subagent tool: add option to run in a different directory

hive-subagent-mcp/src/mcp.rs

@@ -37,6 +37,15 @@ struct StartArgs {
     /// belongs in `prompt_file`, not here.
     #[serde(default = "default_trigger")]
     trigger: String,
+    /// Working directory for the subagent's session — e.g. a git worktree
+    /// you've already prepared for it, so a parallel batch of subagents
+    /// never race on the same working tree. Must exist. Omit to inherit
+    /// this daemon's own working directory (today's default). Claude
+    /// derives its per-project session storage from this path, so
+    /// `continue`/`status` against this name must pass this exact same
+    /// `dir` again to find the session — see those tools' own docs.
+    #[serde(default)]
+    dir: Option<String>,
 }
 
 fn default_trigger() -> String {
@@ -53,12 +62,22 @@ struct ContinueArgs {
     /// default — this does not have to match whatever model `start` used.
     #[serde(default)]
     model: Option<String>,
+    /// The same `dir` given at `start`, if any — sessions are stored keyed
+    /// by directory, so a different (or omitted) `dir` here looks in the
+    /// wrong place and reports no session found under `name` even though
+    /// one exists.
+    #[serde(default)]
+    dir: Option<String>,
 }
 
 #[derive(Debug, Deserialize, JsonSchema)]
 struct StatusArgs {
     /// The subagent name to check.
     name: String,
+    /// The same `dir` given at `start`, if any — see `continue`'s `dir` doc
+    /// for why this has to match.
+    #[serde(default)]
+    dir: Option<String>,
 }
 
 #[derive(Debug, Deserialize, JsonSchema)]
@@ -95,6 +114,7 @@ impl SubagentMcp {
             args.model,
             &args.prompt_file,
             args.trigger,
+            args.dir.as_deref(),
         ) {
             Ok(msg) => msg,
             Err(e) => format!("start error: {e:#}"),
@@ -110,7 +130,13 @@ impl SubagentMcp {
             `start`. Refuses a name with no session on disk at all, or one already running."
     )]
     fn r#continue(&self, Parameters(args): Parameters<ContinueArgs>) -> String {
-        match session::continue_(&self.state, &args.name, args.prompt, args.model) {
+        match session::continue_(
+            &self.state,
+            &args.name,
+            args.prompt,
+            args.model,
+            args.dir.as_deref(),
+        ) {
             Ok(msg) => msg,
             Err(e) => format!("continue error: {e:#}"),
         }
@@ -138,7 +164,7 @@ impl SubagentMcp {
             `continue` to give it another turn), and no such session at all."
     )]
     fn status(&self, Parameters(args): Parameters<StatusArgs>) -> String {
-        match session::status(&self.state, &args.name) {
+        match session::status(&self.state, &args.name, args.dir.as_deref()) {
             Ok(msg) => msg,
             Err(e) => format!("status error: {e:#}"),
         }

