a task from the registry.
+    pub fn remove(&self, task_id: &str) -> Option<Task> {
+        let mut inner = self.inner.lock().expect("registry lock poisoned");
+        inner.tasks.remove(task_id)
+    }
+
+    /// Number of tasks in the registry.
+    #[must_use]
+    pub fn len(&self) -> usize {
+        let inner = self.inner.lock().expect("registry lock poisoned");
+        inner.tasks.len()
+    }
+
+    /// Whether the registry has no tasks.
+    #[must_use]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn creates_and_retrieves_tasks() {
+        let registry = TaskRegistry::new();
+        let task = registry.create("Do something", Some("A test task"));
+        assert_eq!(task.status, TaskStatus::Created);
+        assert_eq!(task.prompt, "Do something");
+        assert_eq!(task.description.as_deref(), Some("A test task"));
+
+        let fetched = registry.get(&task.task_id).expect("task should exist");
+        assert_eq!(fetched.task_id, task.task_id);
+    }
+
+    #[test]
+    fn lists_tasks_with_optional_filter() {
+        let registry = TaskRegistry::new();
+        registry.create("Task A", None);
+        let task_b = registry.create("Task B", None);
+        registry
+            .set_status(&task_b.task_id, TaskStatus::Running)
+            .expect("set status should succeed");
+
+        let all = registry.list(None);
+        assert_eq!(all.len(), 2);
+
+        let running = registry.list(Some(TaskStatus::Running));
+        assert_eq!(running.len(), 1);
+        assert_eq!(running[0].task_id, task_b.task_id);
+
+        let created = registry.list(Some(TaskStatus::Created));
+        assert_eq!(created.len(), 1);
+    }
+
+    #[test]
+    fn stops_running_task() {
+        let registry = TaskRegistry::new();
+        let task = registry.create("Stoppable", None);
+        registry
+            .set_status(&task.task_id, TaskStatus::Running)
+            .unwrap();
+
+        let stopped = registry.stop(&task.task_id).expect("stop should succeed");
+        assert_eq!(stopped.status, TaskStatus::Stopped);
+
+        // Stopping again should fail
+        let result = registry.stop(&task.task_id);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn updates_task_with_messages() {
+        let registry = TaskRegistry::new();
+        let task = registry.create("Messageable", None);
+        let updated = registry
+            .update(&task.task_id, "Here's more context")
+            .expect("update should succeed");
+        assert_eq!(updated.messages.len(), 1);
+        assert_eq!(updated.messages[0].content, "Here's more context");
+        assert_eq!(updated.messages[0].role, "user");
+    }
+
+    #[test]
+    fn appends_and_retrieves_output() {
+        let registry = TaskRegistry::new();
+        let task = registry.create("Output task", None);
+        registry
+            .append_output(&task.task_id, "line 1\n")
+            .expect("append should succeed");
+        registry
+            .append_output(&task.task_id, "line 2\n")
+            .expect("append should succeed");
+
+        let output = registry.output(&task.task_id).expect("output should exist");
+        assert_eq!(output, "line 1\nline 2\n");
+    }
+
+    #[test]
+    fn assigns_team_and_removes_task() {
+        let registry = TaskRegistry::new();
+        let task = registry.create("Team task", None);
+        registry
+            .assign_team(&task.task_id, "team_abc")
+            .expect("assign should succeed");
+
+        let fetched = registry.get(&task.task_id).unwrap();
+        assert_eq!(fetched.team_id.as_deref(), Some("team_abc"));
+
+        let removed = registry.remove(&task.task_id);
+        assert!(removed.is_some());
+        assert!(registry.get(&task.task_id).is_none());
+        assert!(registry.is_empty());
+    }
+
+    #[test]
+    fn rejects_operations_on_missing_task() {
+        let registry = TaskRegistry::new();
+        assert!(registry.stop("nonexistent").is_err());
+        assert!(registry.update("nonexistent", "msg").is_err());
+        assert!(registry.output("nonexistent").is_err());
+        assert!(registry.append_output("nonexistent", "data").is_err());
+        assert!(registry
+            .set_status("nonexistent", TaskStatus::Running)
+            .is_err());
+    }
+}