feat: implement background agents and async messaging system

This commit adds the complete background worker architecture and asynchronous
messaging system for the CLI as specified in ORCHESTRATE/AGENT_1_BACKGROUND_AGENTS.md.

## New Features

### Background Agent Module (cortex-agents/src/background/)
- **executor.rs**: BackgroundAgentManager for spawning and managing background tasks
  - Configurable max concurrent agents (default: 5)
  - Automatic timeout after 30 minutes
  - RAII cleanup with proper cancellation support
  - Event broadcasting for monitoring

- **messaging.rs**: Inter-agent async messaging system
  - AgentMailbox for per-agent message queues
  - MessageRouter for routing messages between agents
  - Support for notifications, requests/responses, data sharing, and status updates

- **events.rs**: Event system for background agents
  - AgentEvent enum for lifecycle events (Started, Progress, Completed, Failed, Cancelled)
  - NotificationManager for collecting and displaying notifications
  - Support for TodoUpdated events for progress tracking

### TUI Enhancements (cortex-tui/)
- New /tasks command (aliases: /bg, /background) for viewing background tasks
- TasksView component for displaying task status, duration, and progress
- ModalType::Tasks for the background tasks modal

## Tests
- 21 new unit tests covering:
  - Background agent spawning and cancellation
  - Max concurrent agent limits
  - Event subscription and notification
  - Inter-agent messaging
  - Notification management

## Implementation Details
- Uses tokio for async runtime with mpsc/broadcast channels
- Proper error handling with BackgroundAgentError enum
- Isolated agent contexts (no shared credentials)
- Grace period for cancellation (5 seconds)

Author: factorydroid

cortex-agents/src/background/events.rs

@@ -0,0 +1,63 @@
+//! Background agent execution system.
+//!
+//! This module provides infrastructure for running agents in the background
+//! with async communication, event broadcasting, and lifecycle management.
+//!
+//! # Architecture
+//!
+//! ```text
+//! BackgroundAgentManager
+//!     ├── BackgroundAgent (tokio task)
+//!     │   ├── status channel (mpsc)
+//!     │   ├── cancel channel (oneshot)
+//!     │   └── mailbox (AgentMailbox)
+//!     ├── Event broadcaster (broadcast)
+//!     └── Agent registry (HashMap)
+//! ```
+//!
+//! # Example
+//!
+//! ```rust,ignore
+//! use cortex_agents::background::{
+//!     BackgroundAgentManager, AgentConfig, AgentEvent
+//! };
+//!
+//! // Create manager
+//! let mut manager = BackgroundAgentManager::new(5);
+//!
+//! // Subscribe to events
+//! let mut events = manager.subscribe();
+//!
+//! // Spawn a background agent
+//! let id = manager.spawn(AgentConfig::new("Search for patterns")).await?;
+//!
+//! // Monitor events
+//! while let Ok(event) = events.recv().await {
+//!     match event {
+//!         AgentEvent::Progress { id, message } => println!("{}: {}", id, message),
+//!         AgentEvent::Completed { id, result } => {
+//!             println!("Agent {} completed: {:?}", id, result);
+//!             break;
+//!         }
+//!         _ => {}
+//!     }
+//! }
+//! ```
+//!
+//! # Safety & Limits
+//!
+//! - Maximum concurrent agents: configurable (default 5)
+//! - Automatic timeout: 30 minutes per agent
+//! - RAII cleanup: agents are cancelled when manager is dropped
+//! - Isolated contexts: agents don't share credentials
+
+pub mod events;
+pub mod executor;
+pub mod messaging;
+
+pub use events::{AgentEvent, Notification, NotificationLevel, NotificationManager};
+pub use executor::{
+    AgentConfig, AgentResult, AgentStatus, BackgroundAgent, BackgroundAgentError,
+    BackgroundAgentManager,
+};
+pub use messaging::{AgentMailbox, AgentMessage, MessageContent, MessageRouter};

