task_mcp/mcp/

server.rs

use std::collections::HashMap;
use std::path::PathBuf;
use std::sync::Arc;
use std::time::Duration;

use rmcp::{
    ErrorData as McpError, ServerHandler, ServiceExt,
    handler::server::{tool::ToolRouter, wrapper::Parameters},
    model::{
        CallToolRequestParams, CallToolResult, Content, Implementation, ListToolsResult,
        PaginatedRequestParams, ProtocolVersion, ServerCapabilities, ServerInfo,
    },
    service::{RequestContext, RoleServer},
    tool, tool_router,
    transport::stdio,
};
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use tokio::sync::RwLock;

use crate::config::Config;
use crate::just;
use crate::template;

// =============================================================================
// Public entry point
// =============================================================================

pub async fn run() -> anyhow::Result<()> {
    let config = Config::load();
    let server_cwd = std::env::current_dir()?;
    let server = TaskMcpServer::new(config, server_cwd);
    let service = server.serve(stdio()).await?;
    service.waiting().await?;
    Ok(())
}

// =============================================================================
// MCP Server
// =============================================================================

#[derive(Clone)]
pub struct TaskMcpServer {
    tool_router: ToolRouter<Self>,
    config: Config,
    log_store: Arc<just::TaskLogStore>,
    /// Runtime working directory set by `session_start`.
    workdir: Arc<RwLock<Option<PathBuf>>>,
    /// CWD at server startup (used as default when session_start omits workdir).
    server_cwd: PathBuf,
}

/// Outcome of a lazy auto-session-start attempt.
///
/// Distinguishes the reasons the server may decline to auto-start so that
/// callers can produce actionable error messages and — crucially — recover
/// when a concurrent task has already initialized the session.
#[derive(Debug)]
pub(crate) enum AutoStartOutcome {
    /// Session was newly initialized by this call.
    Started(SessionStartResponse, PathBuf),
    /// Session had already been initialized (by a concurrent task) when we
    /// acquired the write lock. The existing workdir is returned so the
    /// caller can proceed without a spurious error.
    AlreadyStarted(PathBuf),
    /// `server_cwd` is not a ProjectRoot (no `.git`/`justfile` marker).
    NotProjectRoot,
    /// `server_cwd` could not be canonicalized.
    CanonicalizeFailed(std::io::Error),
    /// `server_cwd` is not in `allowed_dirs`.
    NotAllowed(PathBuf),
}

impl TaskMcpServer {
    pub fn new(config: Config, server_cwd: PathBuf) -> Self {
        Self {
            tool_router: Self::tool_router(),
            config,
            log_store: Arc::new(just::TaskLogStore::new(10)),
            workdir: Arc::new(RwLock::new(None)),
            server_cwd,
        }
    }

    /// Try to auto-start a session using `server_cwd` as the workdir.
    ///
    /// See [`AutoStartOutcome`] for the return variants.
    pub(crate) async fn try_auto_session_start(&self) -> AutoStartOutcome {
        // Check if server_cwd is a ProjectRoot (.git or justfile must exist)
        let has_git = tokio::fs::try_exists(self.server_cwd.join(".git"))
            .await
            .unwrap_or(false);
        let has_justfile = tokio::fs::try_exists(self.server_cwd.join("justfile"))
            .await
            .unwrap_or(false);
        if !has_git && !has_justfile {
            return AutoStartOutcome::NotProjectRoot;
        }

        // Canonicalize server_cwd
        let canonical = match tokio::fs::canonicalize(&self.server_cwd).await {
            Ok(p) => p,
            Err(e) => return AutoStartOutcome::CanonicalizeFailed(e),
        };

        // Check allowed_dirs
        if !self.config.is_workdir_allowed(&canonical) {
            return AutoStartOutcome::NotAllowed(canonical);
        }

