lazaret/crates/lazaret-runtime-supervisor/src/supervision.rs

use std::ffi::{OsStr, OsString};
use std::fs::File;
use std::io;
use std::os::fd::{AsFd, AsRawFd, OwnedFd};
use std::os::unix::fs::FileExt;
use std::path::PathBuf;
use std::time::{Duration, Instant};

use lazaret_core::codec::{decode, encode};
use lazaret_core::identity::{
    ConfigurationFingerprint, CoordinatorId, DerivedPolicyDigest, DomainId, GenerationId,
    MountIdentity, NamespaceIdentity, NetworkSidecarId,
};
use lazaret_core::network::CanonicalDerivedNetworkPolicy;
use lazaret_core::records::{
    HostProcessOwnershipSlot, NetworkReadinessAttestation, ProcessOwnershipCommitAck,
    StagedProcessOwnership,
};
use lazaret_linux::capability;
use lazaret_linux::filesystem::sealed_memfd;
use lazaret_linux::process::{
    ChildStandardIo, ParentEdge, ProcessOwnershipContext, RetainedProcess, TargetCommand,
    child_broker, current_process_identity,
};
use lazaret_state_anchor::{
    RuntimeStateAnchorAbsenceAuthority, RuntimeStateAnchorAuthority, RuntimeStateAnchorInherited,
    RuntimeStateAnchorMount, StateAnchorLaunchAuthority,
};
use rustix::event::{PollFd, PollFlags, Timespec, poll};
use rustix::fs::{MemfdFlags, memfd_create};
use rustix::io::{FdFlags, fcntl_setfd, read, write};
use rustix::process::Signal;
use rustix::thread::CapabilitySet;
use serde::{Deserialize, Serialize};

use crate::network::{
    NetworkAttestationContext, NetworkProbeRequest, PreparedNetwork,
    enter_generation_filesystem_namespaces, enter_generation_network_namespace, prepare_network,
    probe_current_network,
};
use crate::sandbox::RunscCommand;

const PRIVATE_ROLE_ARGUMENT: &str = "--lazaret-runtime-supervisor-role";
const MAX_CONTROL_MESSAGE: usize = 16 * 1024;
const READINESS_TIMEOUT: Duration = Duration::from_secs(30);
const TERMINATION_GRACE: Duration = Duration::from_secs(2);

#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub enum AttachedRunscSignal {
    Stop,
    Continue,
    Kill,
}

impl AttachedRunscSignal {
    const fn signal(self) -> Signal {
        match self {
            Self::Stop => Signal::STOP,
            Self::Continue => Signal::CONT,
            Self::Kill => Signal::KILL,
        }
    }
}

#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub enum SupervisorEvent {
    StateAnchorStaged(StagedProcessOwnership),
    StateAnchorReady {
        staged: StagedProcessOwnership,
        user_namespace: lazaret_core::identity::NamespaceIdentity,
        mount_namespace: lazaret_core::identity::NamespaceIdentity,
        mount: lazaret_core::identity::MountIdentity,
    },
    SidecarStarted,
    HelperStaged(StagedProcessOwnership),
    HelperReady(StagedProcessOwnership),
    NetworkAttestation(NetworkReadinessAttestation),
    NetworkProbe(lazaret_core::records::NetworkReachabilityProbe),
    HelperExited,
    Staged(StagedProcessOwnership),
    Ready {
        staged: StagedProcessOwnership,
        sentry_pid_inventory: u32,
    },
    SignalApplied(AttachedRunscSignal),
    SandboxStopped,
    SidecarStopped,
    StateAnchorUnmounted {
        mount: lazaret_core::identity::MountIdentity,
    },
    StateAnchorAbsenceObserved {
        user_namespace: NamespaceIdentity,
        mount_namespace: NamespaceIdentity,
        mount: MountIdentity,
        observed: MountIdentity,
    },
    Exited,
    AttachedRunscExited,
    Stopped,
    Refused(String),
}

