Implement config file parsing and precedence with CLI

Cargo.lock

@@ -8,7 +8,9 @@ version = "0.1.0"
 dependencies = [
  "clap",
  "glob",
+ "serde",
  "tempfile",
+ "toml",
 ]
 
 [[package]]
@@ -325,6 +327,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a8e94ea7f378bd32cbbd37198a4a91436180c5bb472411e48b5ec2e2124ae9e"
 dependencies = [
  "serde_core",
+ "serde_derive",
 ]
 
 [[package]]
@@ -360,6 +363,15 @@ dependencies = [
  "zmij",
 ]
 
+[[package]]
+name = "serde_spanned"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "876ac351060d4f882bb1032b6369eb0aef79ad9df1ea8bc404874d8cc3d0cd98"
+dependencies = [
+ "serde_core",
+]
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -390,6 +402,45 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "toml"
+version = "1.1.0+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8195ca05e4eb728f4ba94f3e3291661320af739c4e43779cbdfae82ab239fcc"
+dependencies = [
+ "indexmap",
+ "serde_core",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_parser",
+ "toml_writer",
+ "winnow",
+]
+
+[[package]]
+name = "toml_datetime"
+version = "1.1.0+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97251a7c317e03ad83774a8752a7e81fb6067740609f75ea2b585b569a59198f"
+dependencies = [
+ "serde_core",
+]
+
+[[package]]
+name = "toml_parser"
+version = "1.1.0+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2334f11ee363607eb04df9b8fc8a13ca1715a72ba8662a26ac285c98aabb4011"
+dependencies = [
+ "winnow",
+]
+
+[[package]]
+name = "toml_writer"
+version = "1.1.0+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d282ade6016312faf3e41e57ebbba0c073e4056dab1232ab1cb624199648f8ed"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"
@@ -475,6 +526,12 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "winnow"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09dac053f1cd375980747450bfc7250c264eaae0583872e845c0c7cd578872b5"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"

Cargo.toml

@@ -14,6 +14,8 @@ path = "src/main.rs"
 [dependencies]
 clap = { version = "4", features = ["derive"] }
 glob = "0.3"
+serde = { version = "1", features = ["derive"] }
+toml = "1"
 
 [dev-dependencies]
 tempfile = "3"

src/cli.rs

@@ -0,0 +1,60 @@
+use std::ffi::OsString;
+use std::path::PathBuf;
+
+use clap::Parser;
+
+#[derive(Parser, Debug, Default)]
+#[command(
+    name = "agent-sandbox",
+    version,
+    about = "Sandbox agentic coding assistants with bubblewrap"
+)]
+pub struct Args {
+    /// Blacklist mode: bind / read-only, overlay sensitive paths (default)
+    #[arg(long, conflicts_with = "whitelist")]
+    pub blacklist: bool,
+
+    /// Whitelist mode: only explicitly listed minimal paths visible
+    #[arg(long)]
+    pub whitelist: bool,
+
+    /// Harden: unshare IPC, PID, UTS; private /tmp, /dev, /run
+    #[arg(long)]
+    pub hardened: bool,
+
+    /// Unshare the network namespace
+    #[arg(long)]
+    pub no_net: bool,
+
+    /// Bind an extra path read-write (repeatable)
+    #[arg(long = "rw", value_name = "PATH", action = clap::ArgAction::Append)]
+    pub extra_rw: Vec<PathBuf>,
+
+    /// Bind an extra path read-only (repeatable)
+    #[arg(long = "ro", value_name = "PATH", action = clap::ArgAction::Append)]
+    pub extra_ro: Vec<PathBuf>,
+
+    /// Print the bwrap command without executing
+    #[arg(long)]
+    pub dry_run: bool,
+
+    /// Working directory inside the sandbox (default: current directory)
+    #[arg(long, value_name = "PATH")]
+    pub chdir: Option<PathBuf>,
+
+    /// Use a named profile from the config file
+    #[arg(long, conflicts_with = "no_config")]
+    pub profile: Option<String>,
+
+    /// Path to config file (default: $XDG_CONFIG_HOME/agent-sandbox/config.toml)
+    #[arg(long = "config", value_name = "PATH")]
+    pub config_path: Option<PathBuf>,
+
+    /// Skip loading the config file entirely
+    #[arg(long)]
+    pub no_config: bool,
+
+    /// Command and arguments to run inside the sandbox
+    #[arg(trailing_var_arg = true, allow_hyphen_values = true)]
+    pub command_and_args: Vec<OsString>,
+}