        // Double-checked locking: acquire write lock, then re-check None.
        // If another task initialized the session between our fast-path read
        // and this write lock, return AlreadyStarted so the caller can reuse
        // the existing workdir instead of reporting a spurious error.
        let mut guard = self.workdir.write().await;
        if let Some(ref existing) = *guard {
            return AutoStartOutcome::AlreadyStarted(existing.clone());
        }
        *guard = Some(canonical.clone());
        drop(guard);

        let justfile =
            resolve_justfile_with_workdir(self.config.justfile_path.as_deref(), &canonical);

        AutoStartOutcome::Started(
            SessionStartResponse {
                workdir: canonical.to_string_lossy().into_owned(),
                justfile: justfile.to_string_lossy().into_owned(),
                mode: mode_label(&self.config),
            },
            canonical,
        )
    }

    /// Return the current session workdir (with optional auto-start) and the auto-start response.
    ///
    /// - If session is already started, returns `(workdir, None)`.
    /// - If not started and `server_cwd` is a ProjectRoot, auto-starts and returns `(workdir, Some(response))`.
    /// - If a concurrent task initialized the session while we were in the slow path, returns `(workdir, None)`.
    /// - Otherwise returns a specific error describing which precondition failed.
    pub(crate) async fn workdir_or_auto(
        &self,
    ) -> Result<(PathBuf, Option<SessionStartResponse>), McpError> {
        // Fast path: session already started
        {
            let guard = self.workdir.read().await;
            if let Some(ref wd) = *guard {
                return Ok((wd.clone(), None));
            }
        }

        // Slow path: try auto-start
        match self.try_auto_session_start().await {
            AutoStartOutcome::Started(resp, wd) => Ok((wd, Some(resp))),
            AutoStartOutcome::AlreadyStarted(wd) => Ok((wd, None)),
            AutoStartOutcome::NotProjectRoot => Err(McpError::internal_error(
                format!(
                    "session not started. server startup CWD {:?} is not a ProjectRoot (no .git or justfile). Call session_start with an explicit workdir.",
                    self.server_cwd
                ),
                None,
            )),
            AutoStartOutcome::CanonicalizeFailed(e) => Err(McpError::internal_error(
                format!(
                    "session not started. failed to canonicalize server startup CWD {:?}: {e}. Call session_start with an explicit workdir.",
                    self.server_cwd
                ),
                None,
            )),
            AutoStartOutcome::NotAllowed(path) => Err(McpError::internal_error(
                format!(
                    "session not started. server startup CWD {:?} is not in allowed_dirs. Call session_start with an allowed workdir.",
                    path
                ),
                None,
            )),
        }
    }
}

// =============================================================================
// ServerHandler impl
// =============================================================================

impl ServerHandler for TaskMcpServer {
    fn get_info(&self) -> ServerInfo {
        ServerInfo {
            protocol_version: ProtocolVersion::V_2025_03_26,
            capabilities: ServerCapabilities::builder().enable_tools().build(),
            server_info: Implementation {
                name: "task-mcp".to_string(),
                title: Some("Task MCP — Agent-safe Task Runner".to_string()),
                description: Some(
                    "Execute predefined justfile tasks safely. \
                     6 tools: session_start, info, init, list, run, logs."
                        .to_string(),
                ),
                version: env!("CARGO_PKG_VERSION").to_string(),
                icons: None,
                website_url: None,
            },
            instructions: Some(
                "Agent-safe task runner backed by just.\n\
                 \n\
                 - `session_start`: Set working directory explicitly. Optional when the \
                 server was launched inside a ProjectRoot (a directory containing `.git` \
                 or `justfile`) — in that case the first `init`/`list`/`run` call auto-starts \
                 the session using the server's startup CWD. Call `session_start` explicitly \
                 only when you need a different workdir (e.g. a subdirectory in a monorepo).\n\
                 - `info`: Show current session state (workdir, mode, etc).\n\
                 - `init`: Generate a justfile in the working directory.\n\
                 - `list`: Show available tasks filtered by [allow-agent] tag.\n\
                 - `run`: Execute a named task.\n\
                 - `logs`: Retrieve execution logs of recent runs.\n\
                 \n\
                 When a call auto-starts the session, the response includes an \
                 `auto_session_start` field with the chosen workdir, justfile, and mode. \
                 Subsequent calls in the same session do not include this field.\n\
                 \n\
                 Only tasks explicitly marked agent-safe are exposed in default mode."
                    .to_string(),
            ),
        }
    }

