feat: add Landlock sandbox for sidecar process isolation

SandboxConfig with RW/RO paths applied via pre_exec() in sidecar child
process. Requires kernel 6.2+ with graceful fallback. Per-project toggle
in SettingsTab. 9 unit tests.

v2/bterminal-core/Cargo.toml

@@ -12,3 +12,4 @@ log = "0.4"
 portable-pty = "0.8"
 uuid = { version = "1", features = ["v4"] }
 dirs = "5"
+landlock = "0.4"

v2/bterminal-core/src/config.rs

@@ -95,6 +95,11 @@ impl AppConfig {
         self.config_dir.join("groups.json")
     }
 
+    /// Path to plugins directory
+    pub fn plugins_dir(&self) -> PathBuf {
+        self.config_dir.join("plugins")
+    }
+
     /// Whether running in test mode (BTERMINAL_TEST=1)
     pub fn is_test_mode(&self) -> bool {
         self.test_mode

v2/bterminal-core/src/sandbox.rs

@@ -0,0 +1,270 @@
+// Landlock-based filesystem sandboxing for sidecar processes.
+//
+// Landlock is a Linux Security Module (LSM) available since kernel 5.13.
+// It restricts filesystem access for the calling process and all its children.
+// Applied via pre_exec() on the sidecar child process before exec.
+//
+// Restrictions can only be tightened after application — never relaxed.
+// The sidecar is long-lived and handles queries for multiple projects,
+// so we apply the union of all project paths at sidecar start time.
+
+use std::path::PathBuf;
+
+use landlock::{
+    Access, AccessFs, PathBeneath, PathFd, Ruleset, RulesetAttr, RulesetCreatedAttr,
+    RulesetStatus, ABI,
+};
+
+/// Target Landlock ABI version. V3 requires kernel 6.2+ (we run 6.12+).
+/// Falls back gracefully on older kernels via best-effort mode.
+const TARGET_ABI: ABI = ABI::V3;
+
+/// Configuration for Landlock filesystem sandboxing.
+#[derive(Debug, Clone)]
+pub struct SandboxConfig {
+    /// Directories with full read+write+execute access (project CWDs, worktrees, tmp)
+    pub rw_paths: Vec<PathBuf>,
+    /// Directories with read-only access (system libs, runtimes, config)
+    pub ro_paths: Vec<PathBuf>,
+    /// Whether sandboxing is enabled
+    pub enabled: bool,
+}
+
+impl Default for SandboxConfig {
+    fn default() -> Self {
+        Self {
+            rw_paths: Vec::new(),
+            ro_paths: Vec::new(),
+            enabled: false,
+        }
+    }
+}
+
+impl SandboxConfig {
+    /// Build a sandbox config for a set of project directories.
+    ///
+    /// `project_cwds` — directories that need read+write access (one per project).
+    /// `worktree_roots` — optional worktree directories (one per project that uses worktrees).
+    ///
+    /// System paths (runtimes, libraries, /etc) are added as read-only automatically.
+    pub fn for_projects(project_cwds: &[&str], worktree_roots: &[&str]) -> Self {
+        let mut rw = Vec::new();
+
+        for cwd in project_cwds {
+            rw.push(PathBuf::from(cwd));
+        }
+        for wt in worktree_roots {
+            rw.push(PathBuf::from(wt));
+        }
+
+        // Temp dir for sidecar scratch files
+        rw.push(std::env::temp_dir());
+
+        let home = dirs::home_dir().unwrap_or_else(|| PathBuf::from("/root"));
+
+        let ro = vec![
+            PathBuf::from("/usr"),     // system binaries + libraries
+            PathBuf::from("/lib"),     // shared libraries
+            PathBuf::from("/lib64"),   // 64-bit shared libraries
+            PathBuf::from("/etc"),     // system configuration (read only)
+            PathBuf::from("/proc"),    // process info (Landlock V3+ handles this)
+            PathBuf::from("/dev"),     // device nodes (stdin/stdout/stderr, /dev/null, urandom)
+            PathBuf::from("/bin"),     // essential binaries (symlink to /usr/bin on most distros)
+            PathBuf::from("/sbin"),    // essential system binaries
+            home.join(".local"),       // ~/.local/bin (claude CLI, user-installed tools)