#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
enum CoordinatorMessage {
    MountStateAnchor,
    StateAnchorStagedAck(ProcessOwnershipCommitAck),
    StartSidecar,
    HelperStagedAck(ProcessOwnershipCommitAck),
    NetworkAttestationAccepted(NetworkProbeRequest),
    NetworkReadinessCommitted,
    StagedAck(ProcessOwnershipCommitAck),
    SandboxCommitted,
    SignalAttachedRunsc(AttachedRunscSignal),
    StopSandbox,
    StopSidecar,
    UnmountStateAnchor,
    ObserveStateAnchorAbsence {
        user_namespace: NamespaceIdentity,
        mount_namespace: NamespaceIdentity,
        mount: MountIdentity,
    },
    Exit,
    Stop,
}

pub struct CoordinatorChannel {
    descriptor: OwnedFd,
}

impl CoordinatorChannel {
    #[must_use]
    pub const fn new(descriptor: OwnedFd) -> Self {
        Self { descriptor }
    }

    /// # Errors
    /// Returns an error for a closed, malformed, oversized, or unknown message.
    pub fn receive(&self) -> io::Result<SupervisorEvent> {
        receive_message(&self.descriptor)
    }

    /// # Errors
    /// Returns an error when exact State Anchor acquisition cannot be requested.
    pub fn mount_state_anchor(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::MountStateAnchor)
    }

    /// # Errors
    /// Returns an error when the exact daemon acknowledgment cannot be delivered.
    pub fn acknowledge_state_anchor(
        &self,
        acknowledgment: ProcessOwnershipCommitAck,
    ) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::StateAnchorStagedAck(acknowledgment),
        )
    }

    /// # Errors
    /// Returns an error when the RS-owned sidecar install path cannot be released.
    pub fn start_sidecar(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::StartSidecar)
    }

    /// # Errors
    /// Returns an error when the exact typed acknowledgment cannot be delivered.
    pub fn acknowledge_staged(&self, acknowledgment: ProcessOwnershipCommitAck) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::StagedAck(acknowledgment),
        )
    }

    /// # Errors
    /// Returns an error when the exact helper acknowledgment cannot be delivered.
    pub fn acknowledge_helper(&self, acknowledgment: ProcessOwnershipCommitAck) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::HelperStagedAck(acknowledgment),
        )
    }

    /// # Errors
    /// Returns an error when accepted attestation cannot release sandbox acquisition.
    pub fn acknowledge_network_attestation(&self, request: NetworkProbeRequest) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::NetworkAttestationAccepted(request),
        )
    }

    /// # Errors
    /// Returns an error when durable network readiness cannot release sandbox acquisition.
    pub fn acknowledge_network_readiness(&self) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::NetworkReadinessCommitted,
        )
    }

    /// # Errors
    /// Returns an error when the durable sandbox commit cannot be acknowledged.
    pub fn acknowledge_sandbox_committed(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::SandboxCommitted)
    }

    /// # Errors
    /// Returns an error when the exact retained-runsc action cannot be requested.
    pub fn signal_attached_runsc(&self, signal: AttachedRunscSignal) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::SignalAttachedRunsc(signal),
        )
    }

    /// # Errors
    /// Returns an error when ordered sandbox stop cannot be requested.
    pub fn stop(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::Stop)
    }

    /// # Errors
    /// Returns an error when ordered sandbox stop cannot be requested.
    pub fn stop_sandbox(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::StopSandbox)
    }

    /// # Errors
    /// Returns an error when ordered sidecar stop cannot be requested.
    pub fn stop_sidecar(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::StopSidecar)
    }

    /// # Errors
    /// Returns an error when exact State Anchor unmount cannot be requested.
    pub fn unmount_state_anchor(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::UnmountStateAnchor)
    }

    /// # Errors
    /// Returns an error when exact namespace-local absence observation cannot be requested.
    pub fn observe_state_anchor_absence(
        &self,
        user_namespace: NamespaceIdentity,
        mount_namespace: NamespaceIdentity,
        mount: MountIdentity,
    ) -> io::Result<()> {
        send_message(
            &self.descriptor,
            &CoordinatorMessage::ObserveStateAnchorAbsence {
                user_namespace,
                mount_namespace,
                mount,
            },
        )
    }