    async fn list_tools(
        &self,
        _request: Option<PaginatedRequestParams>,
        _context: RequestContext<RoleServer>,
    ) -> Result<ListToolsResult, McpError> {
        Ok(ListToolsResult {
            tools: self.tool_router.list_all(),
            next_cursor: None,
            meta: None,
        })
    }

    async fn call_tool(
        &self,
        request: CallToolRequestParams,
        context: RequestContext<RoleServer>,
    ) -> Result<CallToolResult, McpError> {
        let tool_ctx = rmcp::handler::server::tool::ToolCallContext::new(self, request, context);
        self.tool_router.call(tool_ctx).await
    }
}

// =============================================================================
// Request / Response types
// =============================================================================

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
struct SessionStartRequest {
    /// Working directory path. If omitted or empty, defaults to the server's startup CWD.
    pub workdir: Option<String>,
}

/// Response payload describing a session's working directory, resolved justfile,
/// and active task mode. Returned by `session_start`, and also embedded as
/// `auto_session_start` in other tools' responses when the session was
/// automatically started by that call.
#[derive(Debug, Clone, Serialize)]
pub(crate) struct SessionStartResponse {
    /// Canonicalized absolute path of the working directory.
    pub workdir: String,
    /// Resolved path to the justfile used in this session.
    pub justfile: String,
    /// Active task mode: "agent-only" or "all".
    pub mode: String,
}

#[derive(Debug, Clone, Serialize)]
struct InfoResponse {
    /// Whether session_start has been called.
    pub session_started: bool,
    /// Current working directory (None if session_start not yet called).
    pub workdir: Option<String>,
    /// Resolved justfile path (None if session_start not yet called).
    pub justfile: Option<String>,
    /// Active task mode: "agent-only" or "all".
    pub mode: String,
    /// CWD at server startup.
    pub server_cwd: String,
    /// Whether global justfile merging is enabled.
    pub load_global: bool,
    /// Resolved global justfile path (None when load_global=false or global file not found).
    pub global_justfile: Option<String>,
}

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
struct InitRequest {
    /// Project type: "rust" (default) or "vite-react".
    pub project_type: Option<String>,
    /// Path to a custom template file (must be under session workdir). Overrides TASK_MCP_INIT_TEMPLATE_FILE env.
    pub template_file: Option<String>,
}

#[derive(Debug, Clone, Serialize)]
struct InitResponse {
    /// Path to the generated justfile.
    pub justfile: String,
    /// Project type used for template selection.
    pub project_type: String,
    /// Whether a custom template file was used.
    pub custom_template: bool,
    /// Present only when this call triggered an automatic session_start because
    /// no session was active and the server's startup CWD is a ProjectRoot
    /// (contains `.git` or `justfile`). Contains the resolved workdir, justfile
    /// path, and mode. Absent on subsequent calls within the same session.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub auto_session_start: Option<SessionStartResponse>,
}

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
struct ListRequest {
    /// Filter recipes by group name. If omitted, all agent-safe recipes are returned.
    pub filter: Option<String>,
    /// Justfile path override. Defaults to `justfile` in the current directory.
    pub justfile: Option<String>,
}

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
struct RunRequest {
    /// Name of the recipe to execute (must appear in `list` output).
    pub task_name: String,
    /// Named arguments to pass to the recipe.  Keys must match recipe parameter names.
    pub args: Option<HashMap<String, String>>,
    /// Execution timeout in seconds (default: 60).
    pub timeout_secs: Option<u64>,
}