src/config.rs

@@ -0,0 +1,544 @@
+use std::collections::HashMap;
+use std::ffi::OsString;
+use std::path::{Path, PathBuf};
+
+use serde::Deserialize;
+
+use crate::cli::Args;
+use crate::{SandboxConfig, SandboxError, SandboxMode};
+
+pub fn build(args: Args, file_config: Option<FileConfig>) -> Result<SandboxConfig, SandboxError> {
+    let (mut globals, mut profile) = match file_config {
+        Some(c) => {
+            let profile = c.resolve_profile(args.profile.as_deref())?;
+            (c.options, profile)
+        }
+        None => (Options::default(), Options::default()),
+    };
+
+    validate_mode(&globals)?;
+    validate_mode(&profile)?;
+    globals.validate_paths()?;
+    profile.validate_paths()?;
+
+    let (command, command_args) = resolve_command(
+        args.command_and_args,
+        profile.command.clone(),
+        globals.command.clone(),
+    );
+    let command = resolve_binary(&command)
+        .ok_or_else(|| SandboxError::CommandNotFound(PathBuf::from(&command)))?;
+
+    Ok(SandboxConfig {
+        mode: merge_mode(args.blacklist, args.whitelist, &profile, &globals),
+        hardened: merge_flag(args.hardened, profile.hardened, globals.hardened),
+        no_net: merge_flag(args.no_net, profile.no_net, globals.no_net),
+        dry_run: merge_flag(args.dry_run, profile.dry_run, globals.dry_run),
+        chdir: resolve_chdir(args.chdir, profile.chdir, globals.chdir)?,
+        extra_rw: merge_paths(args.extra_rw, &profile.rw, &globals.rw)?,
+        extra_ro: merge_paths(args.extra_ro, &profile.ro, &globals.ro)?,
+        command,
+        command_args,
+    })
+}
+
+fn merge_mode(
+    cli_blacklist: bool,
+    cli_whitelist: bool,
+    profile: &Options,
+    globals: &Options,
+) -> SandboxMode {
+    if cli_whitelist {
+        return SandboxMode::Whitelist;
+    }
+    if cli_blacklist {
+        return SandboxMode::Blacklist;
+    }
+    resolve_mode(profile)
+        .or_else(|| resolve_mode(globals))
+        .unwrap_or(SandboxMode::Blacklist)
+}
+
+fn resolve_mode(opts: &Options) -> Option<SandboxMode> {
+    match (opts.blacklist, opts.whitelist) {
+        (_, Some(true)) => Some(SandboxMode::Whitelist),
+        (Some(true), _) => Some(SandboxMode::Blacklist),
+        _ => None,
+    }
+}
+
+fn merge_flag(cli: bool, profile: Option<bool>, globals: Option<bool>) -> bool {
+    if cli {
+        return true;
+    }
+    profile.or(globals).unwrap_or(false)
+}
+
+fn resolve_chdir(
+    cli: Option<PathBuf>,
+    profile: Option<PathBuf>,
+    globals: Option<PathBuf>,
+) -> Result<PathBuf, SandboxError> {
+    match cli.or(profile).or(globals) {
+        Some(p) => std::fs::canonicalize(&p).map_err(|_| SandboxError::ChdirMissing(p)),
+        None => std::env::current_dir().map_err(SandboxError::CurrentDirUnavailable),
+    }
+}
+
+fn merge_paths(
+    cli: Vec<PathBuf>,
+    profile: &[PathBuf],
+    globals: &[PathBuf],
+) -> Result<Vec<PathBuf>, SandboxError> {
+    let config_paths = globals.iter().chain(profile).cloned();
+    let cli_paths = cli
+        .into_iter()
+        .map(|p| std::fs::canonicalize(&p).map_err(|_| SandboxError::PathMissing(p)))
+        .collect::<Result<Vec<_>, _>>()?;
+    Ok(config_paths.chain(cli_paths).collect())
+}
+
+fn resolve_command(
+    mut positional: Vec<OsString>,
+    profile_cmd: Option<CommandValue>,
+    globals_cmd: Option<CommandValue>,
+) -> (OsString, Vec<OsString>) {
+    if !positional.is_empty() {
+        let cmd = positional.remove(0);
+        return (cmd, positional);
+    }
+    if let Some(config_cmd) = profile_cmd.or(globals_cmd) {
+        let parts = config_cmd.into_vec();
+        let cmd = OsString::from(&parts[0]);
+        let args = parts[1..].iter().map(OsString::from).collect();
+        return (cmd, args);
+    }
+    if let Ok(cmd) = std::env::var("SANDBOX_CMD") {
+        return (OsString::from(cmd), vec![]);
+    }
+    (
+        OsString::from("claude"),
+        vec![OsString::from("--dangerously-skip-permissions")],
+    )
+}
+
+fn resolve_binary(name: &OsString) -> Option<PathBuf> {