    /// # Errors
    /// Returns an error when graceful Runtime Supervisor exit cannot be requested.
    pub fn exit(&self) -> io::Result<()> {
        send_message(&self.descriptor, &CoordinatorMessage::Exit)
    }
}

pub struct RuntimeSupervisorLaunch {
    target: TargetCommand,
    ownership: ProcessOwnershipContext,
    policy_file: Option<File>,
    policy_digest: Option<DerivedPolicyDigest>,
    configuration_fingerprint: Option<ConfigurationFingerprint>,
    network_sidecar_id: Option<NetworkSidecarId>,
    runsc_command: RunscCommand,
    state_anchor: Option<StateAnchorLaunchAuthority>,
}

#[derive(Clone, Copy)]
pub struct RuntimeNetworkLaunch<'policy> {
    pub policy: &'policy CanonicalDerivedNetworkPolicy,
    pub configuration_fingerprint: ConfigurationFingerprint,
    pub network_sidecar_id: NetworkSidecarId,
}

impl RuntimeSupervisorLaunch {
    /// # Errors
    /// Refuses any command other than the deterministic foreground attached-runsc form.
    pub fn from_runsc_command(
        ownership: ProcessOwnershipContext,
        command: &RunscCommand,
    ) -> io::Result<Self> {
        if ownership.slot != HostProcessOwnershipSlot::SandboxRuntimeSupervisor
            || command.program() != OsStr::new("runsc")
            || !command
                .arguments()
                .iter()
                .any(|argument| argument == OsStr::new("run"))
            || command
                .arguments()
                .iter()
                .any(|argument| matches!(argument.to_str(), Some("-detach" | "--detach" | "-d")))
        {
            return Err(io::Error::other(
                "Runtime Supervisor requires foreground attached runsc",
            ));
        }
        let mut target = TargetCommand::new("/proc/self/exe")
            .argument(PRIVATE_ROLE_ARGUMENT)
            .argument("--domain")
            .argument(hex(ownership.domain_id.as_bytes()))
            .argument("--generation")
            .argument(ownership.generation_id.get().to_string())
            .argument("--coordinator")
            .argument(hex(ownership.coordinator_id.as_bytes()))
            .argument("--runsc")
            .argument(command.program());
        for argument in command.arguments() {
            target = target.argument(argument);
        }
        Ok(Self {
            target: target.with_lifetime_pipe_parent_edge(),
            ownership,
            policy_file: None,
            policy_digest: None,
            configuration_fingerprint: None,
            network_sidecar_id: None,
            runsc_command: command.clone(),
            state_anchor: None,
        })
    }

    /// Builds the RS-owned network path with one inherited sealed policy document.
    ///
    /// # Errors
    /// Refuses an invalid runsc form or a policy descriptor that cannot be sealed and inherited.
    pub fn from_networked_runsc_command(
        ownership: ProcessOwnershipContext,
        command: &RunscCommand,
        network: RuntimeNetworkLaunch<'_>,
    ) -> io::Result<Self> {
        let runtime_supervisor_executable = std::env::current_exe()?;
        let mut launch = Self::from_runsc_command(ownership, command)?;
        let policy_file = sealed_memfd("lazaret-network-policy", network.policy.canonical_bytes())?;
        fcntl_setfd(policy_file.as_fd(), FdFlags::empty())?;
        let policy_fd = policy_file.as_raw_fd();
        let target = std::mem::replace(
            &mut launch.target,
            TargetCommand::new("/usr/bin/false").with_lifetime_pipe_parent_edge(),
        );
        launch.target = TargetCommand::new(runtime_supervisor_executable)
            .argument(PRIVATE_ROLE_ARGUMENT)
            .argument("--domain")
            .argument(hex(ownership.domain_id.as_bytes()))
            .argument("--generation")
            .argument(ownership.generation_id.get().to_string())
            .argument("--coordinator")
            .argument(hex(ownership.coordinator_id.as_bytes()))
            .argument("--network-policy-fd")
            .argument(policy_fd.to_string())
            .argument("--network-policy-digest")
            .argument(hex(network.policy.digest().as_bytes()))
            .argument("--configuration-fingerprint")
            .argument(hex(network.configuration_fingerprint.as_bytes()))
            .argument("--network-sidecar")
            .argument(hex(network.network_sidecar_id.as_bytes()))
            .argument("--runsc")
            .argument(command.program());
        for argument in command.arguments() {
            launch.target = launch.target.argument(argument);
        }
        launch.target = launch.target.with_lifetime_pipe_parent_edge();
        drop(target);
        launch.policy_file = Some(policy_file);
        launch.policy_digest = Some(network.policy.digest());
        launch.configuration_fingerprint = Some(network.configuration_fingerprint);
        launch.network_sidecar_id = Some(network.network_sidecar_id);
        Ok(launch)
    }