+            home.join(".deno"),        // Deno runtime cache
+            home.join(".nvm"),         // Node.js version manager
+            home.join(".config"),      // XDG config (claude profiles, bterminal config)
+            home.join(".claude"),      // Claude CLI data (worktrees, skills, settings)
+        ];
+
+        Self {
+            rw_paths: rw,
+            ro_paths: ro,
+            enabled: true,
+        }
+    }
+
+    /// Build a sandbox config for a single project directory.
+    pub fn for_project(cwd: &str, worktree: Option<&str>) -> Self {
+        let worktrees: Vec<&str> = worktree.into_iter().collect();
+        Self::for_projects(&[cwd], &worktrees)
+    }
+
+    /// Apply Landlock restrictions to the current process.
+    ///
+    /// This must be called in the child process (e.g., via `pre_exec`) BEFORE exec.
+    /// Once applied, restrictions are inherited by all child processes and cannot be relaxed.
+    ///
+    /// Returns:
+    /// - `Ok(true)` if Landlock was applied and enforced
+    /// - `Ok(false)` if the kernel does not support Landlock (graceful degradation)
+    /// - `Err(msg)` on configuration or syscall errors
+    pub fn apply(&self) -> Result<bool, String> {
+        if !self.enabled {
+            return Ok(false);
+        }
+
+        let access_all = AccessFs::from_all(TARGET_ABI);
+        let access_read = AccessFs::from_read(TARGET_ABI);
+
+        // Create ruleset handling all filesystem access types
+        let mut ruleset = Ruleset::default()
+            .handle_access(access_all)
+            .map_err(|e| format!("Landlock: failed to handle access: {e}"))?
+            .create()
+            .map_err(|e| format!("Landlock: failed to create ruleset: {e}"))?;
+
+        // Add read+write rules for project directories and tmp
+        for path in &self.rw_paths {
+            if path.exists() {
+                let fd = PathFd::new(path)
+                    .map_err(|e| format!("Landlock: PathFd failed for {}: {e}", path.display()))?;
+                ruleset = ruleset
+                    .add_rule(PathBeneath::new(fd, access_all))
+                    .map_err(|e| {
+                        format!("Landlock: add_rule (rw) failed for {}: {e}", path.display())
+                    })?;
+            } else {
+                log::warn!(
+                    "Landlock: skipping non-existent rw path: {}",
+                    path.display()
+                );
+            }
+        }
+
+        // Add read-only rules for system paths
+        for path in &self.ro_paths {
+            if path.exists() {
+                let fd = PathFd::new(path)
+                    .map_err(|e| format!("Landlock: PathFd failed for {}: {e}", path.display()))?;
+                ruleset = ruleset
+                    .add_rule(PathBeneath::new(fd, access_read))
+                    .map_err(|e| {
+                        format!("Landlock: add_rule (ro) failed for {}: {e}", path.display())
+                    })?;
+            }
+            // Silently skip non-existent read-only paths (e.g., /lib64 on some systems)
+        }
+
+        // Enforce the ruleset on this thread (and inherited by children)
+        let status = ruleset
+            .restrict_self()
+            .map_err(|e| format!("Landlock: restrict_self failed: {e}"))?;
+
+        let enforced = status.ruleset != RulesetStatus::NotEnforced;
+        if enforced {
+            log::info!("Landlock sandbox applied ({} rw, {} ro paths)", self.rw_paths.len(), self.ro_paths.len());
+        } else {
+            log::warn!("Landlock sandbox was not enforced (kernel may lack support)");
+        }
+
+        Ok(enforced)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_default_is_disabled() {
+        let config = SandboxConfig::default();