cortex-agents/src/background/executor.rs

@@ -112,7 +112,37 @@
 //! let decision = decide_routing(&tasks);
 //! assert_eq!(decision.mode, DispatchMode::Parallel);
 //! ```
+//!
+//! # Background Agents
+//!
+//! The background module provides infrastructure for running agents as background
+//! tokio tasks with async messaging:
+//!
+//! ```rust,ignore
+//! use cortex_agents::background::{BackgroundAgentManager, AgentConfig, AgentEvent};
+//!
+//! // Create manager
+//! let mut manager = BackgroundAgentManager::new(5);
+//!
+//! // Subscribe to events
+//! let mut events = manager.subscribe();
+//!
+//! // Spawn a background agent
+//! let id = manager.spawn(AgentConfig::new("Search for patterns")).await?;
+//!
+//! // Monitor events
+//! while let Ok(event) = events.recv().await {
+//!     match event {
+//!         AgentEvent::Completed { id, summary, .. } => {
+//!             println!("Agent {} completed: {}", id, summary);
+//!             break;
+//!         }
+//!         _ => {}
+//!     }
+//! }
+//! ```
 
+pub mod background;
 pub mod collab;
 pub mod control;
 pub mod custom;
@@ -176,6 +206,13 @@ pub use routing::{
     can_parallelize, decide_routing, estimate_duration, DispatchMode, RoutingDecision, TaskInfo,
 };
 
+// Re-export background agent types
+pub use background::{
+    AgentConfig, AgentEvent, AgentMailbox, AgentMessage, AgentResult, AgentStatus, BackgroundAgent,
+    BackgroundAgentError, BackgroundAgentManager, MessageContent, MessageRouter, Notification,
+    NotificationLevel, NotificationManager,
+};
+
 use thiserror::Error;
 
 #[derive(Error, Debug)]

cortex-agents/src/background/messaging.rs

@@ -83,6 +83,7 @@ impl CommandExecutor {
             "init" => self.cmd_init(cmd),
             "commands" | "cmds" => CommandResult::Async("commands:list".to_string()),
             "agents" | "subagents" => CommandResult::OpenModal(ModalType::Agents),
+            "tasks" | "bg" | "background" => CommandResult::OpenModal(ModalType::Tasks),
             "copy" | "cp" => CommandResult::Message(
                 "To copy text from Cortex:\n\n\
                  - Hold SHIFT while selecting text with mouse\n\

cortex-agents/src/background/mod.rs

@@ -279,6 +279,15 @@ pub fn register_builtin_commands(registry: &mut CommandRegistry) {
         false,
     ));
 
+    registry.register(CommandDef::new(
+        "tasks",
+        &["bg", "background"],
+        "View and manage background tasks",
+        "/tasks",
+        CommandCategory::General,
+        false,
+    ));
+
     registry.register(CommandDef::new(
         "share",
         &[],

cortex-agents/src/lib.rs

@@ -156,6 +156,8 @@ pub enum ModalType {
     Upgrade,
     /// Agents manager modal for listing and creating agents
     Agents,
+    /// Background tasks view modal
+    Tasks,
 }
 
 impl ModalType {
@@ -181,6 +183,7 @@ impl ModalType {
             ModalType::Login => "Login",
             ModalType::Upgrade => "Upgrade",
             ModalType::Agents => "Agents",
+            ModalType::Tasks => "Background Tasks",
         }
     }
 }

cortex-tui/src/commands/executor.rs

@@ -7,14 +7,17 @@
 //! - [`MinimalSessionView`](minimal_session::MinimalSessionView) - Minimalist terminal-style chat
 //! - [`ApprovalView`](approval::ApprovalView) - Tool approval modal
 //! - [`QuestionPromptView`](question_prompt::QuestionPromptView) - Interactive question prompt
+//! - [`TasksView`](tasks::TasksView) - Background tasks monitoring view
 //! - [`tool_call`] - Tool call display types
 
 pub mod approval;
 pub mod minimal_session;
 pub mod question_prompt;
+pub mod tasks;
 pub mod tool_call;
 
 // Re-exports
 pub use approval::ApprovalView;
 pub use minimal_session::MinimalSessionView;
 pub use question_prompt::{QuestionClickZones, QuestionHit, QuestionPromptView};
+pub use tasks::{TaskDisplay, TaskStatus, TasksView};