    /// Adds exact inherited State Anchor authorities without beginning physical acquisition.
    #[must_use]
    pub fn with_state_anchor(mut self, authority: StateAnchorLaunchAuthority) -> Self {
        self.state_anchor = Some(authority);
        self.rebuild_target();
        self
    }

    fn rebuild_target(&mut self) {
        let mut target = TargetCommand::new("/proc/self/exe")
            .argument(PRIVATE_ROLE_ARGUMENT)
            .argument("--domain")
            .argument(hex(self.ownership.domain_id.as_bytes()))
            .argument("--generation")
            .argument(self.ownership.generation_id.get().to_string())
            .argument("--coordinator")
            .argument(hex(self.ownership.coordinator_id.as_bytes()));
        if let Some(authority) = &self.state_anchor {
            let (device, inode) = authority.expected_lower();
            target = target
                .argument("--state-lower-fd")
                .argument(authority.lower_fd().to_string())
                .argument("--state-lower-label")
                .argument(authority.lower_label())
                .argument("--state-persistent-root-fd")
                .argument(authority.persistent_root_fd().to_string())
                .argument("--state-persistent-fd")
                .argument(authority.persistent_anchor_fd().to_string())
                .argument("--state-persistent-label")
                .argument(authority.persistent_anchor_label())
                .argument("--state-runtime-root-fd")
                .argument(authority.runtime_root_fd().to_string())
                .argument("--state-runtime-fd")
                .argument(authority.runtime_anchor_fd().to_string())
                .argument("--state-runtime-label")
                .argument(authority.runtime_anchor_label())
                .argument("--state-lower-device")
                .argument(device.to_string())
                .argument("--state-lower-inode")
                .argument(inode.to_string())
                .argument("--state-persistent-count")
                .argument(authority.persistent_destinations().len().to_string());
            for destination in authority.persistent_destinations() {
                target = target
                    .argument("--state-persistent-destination")
                    .argument(destination);
            }
        }
        if let (Some(policy_file), Some(digest), Some(fingerprint), Some(sidecar)) = (
            &self.policy_file,
            self.policy_digest,
            self.configuration_fingerprint,
            self.network_sidecar_id,
        ) {
            target = target
                .argument("--network-policy-fd")
                .argument(policy_file.as_raw_fd().to_string())
                .argument("--network-policy-digest")
                .argument(hex(digest.as_bytes()))
                .argument("--configuration-fingerprint")
                .argument(hex(fingerprint.as_bytes()))
                .argument("--network-sidecar")
                .argument(hex(sidecar.as_bytes()));
        }
        target = target
            .argument("--runsc")
            .argument(self.runsc_command.program());
        for argument in self.runsc_command.arguments() {
            target = target.argument(argument);
        }
        self.target = target.with_lifetime_pipe_parent_edge();
    }

    #[must_use]
    pub const fn target(&self) -> &TargetCommand {
        &self.target
    }

    #[must_use]
    pub const fn ownership(&self) -> ProcessOwnershipContext {
        self.ownership
    }

    #[must_use]
    pub const fn network_sidecar_id(&self) -> Option<NetworkSidecarId> {
        self.network_sidecar_id
    }