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
struct LogsRequest {
    /// Retrieve the full output of a specific execution by its UUID.
    /// If omitted, a summary of the 10 most recent executions is returned.
    pub task_id: Option<String>,
    /// When a `task_id` is provided, restrict the stdout to the last N lines.
    /// Ignored when `task_id` is absent.
    pub tail: Option<usize>,
}

// =============================================================================
// Helpers
// =============================================================================

/// Resolve the justfile path taking a session workdir into account.
///
/// If `override_path` is provided it is used as-is (absolute or relative to CWD).
/// Otherwise `{workdir}/justfile` is returned.
fn resolve_justfile_with_workdir(
    override_path: Option<&str>,
    workdir: &std::path::Path,
) -> PathBuf {
    match override_path {
        Some(p) => PathBuf::from(p),
        None => workdir.join("justfile"),
    }
}

/// Return the last `n` lines of `text`.  If `n` exceeds the line count, the
/// full text is returned unchanged.
fn tail_lines(text: &str, n: usize) -> String {
    let lines: Vec<&str> = text.lines().collect();
    if n >= lines.len() {
        return text.to_string();
    }
    lines[lines.len() - n..].join("\n")
}

fn mode_label(config: &Config) -> String {
    use crate::config::TaskMode;
    match config.mode {
        TaskMode::AgentOnly => "agent-only".to_string(),
        TaskMode::All => "all".to_string(),
    }
}

// =============================================================================
// Tool implementations
// =============================================================================

#[tool_router]
impl TaskMcpServer {
    #[tool(
        name = "session_start",
        description = "Set the working directory for this session explicitly. Optional when the server was launched inside a ProjectRoot (directory containing `.git` or `justfile`): the first `init`/`list`/`run` call will auto-start the session using the server's startup CWD. Call this tool to override that default, e.g. when working in a monorepo subdirectory. Subsequent `run` and `list` (without justfile param) use the configured directory.",
        annotations(
            read_only_hint = false,
            destructive_hint = false,
            idempotent_hint = true,
            open_world_hint = false
        )
    )]
    async fn session_start(
        &self,
        Parameters(req): Parameters<SessionStartRequest>,
    ) -> Result<CallToolResult, McpError> {
        // Determine the target directory: use provided path or fall back to server CWD.
        let raw_path = match req.workdir.as_deref() {
            Some(s) if !s.trim().is_empty() => PathBuf::from(s),
            _ => self.server_cwd.clone(),
        };

        // Canonicalize (resolves symlinks, checks existence).
        let canonical = tokio::fs::canonicalize(&raw_path).await.map_err(|e| {
            McpError::invalid_params(
                format!(
                    "workdir {:?} does not exist or is not accessible: {e}",
                    raw_path
                ),
                None,
            )
        })?;

        // Verify against allowed_dirs.
        if !self.config.is_workdir_allowed(&canonical) {
            return Err(McpError::invalid_params(
                format!(
                    "workdir {:?} is not in the allowed directories list",
                    canonical
                ),
                None,
            ));
        }

        // Persist in session state.
        *self.workdir.write().await = Some(canonical.clone());

        let justfile =
            resolve_justfile_with_workdir(self.config.justfile_path.as_deref(), &canonical);

        let response = SessionStartResponse {
            workdir: canonical.to_string_lossy().into_owned(),
            justfile: justfile.to_string_lossy().into_owned(),
            mode: mode_label(&self.config),
        };

        let output = serde_json::to_string_pretty(&response)
            .map_err(|e| McpError::internal_error(e.to_string(), None))?;

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(false),
            meta: None,
        })
    }

    #[tool(
        name = "init",
        description = "Generate a justfile with agent-safe recipes in the session working directory. The session is auto-started if the server was launched inside a ProjectRoot; otherwise call `session_start` first. Supports project types: rust (default), vite-react. Custom template files can also be specified. Fails if justfile already exists — delete it first to regenerate.",
        annotations(
            read_only_hint = false,
            destructive_hint = false,
            idempotent_hint = false,
            open_world_hint = false
        )
    )]
    async fn init(
        &self,
        Parameters(req): Parameters<InitRequest>,
    ) -> Result<CallToolResult, McpError> {
        let (workdir, auto) = self.workdir_or_auto().await?;

