feat(agent): delegate tool (#3073)

* feat: implement delegate tool for background agent management

- Add delegate tool with list/launch/status operations
- Validate agent names against available configs
- Run agents silently in background with output capture
- Store execution state in ~/.aws/amazonq/.subagents/
- Include PID monitoring for crash detection
- Require experimental flag enablement

* adds slash command

* addresses comments

* removes slash command

* annotates chronos with seconds

---------

Co-authored-by: abhraina-aws <[email protected]>

Author: dingfeli

crates/chat-cli/src/cli/chat/mod.rs

@@ -106,6 +106,7 @@ use tool_manager::{
     ToolManager,
     ToolManagerBuilder,
 };
+use tools::delegate::status_all_agents;
 use tools::gh_issue::GhIssueContext;
 use tools::{
     NATIVE_TOOLS,
@@ -199,6 +200,8 @@ pub const EXTRA_HELP: &str = color_print::cstr! {"
                     <black!>Change the keybind using: q settings chat.skimCommandKey x</black!>
 <em>Ctrl(^) + t</em>         <black!>Toggle tangent mode for isolated conversations</black!>
                     <black!>Change the keybind using: q settings chat.tangentModeKey x</black!>
+<em>Ctrl(^) + d</em>         <black!>Start delegate command for task delegation</black!>
+                    <black!>Change the keybind using: q settings chat.delegateModeKey x</black!>
 <em>chat.editMode</em>       <black!>The prompt editing mode (vim or emacs)</black!>
                     <black!>Change using: q settings chat.skimCommandKey x</black!>
 "};
@@ -522,6 +525,7 @@ const CONTINUATION_LINE: &str = " ⋮ ";
 const PURPOSE_ARROW: &str = " ↳ ";
 const SUCCESS_TICK: &str = " ✓ ";
 const ERROR_EXCLAMATION: &str = " ❗ ";
+const DELEGATE_NOTIFIER: &str = "[BACKGROUND TASK READY]";
 
 /// Enum used to denote the origin of a tool use event
 enum ToolUseStatus {
@@ -2347,7 +2351,7 @@ impl ChatSession {
                     os,
                     &mut self.stdout,
                     &mut self.conversation.file_line_tracker,
-                    self.conversation.agents.get_active(),
+                    &self.conversation.agents,
                 )
                 .await;
 
@@ -3374,7 +3378,14 @@ impl ChatSession {
             None
         };
 
-        prompt::generate_prompt(profile.as_deref(), all_trusted, tangent_mode, usage_percentage)
+        let mut generated_prompt =
+            prompt::generate_prompt(profile.as_deref(), all_trusted, tangent_mode, usage_percentage);
+
+        if ExperimentManager::is_enabled(os, ExperimentName::Delegate) && status_all_agents(os).await.is_ok() {
+            generated_prompt = format!("{DELEGATE_NOTIFIER}\n{generated_prompt}");
+        }
+
+        generated_prompt
     }
 
     async fn send_tool_use_telemetry(&mut self, os: &Os) {

crates/chat-cli/src/cli/chat/prompt.rs

@@ -46,7 +46,10 @@ use super::tool_manager::{
     PromptQuery,
     PromptQueryResult,
 };
-use crate::cli::experiment::experiment_manager::ExperimentManager;
+use crate::cli::experiment::experiment_manager::{
+    ExperimentManager,
+    ExperimentName,
+};
 use crate::database::settings::Setting;
 use crate::os::Os;
 use crate::util::directories::chat_cli_bash_history_path;
@@ -417,6 +420,11 @@ impl Highlighter for ChatHelper {
         if let Some(components) = parse_prompt_components(prompt) {
             let mut result = String::new();
 
+            // Add notifier part if present (blue)
+            if let Some(notifier) = components.delegate_notifier {
+                result.push_str(&format!("[{}]\n", notifier).blue().to_string());
+            }
+
             // Add profile part if present (cyan)
             if let Some(profile) = components.profile {
                 result.push_str(&format!("[{}] ", profile).cyan().to_string());
@@ -497,6 +505,18 @@ pub fn rl(
         }
     }
 