+    let path = PathBuf::from(name);
+    if path.is_absolute() || path.components().count() > 1 {
+        return path.is_file().then_some(path);
+    }
+    std::env::var_os("PATH").and_then(|path_var| {
+        std::env::split_paths(&path_var)
+            .map(|dir| dir.join(name))
+            .find(|p| p.is_file())
+    })
+}
+
+#[derive(Deserialize, Default)]
+pub struct FileConfig {
+    #[serde(flatten)]
+    pub options: Options,
+    #[serde(default)]
+    pub profile: HashMap<String, Options>,
+}
+
+impl FileConfig {
+    pub fn load(path: &Path) -> Result<Self, SandboxError> {
+        let contents = std::fs::read_to_string(path).map_err(|e| SandboxError::ConfigRead {
+            path: path.to_path_buf(),
+            source: e,
+        })?;
+        toml::from_str(&contents).map_err(|e| SandboxError::ConfigParse {
+            path: path.to_path_buf(),
+            source: e,
+        })
+    }
+
+    fn resolve_profile(&self, name: Option<&str>) -> Result<Options, SandboxError> {
+        match name {
+            Some(n) => self
+                .profile
+                .get(n)
+                .cloned()
+                .ok_or_else(|| SandboxError::ProfileNotFound(n.to_string())),
+            None => Ok(Options::default()),
+        }
+    }
+}
+
+#[derive(Deserialize, Default, Clone)]
+#[serde(rename_all = "kebab-case")]
+pub struct Options {
+    pub blacklist: Option<bool>,
+    pub whitelist: Option<bool>,
+    pub hardened: Option<bool>,
+    pub no_net: Option<bool>,
+    pub command: Option<CommandValue>,
+    pub dry_run: Option<bool>,
+    pub chdir: Option<PathBuf>,
+    #[serde(default)]
+    pub rw: Vec<PathBuf>,
+    #[serde(default)]
+    pub ro: Vec<PathBuf>,
+}
+
+impl Options {
+    fn validate_paths(&mut self) -> Result<(), SandboxError> {
+        for p in &mut self.rw {
+            *p = expand_and_canonicalize(p)?;
+        }
+        for p in &mut self.ro {
+            *p = expand_and_canonicalize(p)?;
+        }
+        if let Some(ref chdir) = self.chdir {
+            self.chdir = Some(expand_and_canonicalize(chdir)?);
+        }
+        Ok(())
+    }
+}
+
+#[derive(Deserialize, Clone)]
+#[serde(untagged)]
+pub enum CommandValue {
+    Simple(String),
+    WithArgs(Vec<String>),
+}
+
+impl CommandValue {
+    pub fn into_vec(self) -> Vec<String> {
+        match self {
+            Self::Simple(s) => vec![s],
+            Self::WithArgs(v) => v,
+        }
+    }
+}
+
+pub fn find_config_path(explicit: Option<&Path>) -> Option<PathBuf> {
+    if let Some(p) = explicit {
+        return Some(p.to_path_buf());
+    }
+    let config_dir = std::env::var("XDG_CONFIG_HOME")
+        .ok()
+        .filter(|s| !s.is_empty())
+        .map(PathBuf::from)
+        .or_else(|| {
+            std::env::var("HOME")
+                .ok()
+                .filter(|s| !s.is_empty())
+                .map(|h| PathBuf::from(h).join(".config"))
+        })?;
+    let path = config_dir.join("agent-sandbox/config.toml");
+    path.exists().then_some(path)
+}
+
+fn validate_mode(opts: &Options) -> Result<(), SandboxError> {
+    if opts.blacklist == Some(true) && opts.whitelist == Some(true) {
+        return Err(SandboxError::ConflictingMode);
+    }
+    Ok(())
+}
+
+fn expand_tilde(path: &Path) -> Result<PathBuf, SandboxError> {
+    let s = path.to_string_lossy();
+    if !s.starts_with('~') {
+        return Ok(path.to_path_buf());
+    }
+    if s.len() > 1 && !s.starts_with("~/") {
+        return Err(SandboxError::ConfigPathNotAbsolute(path.to_path_buf()));
+    }
+    let home = std::env::var("HOME")
+        .ok()
+        .filter(|h| !h.is_empty())
+        .ok_or(SandboxError::HomeNotSet)?;
+    Ok(PathBuf::from(home).join(s.strip_prefix("~/").unwrap_or("")))
+}
+
+fn require_absolute(path: &Path) -> Result<(), SandboxError> {
+    if !path.is_absolute() {
+        return Err(SandboxError::ConfigPathNotAbsolute(path.to_path_buf()));
+    }
+    Ok(())
+}
+
+fn expand_and_canonicalize(path: &Path) -> Result<PathBuf, SandboxError> {