        // Parse project type
        let project_type = match req.project_type.as_deref() {
            Some(s) => s
                .parse::<template::ProjectType>()
                .map_err(|e| McpError::invalid_params(e, None))?,
            None => template::ProjectType::default(),
        };

        let justfile_path = workdir.join("justfile");

        // Reject if justfile already exists
        if justfile_path.exists() {
            return Err(McpError::invalid_params(
                format!(
                    "justfile already exists at {}. Delete it first if you want to regenerate.",
                    justfile_path.display()
                ),
                None,
            ));
        }

        // Validate template_file is under workdir (prevent path traversal)
        if let Some(ref tf) = req.template_file {
            let template_path = std::fs::canonicalize(tf).map_err(|e| {
                McpError::invalid_params(
                    format!("template_file {tf:?} is not accessible: {e}"),
                    None,
                )
            })?;
            if !template_path.starts_with(&workdir) {
                return Err(McpError::invalid_params(
                    format!(
                        "template_file must be under session workdir ({}). Got: {}",
                        workdir.display(),
                        template_path.display()
                    ),
                    None,
                ));
            }
        }

        // Resolve template content
        let custom_template_used =
            req.template_file.is_some() || self.config.init_template_file.is_some();

        let content = template::resolve_template(
            project_type,
            req.template_file.as_deref(),
            self.config.init_template_file.as_deref(),
        )
        .await
        .map_err(|e| McpError::internal_error(e.to_string(), None))?;

        // Write justfile
        tokio::fs::write(&justfile_path, &content)
            .await
            .map_err(|e| {
                McpError::internal_error(
                    format!(
                        "failed to write justfile at {}: {e}",
                        justfile_path.display()
                    ),
                    None,
                )
            })?;

        let response = InitResponse {
            justfile: justfile_path.to_string_lossy().into_owned(),
            project_type: project_type.to_string(),
            custom_template: custom_template_used,
            auto_session_start: auto,
        };

        let output = serde_json::to_string_pretty(&response)
            .map_err(|e| McpError::internal_error(e.to_string(), None))?;

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(false),
            meta: None,
        })
    }

    #[tool(
        name = "info",
        description = "Show current session state: workdir, justfile path, mode, and server startup CWD.",
        annotations(
            read_only_hint = true,
            destructive_hint = false,
            idempotent_hint = true,
            open_world_hint = false
        )
    )]
    async fn info(&self) -> Result<CallToolResult, McpError> {
        let current_workdir = self.workdir.read().await.clone();

        let (session_started, workdir_str, justfile_str) = match current_workdir {
            Some(ref wd) => {
                let justfile =
                    resolve_justfile_with_workdir(self.config.justfile_path.as_deref(), wd);
                (
                    true,
                    Some(wd.to_string_lossy().into_owned()),
                    Some(justfile.to_string_lossy().into_owned()),
                )
            }
            None => (false, None, None),
        };

        let global_justfile_str = self
            .config
            .global_justfile_path
            .as_ref()
            .map(|p| p.to_string_lossy().into_owned());

        let response = InfoResponse {
            session_started,
            workdir: workdir_str,
            justfile: justfile_str,
            mode: mode_label(&self.config),
            server_cwd: self.server_cwd.to_string_lossy().into_owned(),
            load_global: self.config.load_global,
            global_justfile: global_justfile_str,
        };

        let output = serde_json::to_string_pretty(&response)
            .map_err(|e| McpError::internal_error(e.to_string(), None))?;

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(false),
            meta: None,
        })
    }