+        assert!(!config.enabled);
+        assert!(config.rw_paths.is_empty());
+        assert!(config.ro_paths.is_empty());
+    }
+
+    #[test]
+    fn test_for_project_single_cwd() {
+        let config = SandboxConfig::for_project("/home/user/myproject", None);
+        assert!(config.enabled);
+        assert!(config.rw_paths.contains(&PathBuf::from("/home/user/myproject")));
+        assert!(config.rw_paths.contains(&std::env::temp_dir()));
+        // No worktree path added
+        assert!(!config
+            .rw_paths
+            .iter()
+            .any(|p| p.to_string_lossy().contains("worktree")));
+    }
+
+    #[test]
+    fn test_for_project_with_worktree() {
+        let config = SandboxConfig::for_project(
+            "/home/user/myproject",
+            Some("/home/user/myproject/.claude/worktrees/abc123"),
+        );
+        assert!(config.enabled);
+        assert!(config.rw_paths.contains(&PathBuf::from("/home/user/myproject")));
+        assert!(config.rw_paths.contains(&PathBuf::from(
+            "/home/user/myproject/.claude/worktrees/abc123"
+        )));
+    }
+
+    #[test]
+    fn test_for_projects_multiple_cwds() {
+        let config = SandboxConfig::for_projects(
+            &["/home/user/project-a", "/home/user/project-b"],
+            &["/home/user/project-a/.claude/worktrees/s1"],
+        );
+        assert!(config.enabled);
+        assert!(config.rw_paths.contains(&PathBuf::from("/home/user/project-a")));
+        assert!(config.rw_paths.contains(&PathBuf::from("/home/user/project-b")));
+        assert!(config.rw_paths.contains(&PathBuf::from(
+            "/home/user/project-a/.claude/worktrees/s1"
+        )));
+        // tmp always present
+        assert!(config.rw_paths.contains(&std::env::temp_dir()));
+    }
+
+    #[test]
+    fn test_ro_paths_include_system_dirs() {
+        let config = SandboxConfig::for_project("/tmp/test", None);
+        let ro_strs: Vec<String> = config.ro_paths.iter().map(|p| p.display().to_string()).collect();
+
+        assert!(ro_strs.iter().any(|p| p == "/usr"), "missing /usr");
+        assert!(ro_strs.iter().any(|p| p == "/lib"), "missing /lib");
+        assert!(ro_strs.iter().any(|p| p == "/etc"), "missing /etc");
+        assert!(ro_strs.iter().any(|p| p == "/proc"), "missing /proc");
+        assert!(ro_strs.iter().any(|p| p == "/dev"), "missing /dev");
+        assert!(ro_strs.iter().any(|p| p == "/bin"), "missing /bin");
+    }
+
+    #[test]
+    fn test_ro_paths_include_runtime_dirs() {
+        let config = SandboxConfig::for_project("/tmp/test", None);
+        let home = dirs::home_dir().unwrap();
+
+        assert!(config.ro_paths.contains(&home.join(".local")));
+        assert!(config.ro_paths.contains(&home.join(".deno")));
+        assert!(config.ro_paths.contains(&home.join(".nvm")));
+        assert!(config.ro_paths.contains(&home.join(".config")));
+        assert!(config.ro_paths.contains(&home.join(".claude")));
+    }
+
+    #[test]
+    fn test_disabled_apply_returns_false() {
+        let config = SandboxConfig::default();
+        assert_eq!(config.apply().unwrap(), false);
+    }
+
+    #[test]
+    fn test_rw_paths_count() {
+        // Single project: cwd + tmp = 2
+        let config = SandboxConfig::for_project("/tmp/test", None);
+        assert_eq!(config.rw_paths.len(), 2);
+
+        // With worktree: cwd + worktree + tmp = 3
+        let config = SandboxConfig::for_project("/tmp/test", Some("/tmp/wt"));
+        assert_eq!(config.rw_paths.len(), 3);
+    }
+
+    #[test]
+    fn test_for_projects_empty() {
+        let config = SandboxConfig::for_projects(&[], &[]);
+        assert!(config.enabled);
+        // Only tmp dir in rw
+        assert_eq!(config.rw_paths.len(), 1);
+        assert_eq!(config.rw_paths[0], std::env::temp_dir());
+    }
+}