+    let expanded = expand_tilde(path)?;
+    require_absolute(&expanded)?;
+    std::fs::canonicalize(&expanded).map_err(|e| SandboxError::ConfigRead {
+        path: expanded,
+        source: e,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::LazyLock;
+
+    use super::*;
+
+    const FULL_CONFIG_TOML: &str = r#"
+        hardened = true
+        no-net = true
+        rw = ["/tmp/a", "/tmp/b"]
+        command = "zsh"
+
+        [profile.claude]
+        rw = ["/home/user/.config/claude"]
+        ro = ["/etc/claude", "/etc/shared"]
+        command = ["bash", "-c", "echo hi"]
+
+        [profile.codex]
+        whitelist = true
+        dry-run = true
+        chdir = "/home/user/project"
+        rw = ["/home/user/.codex"]
+    "#;
+
+    static CONFIG: LazyLock<FileConfig> =
+        LazyLock::new(|| toml::from_str(FULL_CONFIG_TOML).unwrap());
+
+    #[test]
+    fn globals_scalars() {
+        assert_eq!(CONFIG.options.hardened, Some(true));
+        assert_eq!(CONFIG.options.no_net, Some(true));
+    }
+
+    #[test]
+    fn globals_multi_element_vecs() {
+        assert_paths(&CONFIG.options.rw, &["/tmp/a", "/tmp/b"]);
+    }
+
+    #[test]
+    fn globals_simple_command() {
+        assert_command(&CONFIG.options.command, &["zsh"]);
+    }
+
+    #[test]
+    fn unset_vecs_default_empty() {
+        assert!(CONFIG.options.ro.is_empty());
+    }
+
+    #[test]
+    fn unset_scalars_are_none() {
+        assert_eq!(CONFIG.profile["claude"].hardened, None);
+    }
+
+    #[test]
+    fn profile_multi_element_vecs() {
+        assert_paths(
+            &CONFIG.profile["claude"].ro,
+            &["/etc/claude", "/etc/shared"],
+        );
+    }
+
+    #[test]
+    fn profile_command_with_args() {
+        assert_command(
+            &CONFIG.profile["claude"].command,
+            &["bash", "-c", "echo hi"],
+        );
+    }
+
+    #[test]
+    fn profile_kebab_case_scalars() {
+        let codex = &CONFIG.profile["codex"];
+        assert_eq!(codex.whitelist, Some(true));
+        assert_eq!(codex.dry_run, Some(true));
+        assert_eq!(codex.chdir, Some(PathBuf::from("/home/user/project")));
+    }
+
+    fn args_with_command() -> Args {
+        Args {
+            command_and_args: vec!["/usr/bin/true".into()],
+            ..Args::default()
+        }
+    }
+
+    #[test]
+    fn build_hardened_from_globals() {
+        let file_config = FileConfig {
+            options: Options {
+                hardened: Some(true),
+                ..Options::default()
+            },
+            ..FileConfig::default()
+        };
+        let config = build(args_with_command(), Some(file_config)).unwrap();
+        assert!(config.hardened);
+    }
+
+    #[test]
+    fn build_profile_overrides_globals() {
+        let file_config = FileConfig {
+            options: Options {
+                hardened: Some(true),
+                ..Options::default()
+            },
+            profile: HashMap::from([(
+                "relaxed".into(),
+                Options {
+                    hardened: Some(false),
+                    ..Options::default()
+                },
+            )]),
+        };
+        let args = Args {
+            profile: Some("relaxed".into()),
+            ..args_with_command()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert!(!config.hardened);
+    }
+
+    #[test]
+    fn build_cli_flag_overrides_profile() {
+        let file_config = FileConfig {
+            profile: HashMap::from([(
+                "nonet".into(),
+                Options {
+                    no_net: Some(false),
+                    ..Options::default()
+                },
+            )]),
+            ..FileConfig::default()
+        };
+        let args = Args {
+            profile: Some("nonet".into()),
+            no_net: true,
+            ..args_with_command()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert!(config.no_net);
+    }
+
+    #[test]
+    fn build_cli_mode_overrides_profile() {
+        let file_config = FileConfig {
+            profile: HashMap::from([(