    #[tool(
        name = "list",
        description = "List available tasks from justfile. Returns an object `{\"recipes\": [...]}` containing task names, descriptions, parameters, and groups. When this call triggers an automatic session_start, the response also includes an `auto_session_start` field.",
        annotations(
            read_only_hint = true,
            destructive_hint = false,
            idempotent_hint = true,
            open_world_hint = false
        )
    )]
    async fn list(
        &self,
        Parameters(req): Parameters<ListRequest>,
    ) -> Result<CallToolResult, McpError> {
        let (justfile_path, workdir_opt, auto) = if req.justfile.is_some() {
            // justfile parameter specified → session_start not required
            let jp = just::resolve_justfile_path(
                req.justfile
                    .as_deref()
                    .or(self.config.justfile_path.as_deref()),
                None,
            );
            (jp, None, None)
        } else {
            // no justfile parameter → session_start is required (or auto-started)
            let (wd, auto) = self.workdir_or_auto().await?;
            let jp = just::resolve_justfile_path(self.config.justfile_path.as_deref(), Some(&wd));
            (jp, Some(wd), auto)
        };

        let recipes = if self.config.load_global {
            just::list_recipes_merged(
                &justfile_path,
                self.config.global_justfile_path.as_deref(),
                &self.config.mode,
                workdir_opt.as_deref(),
            )
            .await
            .map_err(|e| McpError::internal_error(e.to_string(), None))?
        } else {
            just::list_recipes(&justfile_path, &self.config.mode, workdir_opt.as_deref())
                .await
                .map_err(|e| McpError::internal_error(e.to_string(), None))?
        };

        // Apply optional group filter
        let filtered: Vec<_> = match &req.filter {
            Some(group) => recipes
                .into_iter()
                .filter(|r| r.groups.iter().any(|g| g == group))
                .collect(),
            None => recipes,
        };

        let mut wrapped = serde_json::json!({ "recipes": filtered });
        if let Some(auto_response) = auto {
            wrapped.as_object_mut().expect("json object").insert(
                "auto_session_start".to_string(),
                serde_json::to_value(auto_response)
                    .map_err(|e| McpError::internal_error(e.to_string(), None))?,
            );
        }
        let output = serde_json::to_string_pretty(&wrapped)
            .map_err(|e| McpError::internal_error(e.to_string(), None))?;

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(false),
            meta: None,
        })
    }

    #[tool(
        name = "run",
        description = "Execute a predefined task. Only tasks visible in `list` can be run.",
        annotations(
            read_only_hint = false,
            destructive_hint = true,
            idempotent_hint = false,
            open_world_hint = false
        )
    )]
    async fn run(
        &self,
        Parameters(req): Parameters<RunRequest>,
    ) -> Result<CallToolResult, McpError> {
        // session_start is required for run (auto-start if ProjectRoot)
        let (workdir, auto) = self.workdir_or_auto().await?;
        let justfile_path =
            just::resolve_justfile_path(self.config.justfile_path.as_deref(), Some(&workdir));
        let args = req.args.unwrap_or_default();
        let timeout = Duration::from_secs(req.timeout_secs.unwrap_or(60));

        let execution = if self.config.load_global {
            just::execute_recipe_merged(
                &req.task_name,
                &args,
                &justfile_path,
                self.config.global_justfile_path.as_deref(),
                timeout,
                &self.config.mode,
                Some(&workdir),
            )
            .await
            .map_err(|e| McpError::internal_error(e.to_string(), None))?
        } else {
            just::execute_recipe(
                &req.task_name,
                &args,
                &justfile_path,
                timeout,
                &self.config.mode,
                Some(&workdir),
            )
            .await
            .map_err(|e| McpError::internal_error(e.to_string(), None))?
        };

        // Persist to log store
        self.log_store.push(execution.clone());

        let is_error = execution.exit_code.map(|c| c != 0).unwrap_or(true);

        let output = match auto {
            Some(auto_response) => {
                let mut val = serde_json::to_value(&execution)
                    .map_err(|e| McpError::internal_error(e.to_string(), None))?;
                if let Some(obj) = val.as_object_mut() {
                    obj.insert(
                        "auto_session_start".to_string(),
                        serde_json::to_value(auto_response)
                            .map_err(|e| McpError::internal_error(e.to_string(), None))?,
                    );
                }
                serde_json::to_string_pretty(&val)
                    .map_err(|e| McpError::internal_error(e.to_string(), None))?
            }
            None => serde_json::to_string_pretty(&execution)
                .map_err(|e| McpError::internal_error(e.to_string(), None))?,
        };