hive-subagent-mcp/src/session.rs

@@ -118,9 +118,17 @@ fn subagent_otel_attrs(name: &str) -> String {
 
 /// Build the `Config` one subagent turn runs against. `prompt_file`, when
 /// given, becomes `--append-system-prompt-file` — the subagent's task
-/// instructions. Always `--dangerously-skip-permissions --strict-mcp-config`
-/// (no `--mcp-config` override — a safety property, not a knob).
-fn build_config(name: &str, model: Option<String>, prompt_file: Option<&str>) -> Config {
+/// instructions. `dir`, when given, becomes `Config::cwd` (e.g. a worktree
+/// the caller already prepared); `None` inherits this daemon's own working
+/// directory, same as before this field existed. Always
+/// `--dangerously-skip-permissions --strict-mcp-config` (no `--mcp-config`
+/// override — a safety property, not a knob).
+fn build_config(
+    name: &str,
+    model: Option<String>,
+    prompt_file: Option<&str>,
+    dir: Option<&str>,
+) -> Config {
     let mut extra_args = vec!["--dangerously-skip-permissions".to_owned()];
     if let Some(path) = prompt_file {
         extra_args.push("--append-system-prompt-file".to_owned());
@@ -128,6 +136,7 @@ fn build_config(name: &str, model: Option<String>, prompt_file: Option<&str>) ->
     }
     Config {
         model,
+        cwd: dir.map(PathBuf::from),
         strict_mcp_config: true,
         extra_args,
         env: vec![(
@@ -167,12 +176,13 @@ pub fn start(
     model: Option<String>,
     prompt_file: &str,
     trigger: String,
+    dir: Option<&str>,
 ) -> anyhow::Result<String> {
     validate_name(name)?;
     if !state.reserve(name) {
         anyhow::bail!("subagent `{name}` is already running — use `continue` or `interrupt`");
     }
-    let result = start_reserved(state, name, model, prompt_file, trigger);
+    let result = start_reserved(state, name, model, prompt_file, trigger, dir);
     if result.is_err() {
         state.release_reservation(name);
     }
@@ -189,8 +199,9 @@ fn start_reserved(
     model: Option<String>,
     prompt_file: &str,
     trigger: String,
+    dir: Option<&str>,
 ) -> anyhow::Result<String> {
-    let config = build_config(name, model, Some(prompt_file));
+    let config = build_config(name, model, Some(prompt_file), dir);
     let store = build_store(&config)?;
     if store.find_by_title(name).is_some() {
         tracing::info!(
@@ -225,6 +236,7 @@ pub fn continue_(
     name: &str,
     prompt: String,
     model: Option<String>,
+    dir: Option<&str>,
 ) -> anyhow::Result<String> {
     validate_name(name)?;
     if !state.reserve(name) {
@@ -232,7 +244,7 @@ pub fn continue_(
             "subagent `{name}` is already running — use `interrupt` first if you meant to redirect it"
         );
     }
-    let result = continue_reserved(state, name, prompt, model);
+    let result = continue_reserved(state, name, prompt, model, dir);
     if result.is_err() {
         state.release_reservation(name);
     }
@@ -247,8 +259,9 @@ fn continue_reserved(
     name: &str,
     prompt: String,
     model: Option<String>,
+    dir: Option<&str>,
 ) -> anyhow::Result<String> {
-    let config = build_config(name, model, None);
+    let config = build_config(name, model, None, dir);
     let store = build_store(&config)?;
     if store.find_by_title(name).is_none() {
         anyhow::bail!(
@@ -321,7 +334,7 @@ fn spawn_and_track(
 /// # Errors
 ///
 /// An invalid name, or no session — running or on disk — under `name`.
-pub fn status(state: &State, name: &str) -> anyhow::Result<String> {
+pub fn status(state: &State, name: &str, dir: Option<&str>) -> anyhow::Result<String> {
     validate_name(name)?;
     match state.occupancy(name) {
         Some(true) => return Ok(format!("subagent `{name}` is running")),
@@ -332,7 +345,7 @@ pub fn status(state: &State, name: &str) -> anyhow::Result<String> {
         }
         None => {}
     }
-    let config = build_config(name, None, None);
+    let config = build_config(name, None, None, dir);
     let store = build_store(&config)?;
     if store.find_by_title(name).is_some() {
         Ok(format!(
@@ -472,18 +485,27 @@ mod tests {
 
     #[test]
     fn build_config_only_appends_system_prompt_when_given() {
-        let with = build_config("n", None, Some("/tmp/p.md"));
+        let with = build_config("n", None, Some("/tmp/p.md"), None);
         assert!(
             with.extra_args
                 .contains(&"--append-system-prompt-file".to_owned())
         );
         assert!(with.extra_args.contains(&"/tmp/p.md".to_owned()));
 
-        let without = build_config("n", None, None);
+        let without = build_config("n", None, None, None);
         assert!(
             !without
                 .extra_args
                 .contains(&"--append-system-prompt-file".to_owned())
         );
     }
+
+    #[test]
+    fn build_config_sets_cwd_only_when_a_dir_is_given() {
+        let with = build_config("n", None, None, Some("/tmp/some-worktree"));
+        assert_eq!(with.cwd, Some(PathBuf::from("/tmp/some-worktree")));
+
+        let without = build_config("n", None, None, None);
+        assert_eq!(without.cwd, None);
+    }
 }