Add SpawnSubagentTool

crates/agent/src/thread.rs

@@ -2,8 +2,8 @@ use crate::{
     ContextServerRegistry, CopyPathTool, CreateDirectoryTool, DbLanguageModel, DbThread,
     DeletePathTool, DiagnosticsTool, EditFileTool, FetchTool, FindPathTool, GrepTool,
     ListDirectoryTool, MovePathTool, NowTool, OpenTool, ProjectSnapshot, ReadFileTool,
-    RestoreFileFromDiskTool, SaveFileTool, SystemPromptTemplate, Template, Templates, TerminalTool,
-    ThinkingTool, WebSearchTool,
+    RestoreFileFromDiskTool, SaveFileTool, SpawnSubagentTool, SystemPromptTemplate, Template,
+    Templates, TerminalTool, ThinkingTool, WebSearchTool,
 };
 use acp_thread::{MentionUri, UserMessageId};
 use action_log::ActionLog;
@@ -1011,6 +1011,7 @@ impl Thread {
         ));
         self.add_tool(SaveFileTool::new(self.project.clone()));
         self.add_tool(RestoreFileFromDiskTool::new(self.project.clone()));
+        self.add_tool(SpawnSubagentTool::new(None));
         self.add_tool(TerminalTool::new(self.project.clone(), environment));
         self.add_tool(ThinkingTool);
         self.add_tool(WebSearchTool);

crates/agent/src/tools.rs

@@ -14,6 +14,7 @@ mod open_tool;
 mod read_file_tool;
 mod restore_file_from_disk_tool;
 mod save_file_tool;
+mod spawn_subagent_tool;
 
 mod terminal_tool;
 mod thinking_tool;
@@ -38,6 +39,7 @@ pub use open_tool::*;
 pub use read_file_tool::*;
 pub use restore_file_from_disk_tool::*;
 pub use save_file_tool::*;
+pub use spawn_subagent_tool::*;
 
 pub use terminal_tool::*;
 pub use thinking_tool::*;
@@ -96,6 +98,7 @@ tools! {
     ReadFileTool,
     RestoreFileFromDiskTool,
     SaveFileTool,
+    SpawnSubagentTool,
     TerminalTool,
     ThinkingTool,
     WebSearchTool,