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(is_error),
            meta: None,
        })
    }

    #[tool(
        name = "logs",
        description = "Retrieve execution logs. Returns recent task execution results.",
        annotations(
            read_only_hint = true,
            destructive_hint = false,
            idempotent_hint = true,
            open_world_hint = false
        )
    )]
    async fn logs(
        &self,
        Parameters(req): Parameters<LogsRequest>,
    ) -> Result<CallToolResult, McpError> {
        let output = match req.task_id.as_deref() {
            Some(id) => {
                match self.log_store.get(id) {
                    None => {
                        return Err(McpError::internal_error(
                            format!("execution not found: {id}"),
                            None,
                        ));
                    }
                    Some(mut execution) => {
                        // Apply tail filter if requested
                        if let Some(n) = req.tail {
                            execution.stdout = tail_lines(&execution.stdout, n);
                        }
                        serde_json::to_string_pretty(&execution)
                            .map_err(|e| McpError::internal_error(e.to_string(), None))?
                    }
                }
            }
            None => {
                let summaries = self.log_store.recent(10);
                serde_json::to_string_pretty(&summaries)
                    .map_err(|e| McpError::internal_error(e.to_string(), None))?
            }
        };

        Ok(CallToolResult {
            content: vec![Content::text(output)],
            structured_content: None,
            is_error: Some(false),
            meta: None,
        })
    }
}

// =============================================================================
// Tests
// =============================================================================

#[cfg(test)]
impl TaskMcpServer {
    /// Set the workdir directly (test-only helper).
    pub(crate) async fn set_workdir_for_test(&self, path: PathBuf) {
        *self.workdir.write().await = Some(path);
    }

    /// Read the current workdir (test-only helper).
    pub(crate) async fn current_workdir(&self) -> Option<PathBuf> {
        self.workdir.read().await.clone()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn make_server(server_cwd: PathBuf) -> TaskMcpServer {
        TaskMcpServer::new(Config::default(), server_cwd)
    }

    fn make_server_with_allowed_dirs(
        server_cwd: PathBuf,
        allowed_dirs: Vec<PathBuf>,
    ) -> TaskMcpServer {
        let config = Config {
            allowed_dirs,
            ..Config::default()
        };
        TaskMcpServer::new(config, server_cwd)
    }

    // -------------------------------------------------------------------------
    // try_auto_session_start
    // -------------------------------------------------------------------------

    /// .git ディレクトリがある ProjectRoot で auto-start が成功する。
    #[tokio::test]
    async fn test_try_auto_session_start_in_project_root() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        std::fs::create_dir(tmpdir.path().join(".git")).expect("create .git dir");

        let server = make_server(tmpdir.path().to_path_buf());
        let outcome = server.try_auto_session_start().await;

        match outcome {
            AutoStartOutcome::Started(resp, _wd) => {
                assert_eq!(resp.mode, "agent-only");
            }
            other => panic!("auto-start should succeed in a ProjectRoot (.git), got {other:?}"),
        }
        assert!(
            server.current_workdir().await.is_some(),
            "workdir should be set after auto-start"
        );
    }

    /// 2回目の呼び出しでは auto-start が発生しない (already started)。
    #[tokio::test]
    async fn test_second_call_no_auto_start() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        std::fs::create_dir(tmpdir.path().join(".git")).expect("create .git dir");

        let server = make_server(tmpdir.path().to_path_buf());

        // 1回目: auto-start 発生
        let (_, auto1) = server
            .workdir_or_auto()
            .await
            .expect("first call should succeed");
        assert!(auto1.is_some(), "first call should trigger auto-start");

        // 2回目: workdir は既に設定済み → auto なし
        let (_, auto2) = server
            .workdir_or_auto()
            .await
            .expect("second call should succeed");
        assert!(
            auto2.is_none(),
            "second call must NOT return auto_session_start"
        );
    }