    #[must_use]
    pub const fn runsc_command(&self) -> &RunscCommand {
        &self.runsc_command
    }

    /// # Errors
    /// Refuses a Runtime Supervisor target without the lifetime-pipe parent edge.
    pub fn child_standard_io(
        &self,
        private_control: OwnedFd,
        lifetime_pipe: OwnedFd,
    ) -> io::Result<ChildStandardIo> {
        if self.target.parent_edge() != ParentEdge::LifetimePipe {
            return Err(io::Error::other(
                "Runtime Supervisor launch requires the lifetime-pipe parent edge",
            ));
        }
        Ok(ChildStandardIo::private_control_with_lifetime_pipe(
            private_control,
            lifetime_pipe,
        ))
    }
}

/// Runs the Runtime Supervisor's private early role before ordinary binary dispatch.
///
/// # Errors
/// Returns a fail-closed parse, acquisition, capability, channel, or process error.
#[must_use]
pub fn dispatch_private_runtime_role(arguments: &[OsString]) -> Option<io::Result<()>> {
    if arguments
        .first()
        .is_none_or(|argument| argument != PRIVATE_ROLE_ARGUMENT)
    {
        return None;
    }
    let result =
        parse_runtime_arguments(&arguments[1..]).and_then(|parsed| run_supervisor(&parsed));
    if let Err(error) = &result {
        let _ = send_message(
            std::io::stdout(),
            &SupervisorEvent::Refused(error.to_string()),
        );
    }
    Some(result)
}

struct RuntimeArguments {
    ownership: ProcessOwnershipContext,
    state_anchor: Option<RuntimeStateAnchorArguments>,
    network: Option<RuntimeNetworkArguments>,
    runsc_program: OsString,
    runsc_arguments: Vec<OsString>,
}

struct RuntimeStateAnchorArguments {
    lower_fd: i32,
    lower_label: PathBuf,
    persistent_root_fd: i32,
    persistent_anchor_fd: i32,
    persistent_anchor_label: PathBuf,
    runtime_root_fd: i32,
    runtime_anchor_fd: i32,
    runtime_anchor_label: PathBuf,
    expected_lower: (u64, u64),
    persistent_destinations: Vec<PathBuf>,
}

struct RuntimeNetworkArguments {
    policy_fd: i32,
    policy_digest: DerivedPolicyDigest,
    configuration_fingerprint: ConfigurationFingerprint,
    network_sidecar_id: NetworkSidecarId,
}