v2/bterminal-core/src/sidecar.rs

@@ -3,12 +3,15 @@
 
 use serde::{Deserialize, Serialize};
 use std::io::{BufRead, BufReader, Write};
+#[cfg(unix)]
+use std::os::unix::process::CommandExt;
 use std::path::PathBuf;
 use std::process::{Child, Command, Stdio};
 use std::sync::{Arc, Mutex};
 use std::thread;
 
 use crate::event::EventSink;
+use crate::sandbox::SandboxConfig;
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct AgentQueryOptions {
@@ -46,6 +49,8 @@ pub struct SidecarConfig {
     pub search_paths: Vec<PathBuf>,
     /// Extra env vars forwarded to sidecar processes (e.g. BTERMINAL_TEST=1 for test isolation)
     pub env_overrides: std::collections::HashMap<String, String>,
+    /// Landlock filesystem sandbox configuration (Linux 5.13+, applied via pre_exec)
+    pub sandbox: SandboxConfig,
 }
 
 struct SidecarCommand {
@@ -58,7 +63,7 @@ pub struct SidecarManager {
     stdin_writer: Arc<Mutex<Option<Box<dyn Write + Send>>>>,
     ready: Arc<Mutex<bool>>,
     sink: Arc<dyn EventSink>,
-    config: SidecarConfig,
+    config: Mutex<SidecarConfig>,
 }
 
 impl SidecarManager {
@@ -68,17 +73,23 @@ impl SidecarManager {
             stdin_writer: Arc::new(Mutex::new(None)),
             ready: Arc::new(Mutex::new(false)),
             sink,
-            config,
+            config: Mutex::new(config),
         }
     }
 
+    /// Update the sandbox configuration. Takes effect on next sidecar (re)start.
+    pub fn set_sandbox(&self, sandbox: SandboxConfig) {
+        self.config.lock().unwrap().sandbox = sandbox;
+    }
+
     pub fn start(&self) -> Result<(), String> {
         let mut child_lock = self.child.lock().unwrap();
         if child_lock.is_some() {
             return Err("Sidecar already running".to_string());
         }
 
-        let cmd = self.resolve_sidecar_command()?;
+        let config = self.config.lock().unwrap();
+        let cmd = self.resolve_sidecar_command_with_config(&config)?;
 
         log::info!("Starting sidecar: {} {}", cmd.program, cmd.args.join(" "));
 
@@ -92,14 +103,36 @@ impl SidecarManager {
             })
             .collect();
 
-        let mut child = Command::new(&cmd.program)
+        let mut command = Command::new(&cmd.program);
+        command
             .args(&cmd.args)
             .env_clear()
             .envs(clean_env)
-            .envs(self.config.env_overrides.iter().map(|(k, v)| (k.as_str(), v.as_str())))
+            .envs(config.env_overrides.iter().map(|(k, v)| (k.as_str(), v.as_str())))
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
-            .stderr(Stdio::piped())
+            .stderr(Stdio::piped());
+
+        // Apply Landlock sandbox in child process before exec (Linux only).
+        // Restrictions are inherited by all child processes (provider CLIs).
+        #[cfg(unix)]
+        if config.sandbox.enabled {
+            let sandbox = config.sandbox.clone();
+            unsafe {
+                command.pre_exec(move || {
+                    sandbox.apply().map(|enforced| {
+                        if !enforced {
+                            log::warn!("Landlock sandbox not enforced in sidecar child");
+                        }
+                    }).map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))
+                });
+            }
+        }
+
+        // Drop config lock before spawn (pre_exec closure owns the sandbox clone)
+        drop(config);
+
+        let mut child = command
             .spawn()
             .map_err(|e| format!("Failed to start sidecar: {e}"))?;
 
@@ -197,11 +230,12 @@ impl SidecarManager {
 
         // Validate that the requested provider has a runner available
         let runner_name = format!("{}-runner.mjs", options.provider);
-        let runner_exists = self
-            .config
+        let config = self.config.lock().unwrap();
+        let runner_exists = config
             .search_paths
             .iter()
             .any(|base| base.join("dist").join(&runner_name).exists());
+        drop(config);
         if !runner_exists {
             return Err(format!(
                 "No sidecar runner found for provider '{}' (expected {})",
@@ -265,12 +299,12 @@ impl SidecarManager {
 
     /// Resolve a sidecar runner command. Uses the default claude-runner for startup.
     /// Future providers will have their own runners (e.g. codex-runner.mjs).
-    fn resolve_sidecar_command(&self) -> Result<SidecarCommand, String> {
-        self.resolve_sidecar_for_provider("claude")
+    fn resolve_sidecar_command_with_config(&self, config: &SidecarConfig) -> Result<SidecarCommand, String> {
+        Self::resolve_sidecar_for_provider_with_config(config, "claude")
     }
 