    /// marker なし (非 ProjectRoot) では auto-start しない → error。
    #[tokio::test]
    async fn test_no_auto_start_in_non_project_root() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        // .git も justfile も作成しない

        let server = make_server(tmpdir.path().to_path_buf());
        let result = server.workdir_or_auto().await;

        let err = result.expect_err("should fail when no ProjectRoot marker");
        assert!(
            err.message.contains("not a ProjectRoot"),
            "error message should identify 'not a ProjectRoot': {err:?}"
        );
    }

    /// justfile のみ存在する場合でも auto-start が成功する。
    #[tokio::test]
    async fn test_justfile_marker_also_triggers() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        // .git はなく justfile のみ
        std::fs::write(tmpdir.path().join("justfile"), "").expect("create justfile");

        let server = make_server(tmpdir.path().to_path_buf());
        let outcome = server.try_auto_session_start().await;

        assert!(
            matches!(outcome, AutoStartOutcome::Started(_, _)),
            "auto-start should succeed with only justfile marker, got {outcome:?}"
        );
    }

    /// allowed_dirs 違反の場合は auto-start しない → error (原因が区別される)。
    #[tokio::test]
    async fn test_allowed_dirs_violation_no_auto_start() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        std::fs::create_dir(tmpdir.path().join(".git")).expect("create .git dir");

        let other_dir = tempfile::tempdir().expect("create other tempdir");
        let allowed = vec![other_dir.path().to_path_buf()];

        let server = make_server_with_allowed_dirs(tmpdir.path().to_path_buf(), allowed);
        let err = server
            .workdir_or_auto()
            .await
            .expect_err("should fail when server_cwd is not in allowed_dirs");
        assert!(
            err.message.contains("allowed_dirs"),
            "error message should identify the allowed_dirs violation: {err:?}"
        );
    }

    /// HIGH-1 regression: `try_auto_session_start` が並行初期化済みの状態で
    /// `AlreadyStarted` を返し、`workdir_or_auto` 経由では誤エラーにならない。
    #[tokio::test]
    async fn test_auto_start_already_started_variant() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        std::fs::create_dir(tmpdir.path().join(".git")).expect("create .git dir");

        let server = make_server(tmpdir.path().to_path_buf());

        // 並行初期化を模倣: 直接 workdir を設定してから slow path を叩く。
        let pre_set = tmpdir.path().join("pre-set");
        std::fs::create_dir(&pre_set).expect("create pre-set dir");
        server.set_workdir_for_test(pre_set.clone()).await;

        let outcome = server.try_auto_session_start().await;
        match outcome {
            AutoStartOutcome::AlreadyStarted(wd) => assert_eq!(wd, pre_set),
            other => panic!("expected AlreadyStarted, got {other:?}"),
        }
    }

    /// ProjectRoot でも明示 session_start (workdir=subdir) 後には auto がない。
    #[tokio::test]
    async fn test_explicit_session_start_overrides() {
        let tmpdir = tempfile::tempdir().expect("create tempdir");
        std::fs::create_dir(tmpdir.path().join(".git")).expect("create .git dir");

        // subdir を作って明示的に workdir をセット
        let subdir = tmpdir.path().join("subdir");
        std::fs::create_dir(&subdir).expect("create subdir");

        let server = make_server(tmpdir.path().to_path_buf());
        // 明示的な session_start を模倣して workdir を直接セット
        server.set_workdir_for_test(subdir.clone()).await;

        // workdir_or_auto を呼んでも auto は発生しない (already started)
        let result = server.workdir_or_auto().await;
        assert!(result.is_ok());
        let (wd, auto) = result.unwrap();
        assert!(
            auto.is_none(),
            "after explicit session_start, auto_session_start must be None"
        );
        // workdir は subdir (server_cwd ではない)
        assert_eq!(
            wd, subdir,
            "workdir should be the explicitly set subdir, not server_cwd"
        );
    }
}