fn parse_runtime_arguments(arguments: &[OsString]) -> io::Result<RuntimeArguments> {
    let mut arguments = arguments.iter().peekable();
    let domain = parse_fixed_hex(named(&mut arguments, "--domain")?)?;
    let generation = named(&mut arguments, "--generation")?
        .to_str()
        .and_then(|value| value.parse().ok())
        .ok_or_else(|| io::Error::other("Runtime Supervisor generation is invalid"))?;
    let coordinator = parse_fixed_hex(named(&mut arguments, "--coordinator")?)?;
    let state_anchor = if arguments
        .peek()
        .is_some_and(|value| *value == "--state-lower-fd")
    {
        let lower_fd = parse_number(named(&mut arguments, "--state-lower-fd")?)?;
        let lower_label = PathBuf::from(named(&mut arguments, "--state-lower-label")?);
        let persistent_root_fd =
            parse_number(named(&mut arguments, "--state-persistent-root-fd")?)?;
        let persistent_anchor_fd = parse_number(named(&mut arguments, "--state-persistent-fd")?)?;
        let persistent_anchor_label =
            PathBuf::from(named(&mut arguments, "--state-persistent-label")?);
        let runtime_root_fd = parse_number(named(&mut arguments, "--state-runtime-root-fd")?)?;
        let runtime_anchor_fd = parse_number(named(&mut arguments, "--state-runtime-fd")?)?;
        let runtime_anchor_label = PathBuf::from(named(&mut arguments, "--state-runtime-label")?);
        let expected_lower = (
            parse_number(named(&mut arguments, "--state-lower-device")?)?,
            parse_number(named(&mut arguments, "--state-lower-inode")?)?,
        );
        let count: usize = parse_number(named(&mut arguments, "--state-persistent-count")?)?;
        let persistent_destinations = (0..count)
            .map(|_| named(&mut arguments, "--state-persistent-destination").map(PathBuf::from))
            .collect::<io::Result<Vec<_>>>()?;
        Some(RuntimeStateAnchorArguments {
            lower_fd,
            lower_label,
            persistent_root_fd,
            persistent_anchor_fd,
            persistent_anchor_label,
            runtime_root_fd,
            runtime_anchor_fd,
            runtime_anchor_label,
            expected_lower,
            persistent_destinations,
        })
    } else {
        None
    };
    let network = if arguments
        .peek()
        .is_some_and(|value| *value == "--network-policy-fd")
    {
        Some(parse_network_arguments(&mut arguments)?)
    } else {
        None
    };
    if arguments.next().is_none_or(|value| value != "--runsc") {
        return Err(io::Error::other(
            "Runtime Supervisor runsc separator is missing",
        ));
    }
    let program = arguments
        .next()
        .ok_or_else(|| io::Error::other("Runtime Supervisor runsc program is missing"))?;
    if program != "runsc" {
        return Err(io::Error::other("Runtime Supervisor target is not runsc"));
    }
    Ok(RuntimeArguments {
        ownership: ProcessOwnershipContext {
            domain_id: DomainId::new(domain),
            generation_id: GenerationId::new(generation),
            coordinator_id: CoordinatorId::new(coordinator),
            slot: HostProcessOwnershipSlot::SandboxAttachedRunsc,
        },
        state_anchor,
        network,
        runsc_program: (*program).clone(),
        runsc_arguments: arguments.cloned().collect(),
    })
}

fn parse_number<T>(value: &OsStr) -> io::Result<T>
where
    T: std::str::FromStr,
{
    value
        .to_str()
        .and_then(|value| value.parse().ok())
        .ok_or_else(|| io::Error::other("Runtime Supervisor numeric argument is invalid"))
}

fn parse_network_arguments<'a>(
    arguments: &mut impl Iterator<Item = &'a OsString>,
) -> io::Result<RuntimeNetworkArguments> {
    let policy_fd = named(arguments, "--network-policy-fd")?
        .to_str()
        .and_then(|value| value.parse().ok())
        .filter(|value| *value >= 0)
        .ok_or_else(|| io::Error::other("Runtime Supervisor policy descriptor is invalid"))?;
    let policy_digest = DerivedPolicyDigest::new(parse_fixed_hex(named(
        arguments,
        "--network-policy-digest",
    )?)?);
    let configuration_fingerprint = ConfigurationFingerprint::new(parse_fixed_hex(named(
        arguments,
        "--configuration-fingerprint",
    )?)?);
    let network_sidecar_id =
        NetworkSidecarId::new(parse_fixed_hex(named(arguments, "--network-sidecar")?)?);
    Ok(RuntimeNetworkArguments {
        policy_fd,
        policy_digest,
        configuration_fingerprint,
        network_sidecar_id,
    })
}

fn named<'a>(
    arguments: &mut impl Iterator<Item = &'a OsString>,
    name: &str,
) -> io::Result<&'a OsString> {
    if arguments.next().is_none_or(|value| value != name) {
        return Err(io::Error::other(format!(
            "Runtime Supervisor argument {name} is missing"
        )));
    }
    arguments
        .next()
        .ok_or_else(|| io::Error::other(format!("Runtime Supervisor argument {name} has no value")))
}

fn parse_fixed_hex(value: &OsStr) -> io::Result<[u8; 32]> {
    let value = value
        .to_str()
        .ok_or_else(|| io::Error::other("Runtime Supervisor identity is not UTF-8"))?;
    if value.len() != 64 || !value.bytes().all(|byte| byte.is_ascii_hexdigit()) {
        return Err(io::Error::other("Runtime Supervisor identity is invalid"));
    }
    let mut bytes = [0_u8; 32];
    for (index, byte) in bytes.iter_mut().enumerate() {
        *byte = u8::from_str_radix(&value[index * 2..index * 2 + 2], 16)
            .map_err(|_| io::Error::other("Runtime Supervisor identity is invalid"))?;
    }
    Ok(bytes)
}