+                "wl".into(),
+                Options {
+                    whitelist: Some(true),
+                    ..Options::default()
+                },
+            )]),
+            ..FileConfig::default()
+        };
+        let args = Args {
+            profile: Some("wl".into()),
+            blacklist: true,
+            ..args_with_command()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert!(matches!(config.mode, SandboxMode::Blacklist));
+    }
+
+    #[test]
+    fn build_rw_paths_accumulate() {
+        let file_config = FileConfig {
+            options: Options {
+                rw: vec![PathBuf::from("/tmp")],
+                ..Options::default()
+            },
+            profile: HashMap::from([(
+                "extra".into(),
+                Options {
+                    rw: vec![PathBuf::from("/usr")],
+                    ..Options::default()
+                },
+            )]),
+        };
+        let args = Args {
+            profile: Some("extra".into()),
+            extra_rw: vec![PathBuf::from("/var")],
+            ..args_with_command()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert_eq!(config.extra_rw.len(), 3);
+    }
+
+    #[test]
+    fn build_command_from_profile() {
+        let file_config = FileConfig {
+            profile: HashMap::from([(
+                "test".into(),
+                Options {
+                    command: Some(CommandValue::WithArgs(vec![
+                        "/usr/bin/true".into(),
+                        "--flag".into(),
+                    ])),
+                    ..Options::default()
+                },
+            )]),
+            ..FileConfig::default()
+        };
+        let args = Args {
+            profile: Some("test".into()),
+            ..Args::default()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert_eq!(config.command, PathBuf::from("/usr/bin/true"));
+        assert_eq!(config.command_args, vec![OsString::from("--flag")]);
+    }
+
+    #[test]
+    fn build_cli_command_overrides_config() {
+        let file_config = FileConfig {
+            options: Options {
+                command: Some(CommandValue::Simple("/usr/bin/false".into())),
+                ..Options::default()
+            },
+            ..FileConfig::default()
+        };
+        let args = Args {
+            command_and_args: vec!["/usr/bin/true".into()],
+            ..Args::default()
+        };
+        let config = build(args, Some(file_config)).unwrap();
+        assert_eq!(config.command, PathBuf::from("/usr/bin/true"));
+    }
+
+    #[test]
+    fn build_no_file_config() {
+        let config = build(args_with_command(), None).unwrap();
+        assert!(matches!(config.mode, SandboxMode::Blacklist));
+        assert!(!config.hardened);
+    }
+
+    #[test]
+    fn build_missing_profile_errors() {
+        let args = Args {
+            profile: Some("nope".into()),
+            ..args_with_command()
+        };
+        assert!(matches!(
+            build(args, Some(FileConfig::default())),
+            Err(SandboxError::ProfileNotFound(_))
+        ));
+    }
+
+    #[test]
+    fn build_conflicting_mode_errors() {
+        let file_config = FileConfig {
+            options: Options {
+                blacklist: Some(true),
+                whitelist: Some(true),
+                ..Options::default()
+            },
+            ..FileConfig::default()
+        };
+        assert!(matches!(
+            build(args_with_command(), Some(file_config)),
+            Err(SandboxError::ConflictingMode)
+        ));
+    }
+
+    fn assert_paths(actual: &[PathBuf], expected: &[&str]) {
+        let expected: Vec<PathBuf> = expected.iter().map(PathBuf::from).collect();
+        assert_eq!(actual, &expected);
+    }
+
+    fn assert_command(cmd: &Option<CommandValue>, expected: &[&str]) {
+        let actual = cmd.clone().unwrap().into_vec();
+        let expected: Vec<String> = expected.iter().map(|s| s.to_string()).collect();
+        assert_eq!(actual, expected);
+    }
+}