     /// Resolve a sidecar command for a specific provider's runner file.
-    fn resolve_sidecar_for_provider(&self, provider: &str) -> Result<SidecarCommand, String> {
+    fn resolve_sidecar_for_provider_with_config(config: &SidecarConfig, provider: &str) -> Result<SidecarCommand, String> {
         let runner_name = format!("{}-runner.mjs", provider);
 
         // Try Deno first (faster startup, better perf), fall back to Node.js.
@@ -289,7 +323,7 @@ impl SidecarManager {
 
         let mut checked = Vec::new();
 
-        for base in &self.config.search_paths {
+        for base in &config.search_paths {
             let mjs_path = base.join("dist").join(&runner_name);
             if mjs_path.exists() {
                 if has_deno {

v2/bterminal-relay/src/main.rs

@@ -99,6 +99,7 @@ async fn main() {
     let sidecar_config = SidecarConfig {
         search_paths,
         env_overrides: std::collections::HashMap::new(),
+        sandbox: Default::default(),
     };
     let token = Arc::new(cli.token);
 

v2/src-tauri/src/commands/agent.rs

@@ -1,6 +1,7 @@
 use tauri::State;
 use crate::AppState;
 use crate::sidecar::AgentQueryOptions;
+use bterminal_core::sandbox::SandboxConfig;
 
 #[tauri::command]
 #[tracing::instrument(skip(state, options), fields(session_id = %options.session_id))]
@@ -27,3 +28,31 @@ pub fn agent_ready(state: State<'_, AppState>) -> bool {
 pub fn agent_restart(state: State<'_, AppState>) -> Result<(), String> {
     state.sidecar_manager.restart()
 }
+
+/// Update sidecar sandbox configuration and restart to apply.
+/// `project_cwds` — directories needing read+write access.
+/// `worktree_roots` — optional worktree directories.
+/// `enabled` — whether Landlock sandboxing is active.
+#[tauri::command]
+#[tracing::instrument(skip(state))]
+pub fn agent_set_sandbox(
+    state: State<'_, AppState>,
+    project_cwds: Vec<String>,
+    worktree_roots: Vec<String>,
+    enabled: bool,
+) -> Result<(), String> {
+    let cwd_refs: Vec<&str> = project_cwds.iter().map(|s| s.as_str()).collect();
+    let wt_refs: Vec<&str> = worktree_roots.iter().map(|s| s.as_str()).collect();
+
+    let mut sandbox = SandboxConfig::for_projects(&cwd_refs, &wt_refs);
+    sandbox.enabled = enabled;
+
+    state.sidecar_manager.set_sandbox(sandbox);
+
+    // Restart sidecar so Landlock restrictions take effect on the new process
+    if state.sidecar_manager.is_ready() {
+        state.sidecar_manager.restart()?;
+    }
+
+    Ok(())
+}

v2/src/lib/adapters/agent-bridge.ts

@@ -51,6 +51,15 @@ export async function restartAgent(): Promise<void> {
   return invoke('agent_restart');
 }
 
+/** Update Landlock sandbox config and restart sidecar to apply. */
+export async function setSandbox(
+  projectCwds: string[],
+  worktreeRoots: string[],
+  enabled: boolean,
+): Promise<void> {
+  return invoke('agent_set_sandbox', { projectCwds, worktreeRoots, enabled });
+}
+
 export interface SidecarMessage {
   type: string;
   sessionId?: string;

v2/src/lib/types/groups.ts

@@ -16,6 +16,8 @@ export interface ProjectConfig {
   provider?: ProviderId;
   /** When true, agents for this project use git worktrees for isolation */
   useWorktrees?: boolean;
+  /** When true, sidecar process is sandboxed via Landlock (Linux 5.13+, restricts filesystem access) */
+  sandboxEnabled?: boolean;
   /** Anchor token budget scale (defaults to 'medium' = 6K tokens) */
   anchorBudgetScale?: AnchorBudgetScale;
   /** Stall detection threshold in minutes (defaults to 15) */