+    // Add custom keybinding for Ctrl+D to open delegate command (configurable)
+    if ExperimentManager::is_enabled(os, ExperimentName::Delegate) {
+        if let Some(key) = os.database.settings.get_string(Setting::DelegateModeKey) {
+            if key.len() == 1 {
+                rl.bind_sequence(
+                    KeyEvent(KeyCode::Char(key.chars().next().unwrap()), Modifiers::CTRL),
+                    EventHandler::Simple(Cmd::Insert(1, "/delegate ".to_string())),
+                );
+            }
+        };
+    }
+
     // Add custom keybinding for Alt+Enter to insert a newline
     rl.bind_sequence(
         KeyEvent(KeyCode::Enter, Modifiers::ALT),

crates/chat-cli/src/cli/chat/prompt_parser.rs

@@ -3,6 +3,7 @@ use crate::cli::agent::DEFAULT_AGENT_NAME;
 /// Components extracted from a prompt string
 #[derive(Debug, PartialEq)]
 pub struct PromptComponents {
+    pub delegate_notifier: Option<String>,
     pub profile: Option<String>,
     pub warning: bool,
     pub tangent_mode: bool,
@@ -12,12 +13,27 @@ pub struct PromptComponents {
 /// Parse prompt components from a plain text prompt
 pub fn parse_prompt_components(prompt: &str) -> Option<PromptComponents> {
     // Expected format: "[agent] 6% !> " or "> " or "!> " or "[agent] ↯ > " or "6% ↯ > " etc.
+    let mut delegate_notifier = None::<String>;
     let mut profile = None;
     let mut warning = false;
     let mut tangent_mode = false;
     let mut usage_percentage = None;
     let mut remaining = prompt.trim();
 
+    // Check for delegate notifier first
+    if let Some(start) = remaining.find('[') {
+        if let Some(end) = remaining.find(']') {
+            if start < end {
+                let content = &remaining[start + 1..end];
+                // Only set profile if it's not "BACKGROUND TASK READY" or if it doesn't end with newline
+                if content == "BACKGROUND TASK READY" && remaining[end + 1..].starts_with('\n') {
+                    delegate_notifier = Some(content.to_string());
+                    remaining = remaining[end + 1..].trim_start();
+                }
+            }
+        }
+    }
+
     // Check for agent pattern [agent] first
     if let Some(start) = remaining.find('[') {
         if let Some(end) = remaining.find(']') {
@@ -55,6 +71,7 @@ pub fn parse_prompt_components(prompt: &str) -> Option<PromptComponents> {
     // Should end with "> " for both normal and tangent mode
     if remaining.trim_end() == ">" {
         Some(PromptComponents {
+            delegate_notifier,
             profile,
             warning,
             tangent_mode,

crates/chat-cli/src/cli/chat/tool_manager.rs

@@ -71,6 +71,7 @@ use crate::cli::chat::server_messenger::{
     UpdateEventMessage,
 };
 use crate::cli::chat::tools::custom_tool::CustomTool;
+use crate::cli::chat::tools::delegate::Delegate;
 use crate::cli::chat::tools::execute::ExecuteCommand;
 use crate::cli::chat::tools::fs_read::FsRead;
 use crate::cli::chat::tools::fs_write::FsWrite;
@@ -727,6 +728,9 @@ impl ToolManager {
             if !crate::cli::chat::tools::todo::TodoList::is_enabled(os) {
                 tool_specs.remove("todo_list");
             }
+            if !crate::cli::chat::tools::delegate::Delegate::is_enabled(os) {
+                tool_specs.remove("delegate");
+            }
 
             #[cfg(windows)]
             {
@@ -873,6 +877,7 @@ impl ToolManager {
             "knowledge" => Tool::Knowledge(serde_json::from_value::<Knowledge>(value.args).map_err(map_err)?),
             "todo_list" => Tool::Todo(serde_json::from_value::<TodoList>(value.args).map_err(map_err)?),
             // Note that this name is NO LONGER namespaced with server_name{DELIMITER}tool_name
+            "delegate" => Tool::Delegate(serde_json::from_value::<Delegate>(value.args).map_err(map_err)?),
             name => {
                 // Note: tn_map also has tools that underwent no transformation. In otherwords, if
                 // it is a valid tool name, we should get a hit.