src/errors.rs

@@ -7,12 +7,22 @@ pub enum SandboxError {
     BwrapNotFound,
     CommandNotFound(PathBuf),
     CommandNotExecutable(PathBuf),
-    RwPathMissing(PathBuf),
+    PathMissing(PathBuf),
-    RoPathMissing(PathBuf),
     ChdirMissing(PathBuf),
     CurrentDirUnavailable(std::io::Error),
     GlobPattern(glob::PatternError),
     Io(std::io::Error),
+    ConfigRead {
+        path: PathBuf,
+        source: std::io::Error,
+    },
+    ConfigParse {
+        path: PathBuf,
+        source: toml::de::Error,
+    },
+    ProfileNotFound(String),
+    ConflictingMode,
+    ConfigPathNotAbsolute(PathBuf),
 }
 
 impl std::fmt::Display for SandboxError {
@@ -34,12 +44,25 @@ impl std::fmt::Display for SandboxError {
             Self::CommandNotExecutable(p) => {
                 write!(f, "command is not executable: {}", p.display())
             }
-            Self::RwPathMissing(p) => write!(f, "--rw path does not exist: {}", p.display()),
+            Self::PathMissing(p) => write!(f, "path does not exist: {}", p.display()),
-            Self::RoPathMissing(p) => write!(f, "--ro path does not exist: {}", p.display()),
             Self::ChdirMissing(p) => write!(f, "--chdir path does not exist: {}", p.display()),
             Self::CurrentDirUnavailable(e) => write!(f, "cannot determine current directory: {e}"),
             Self::GlobPattern(e) => write!(f, "invalid glob pattern: {e}"),
             Self::Io(e) => write!(f, "I/O error: {e}"),
+            Self::ConfigRead { path, source } => {
+                write!(f, "cannot read config file '{}': {source}", path.display())
+            }
+            Self::ConfigParse { path, source } => {
+                write!(f, "cannot parse config file '{}': {source}", path.display())
+            }
+            Self::ProfileNotFound(name) => write!(f, "profile not found in config: {name}"),
+            Self::ConflictingMode => write!(
+                f,
+                "config section sets both blacklist and whitelist to true"
+            ),
+            Self::ConfigPathNotAbsolute(p) => {
+                write!(f, "config path is not absolute: {}", p.display())
+            }
         }
     }
 }
@@ -50,6 +73,8 @@ impl std::error::Error for SandboxError {
             Self::CurrentDirUnavailable(e) => Some(e),
             Self::GlobPattern(e) => Some(e),
             Self::Io(e) => Some(e),
+            Self::ConfigRead { source, .. } => Some(source),
+            Self::ConfigParse { source, .. } => Some(source),
             _ => None,
         }
     }

src/lib.rs

@@ -1,5 +1,7 @@
 mod agents;
 mod blacklist;
+pub mod cli;
+pub mod config;
 mod errors;
 mod preflight;
 mod sandbox;

src/main.rs

@@ -1,146 +1,28 @@
-use std::ffi::{OsStr, OsString};
-use std::path::{Path, PathBuf};
 use std::process;
 
 use clap::Parser;
 