crates/agent/src/tools/spawn_subagent_tool.rs

@@ -0,0 +1,221 @@
+use crate::{AgentTool, ToolCallEventStream};
+use agent_client_protocol as acp;
+use anyhow::{Result, anyhow};
+use gpui::{App, AsyncApp, SharedString, Task};
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use std::sync::Arc;
+
+/// Spawn a subagent (child thread) that can be visited while it runs, and returns a value to the parent.
+///
+/// Note: This file intentionally defines only the tool surface and streaming updates. The actual
+/// spawning/navigation plumbing requires a host capability (session manager + UI) that is not yet
+/// present in the native agent tool environment. Until that capability is wired in, this tool will
+/// fail with a clear error.
+///
+/// Expected design (to be implemented in the host):
+/// - The tool is constructed with a `SubagentHost` implementation that can:
+///   - create a child session/thread
+///   - stream child progress updates
+///   - complete with a final return value
+///   - provide a navigable URI for the UI (e.g. `zed://agent/thread/<session_id>`)
+///
+/// The tool then:
+/// - emits a `ResourceLink` pointing at the child thread so users can open it
+/// - streams progress into the tool call card as markdown
+/// - resolves with the child's final return value (string)
+#[derive(JsonSchema, Serialize, Deserialize)]
+pub struct SpawnSubagentToolInput {
+    /// A short label/title for the subagent.
+    pub title: String,
+
+    /// The instructions to run in the subagent.
+    pub prompt: String,
+
+    /// Optional: profile id to use for the subagent.
+    #[serde(default)]
+    pub profile_id: Option<String>,
+}
+
+/// The final return value from the subagent.
+pub type SpawnSubagentToolOutput = String;
+
+/// Host interface required to implement spawning + streaming + returning.
+///
+/// This is intentionally minimal and object-safe to allow injecting a host backed by `NativeAgent`.
+pub trait SubagentHost: Send + Sync + 'static {
+    /// Start a child subagent session and return a handle containing a navigable URI plus a stream
+    /// of progress updates and a final result.
+    ///
+    /// The returned `SubagentRun` must:
+    /// - yield `Progress` updates in-order
+    /// - eventually yield exactly one `Final` or `Error`
+    fn spawn_subagent(
+        &self,
+        title: String,
+        prompt: String,
+        profile_id: Option<String>,
+        cx: &mut AsyncApp,
+    ) -> Task<Result<SubagentRun>>;
+}
+
+/// A handle for a running subagent.
+pub struct SubagentRun {
+    /// URI that the UI can open to navigate to the child thread.
+    pub thread_uri: String,
+
+    /// A human-friendly label for the link.
+    pub thread_label: String,
+
+    /// Progress stream for tool UI updates.
+    pub updates: futures::channel::mpsc::UnboundedReceiver<SubagentUpdate>,
+}
+
+pub enum SubagentUpdate {
+    /// A streaming progress chunk (e.g. "thinking…", partial summary, etc).
+    Progress(String),
+
+    /// The final return value for the parent.
+    Final(String),
+
+    /// Terminal error.
+    Error(anyhow::Error),
+}
+
+pub struct SpawnSubagentTool {
+    host: Option<Arc<dyn SubagentHost>>,
+}
+
+impl SpawnSubagentTool {
+    pub fn new(host: Option<Arc<dyn SubagentHost>>) -> Self {
+        Self { host }
+    }
+}
+
+impl AgentTool for SpawnSubagentTool {
+    type Input = SpawnSubagentToolInput;
+    type Output = SpawnSubagentToolOutput;
+
+    fn name() -> &'static str {
+        "spawn_subagent"
+    }
+
+    fn kind() -> acp::ToolKind {
+        acp::ToolKind::Other
+    }
+
+    fn description() -> SharedString {
+        "Spawns a child Zed Agent thread (subagent), streams its progress, and returns its final value to the parent."
+            .into()
+    }
+
+    fn initial_title(
+        &self,
+        input: Result<Self::Input, serde_json::Value>,
+        _cx: &mut App,
+    ) -> SharedString {
+        if let Ok(input) = input {
+            format!("Spawn subagent: {}", input.title).into()
+        } else {
+            "Spawn subagent".into()
+        }
+    }
+
+    fn run(
+        self: Arc<Self>,
+        input: Self::Input,
+        event_stream: ToolCallEventStream,
+        cx: &mut App,
+    ) -> Task<Result<Self::Output>> {
+        let Some(host) = self.host.clone() else {
+            return Task::ready(Err(anyhow!(
+                "spawn_subagent is not available: native agent host capability is not wired into tools yet"
+            )));
+        };
+
+        let title = input.title;
+        let prompt = input.prompt;
+        let profile_id = input.profile_id;
+
+        cx.spawn(async move |cx| {
+            // Start the child run via host.
+            let mut run = host
+                .spawn_subagent(title.clone(), prompt, profile_id, cx)
+                .await?;
+
+            // Emit a link to the child thread so the user can open/visit it.
+            event_stream.update_fields(
+                acp::ToolCallUpdateFields::new().content(vec![acp::ToolCallContent::Content(
+                    acp::Content::new(acp::ContentBlock::ResourceLink(
+                        acp::ResourceLink::new(run.thread_label.clone(), run.thread_uri.clone())
+                            .title(run.thread_label.clone()),
+                    )),
+                )]),
+            );
+
+            // Stream progress as markdown appended below the link.
+            let mut accumulated_progress = String::new();
+            while let Some(update) = run.updates.next().await {
+                match update {
+                    SubagentUpdate::Progress(chunk) => {
+                        if !accumulated_progress.is_empty() {
+                            accumulated_progress.push('\n');
+                        }
+                        accumulated_progress.push_str(&chunk);
+
+                        event_stream.update_fields(
+                            acp::ToolCallUpdateFields::new().content(vec![
+                                acp::ToolCallContent::Content(acp::Content::new(
+                                    acp::ContentBlock::ResourceLink(
+                                        acp::ResourceLink::new(
+                                            run.thread_label.clone(),
+                                            run.thread_uri.clone(),
+                                        )
+                                        .title(run.thread_label.clone()),
+                                    ),
+                                )),
+                                acp::ToolCallContent::Content(acp::Content::new(
+                                    acp::ContentBlock::Text(acp::TextContent::new(
+                                        format!("### Subagent progress\n\n{}", accumulated_progress),
+                                    )),
+                                )),
+                            ]),
+                        );
+                    }
+                    SubagentUpdate::Final(value) => {
+                        // Final update for UI (optional).
+                        event_stream.update_fields(
+                            acp::ToolCallUpdateFields::new().content(vec![
+                                acp::ToolCallContent::Content(acp::Content::new(
+                                    acp::ContentBlock::ResourceLink(
+                                        acp::ResourceLink::new(
+                                            run.thread_label.clone(),
+                                            run.thread_uri.clone(),
+                                        )
+                                        .title(run.thread_label.clone()),
+                                    ),
+                                )),
+                                acp::ToolCallContent::Content(acp::Content::new(
+                                    acp::ContentBlock::Text(acp::TextContent::new(format!(
+                                        "### Subagent returned\n\n{}",
+                                        value
+                                    ))),
+                                )),
+                            ]),
+                        );
+
+                        return Ok(value);
+                    }
+                    SubagentUpdate::Error(error) => {
+                        return Err(error);
+                    }
+                }
+            }
+
+            Err(anyhow!("subagent stream ended without producing a final value"))
+        })
+    }
+}
+
+// futures::StreamExt is only needed in the async run implementation; keep it scoped here.
+use futures::StreamExt as _;