-use agent_sandbox::{SandboxConfig, SandboxMode};
+use agent_sandbox::cli::Args;
-
+use agent_sandbox::config::{self, FileConfig};
-#[derive(Parser, Debug)]
-#[command(
-    name = "agent-sandbox",
-    version,
-    about = "Sandbox agentic coding assistants with bubblewrap"
-)]
-struct Args {
-    /// Blacklist mode: bind / read-only, overlay sensitive paths (default)
-    #[arg(long, conflicts_with = "whitelist")]
-    blacklist: bool,
-
-    /// Whitelist mode: only explicitly listed minimal paths visible
-    #[arg(long)]
-    whitelist: bool,
-
-    /// Harden: unshare IPC, PID, UTS; private /tmp, /dev, /run
-    #[arg(long)]
-    hardened: bool,
-
-    /// Unshare the network namespace
-    #[arg(long)]
-    no_net: bool,
-
-    /// Bind an extra path read-write (repeatable)
-    #[arg(long = "rw", value_name = "PATH", action = clap::ArgAction::Append)]
-    extra_rw: Vec<PathBuf>,
-
-    /// Bind an extra path read-only (repeatable)
-    #[arg(long = "ro", value_name = "PATH", action = clap::ArgAction::Append)]
-    extra_ro: Vec<PathBuf>,
-
-    /// Print the bwrap command without executing
-    #[arg(long)]
-    dry_run: bool,
-
-    /// Working directory inside the sandbox (default: current directory)
-    #[arg(long, value_name = "PATH")]
-    chdir: Option<PathBuf>,
-
-    /// Command and arguments to run inside the sandbox
-    #[arg(trailing_var_arg = true, allow_hyphen_values = true)]
-    command_and_args: Vec<OsString>,
-}
 
 fn main() {
     let args = Args::parse();
 
-    let (command, command_args) = resolve_command(args.command_and_args);
+    let file_config = if args.no_config {
-    let command = assert_binary_exists(&command);
+        None
-    let chdir = assert_chdir(args.chdir);
-
-    let mode = if args.whitelist {
-        SandboxMode::Whitelist
     } else {
-        SandboxMode::Blacklist
+        config::find_config_path(args.config_path.as_deref())
+            .map(|p| FileConfig::load(&p).unwrap_or_else(|e| exit_err(&e)))
     };
 
-    let config = SandboxConfig {
+    let config = config::build(args, file_config).unwrap_or_else(|e| exit_err(&e));
-        mode,
-        hardened: args.hardened,
-        no_net: args.no_net,
-        extra_rw: args
-            .extra_rw
-            .iter()
-            .map(|p| canonicalize_or_exit(p))
-            .collect(),
-        extra_ro: args
-            .extra_ro
-            .iter()
-            .map(|p| canonicalize_or_exit(p))
-            .collect(),
-        command,
-        command_args,
-        chdir,
-        dry_run: args.dry_run,
-    };
 
     if let Err(e) = agent_sandbox::run(config) {
+        exit_err(&e);
+    }
+}
+
+fn exit_err(e: &dyn std::fmt::Display) -> ! {
     eprintln!("error: {e}");
     process::exit(1);
-    }
-}
-
-fn resolve_command(mut positional: Vec<OsString>) -> (OsString, Vec<OsString>) {
-    if !positional.is_empty() {
-        let cmd = positional.remove(0);
-        return (cmd, positional);
-    }
-    if let Ok(cmd) = std::env::var("SANDBOX_CMD") {
-        return (OsString::from(cmd), vec![]);
-    }
-    (
-        OsString::from("claude"),
-        vec![OsString::from("--dangerously-skip-permissions")],
-    )
-}
-
-fn assert_binary_exists(name: &OsStr) -> PathBuf {
-    resolve_binary(name).unwrap_or_else(|| {
-        eprintln!("error: command not found: {}", name.to_string_lossy());
-        process::exit(1);
-    })
-}
-
-fn assert_chdir(explicit: Option<PathBuf>) -> PathBuf {
-    if let Some(p) = explicit {
-        return canonicalize_or_exit(&p);
-    }
-    match std::env::current_dir() {
-        Ok(p) => p,
-        Err(e) => {
-            eprintln!(
-                "error: {}",
-                agent_sandbox::SandboxError::CurrentDirUnavailable(e)
-            );
-            process::exit(1);
-        }
-    }
-}
-
-fn canonicalize_or_exit(p: &Path) -> PathBuf {
-    std::fs::canonicalize(p).unwrap_or_else(|e| {
-        eprintln!("error: cannot resolve path '{}': {e}", p.display());
-        process::exit(1);
-    })
-}
-
-fn resolve_binary(name: &OsStr) -> Option<PathBuf> {
-    let path = PathBuf::from(name);
-    if path.is_absolute() || path.components().count() > 1 {
-        return path.is_file().then_some(path);
-    }
-    std::env::var_os("PATH").and_then(|path_var| {
-        std::env::split_paths(&path_var)
-            .map(|dir| dir.join(name))
-            .find(|p| p.is_file())
-    })
 }

src/sandbox.rs

@@ -167,7 +167,7 @@ fn ro_bind_under_tmpfs(cmd: &mut Command, base: &str, paths: &[&str]) {
 
 fn add_rw_bind(cmd: &mut Command, path: &Path) -> Result<(), SandboxError> {
     if !path.exists() {
-        return Err(SandboxError::RwPathMissing(path.to_path_buf()));
+        return Err(SandboxError::PathMissing(path.to_path_buf()));
     }
     cmd.arg("--bind").arg(path).arg(path);
     Ok(())
@@ -175,7 +175,7 @@ fn add_rw_bind(cmd: &mut Command, path: &Path) -> Result<(), SandboxError> {
 
 fn add_ro_bind(cmd: &mut Command, path: &Path) -> Result<(), SandboxError> {
     if !path.exists() {
-        return Err(SandboxError::RoPathMissing(path.to_path_buf()));
+        return Err(SandboxError::PathMissing(path.to_path_buf()));
     }
     cmd.arg("--ro-bind").arg(path).arg(path);
     Ok(())

tests/integration.rs

@@ -9,6 +9,12 @@ fn sandbox(extra_args: &[&str]) -> Command {
     cmd
 }
 
+fn write_config(dir: &TempDir, content: &str) -> String {
+    let path = dir.path().join("config.toml");
+    fs::write(&path, content).expect("failed to write config");
+    path.to_str().unwrap().to_string()
+}
+
 fn read_sid_from_stat(stat: &str) -> u32 {
     stat.trim()
         .split_whitespace()
@@ -538,3 +544,36 @@ fn rw_missing_path_errors() {
         "expected path in error message, got: {stderr}"
     );
 }
+
+#[test]
+fn config_missing_file_errors() {
+    let output = sandbox(&["--config", "/nonexistent/config.toml"])
+        .args(["--", "true"])
+        .output()
+        .expect("failed to execute");
+
+    assert!(!output.status.success());
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("/nonexistent/config.toml"),
+        "expected config path in error, got: {stderr}"
+    );
+}
+
+#[test]
+fn config_invalid_toml_errors() {
+    let dir = TempDir::new().unwrap();
+    let cfg = write_config(&dir, "not valid {{{{ toml");
+
+    let output = sandbox(&["--config", &cfg])
+        .args(["--", "true"])
+        .output()
+        .expect("failed to execute");
+
+    assert!(!output.status.success());
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("cannot parse"),
+        "expected parse error, got: {stderr}"
+    );
+}