fn run_supervisor(arguments: &RuntimeArguments) -> io::Result<()> {
    require_lifetime_held()?;
    let namespaces = enter_generation_filesystem_namespaces()?;
    if arguments.network.is_none() {
        enter_generation_network_namespace()?;
    }
    let control = std::io::stdout();
    let parent = current_process_identity()?;
    let mut state_anchor = prepare_state_anchor(arguments, parent, namespaces, &control)?;
    let mut state_anchor_absence = None;
    let result = run_supervisor_with_state(
        arguments,
        parent,
        &control,
        namespaces,
        &mut state_anchor,
        &mut state_anchor_absence,
    );
    let cleanup = state_anchor
        .take()
        .map(RuntimeStateAnchorMount::unmount)
        .map(|result| result.map(drop));
    match (result, cleanup) {
        (Err(error), Some(Err(cleanup))) => Err(io::Error::new(
            error.kind(),
            format!("{error}; exact State Anchor cleanup failed: {cleanup}"),
        )),
        (Err(error), _) => Err(error),
        (Ok(()), Some(Err(error))) => Err(io::Error::other(error)),
        (Ok(()), _) => Ok(()),
    }
}

fn prepare_state_anchor(
    arguments: &RuntimeArguments,
    parent: lazaret_core::identity::PidfsProcessIdentityV1,
    namespaces: (
        lazaret_core::identity::NamespaceIdentity,
        lazaret_core::identity::NamespaceIdentity,
    ),
    control: &std::io::Stdout,
) -> io::Result<Option<RuntimeStateAnchorMount>> {
    let Some(state) = &arguments.state_anchor else {
        return Ok(None);
    };
    let command: CoordinatorMessage = receive_message(control)?;
    if command != CoordinatorMessage::MountStateAnchor {
        return Err(io::Error::other(
            "Runtime Supervisor received no State Anchor mount command",
        ));
    }
    let authority = RuntimeStateAnchorAuthority::from_inherited(RuntimeStateAnchorInherited {
        lower_fd: state.lower_fd,
        lower_label: &state.lower_label,
        persistent_root_fd: state.persistent_root_fd,
        persistent_anchor_fd: state.persistent_anchor_fd,
        persistent_anchor_label: &state.persistent_anchor_label,
        runtime_root_fd: state.runtime_root_fd,
        runtime_anchor_fd: state.runtime_anchor_fd,
        runtime_anchor_label: &state.runtime_anchor_label,
        expected_lower: state.expected_lower,
    })
    .map_err(io::Error::other)?;
    let ownership = ProcessOwnershipContext {
        slot: HostProcessOwnershipSlot::StateAnchorDaemon,
        ..arguments.ownership
    };
    let mount = authority
        .acquire(
            parent,
            ownership,
            |staged| send_message(control, &SupervisorEvent::StateAnchorStaged(staged)),
            |staged| match receive_message(control)? {
                CoordinatorMessage::StateAnchorStagedAck(acknowledgment)
                    if acknowledgment.acknowledges(&staged) =>
                {
                    Ok(acknowledgment)
                }
                _ => Err(io::Error::other(
                    "Runtime Supervisor received a mismatched State Anchor acknowledgment",
                )),
            },
            |readiness| {
                send_message(
                    control,
                    &SupervisorEvent::StateAnchorReady {
                        staged: readiness.staged(),
                        user_namespace: namespaces.0,
                        mount_namespace: namespaces.1,
                        mount: readiness.mount(),
                    },
                )
            },
        )
        .map_err(io::Error::other)?;
    mount
        .require_persistent_destinations(&state.persistent_destinations)
        .map_err(io::Error::other)?;
    Ok(Some(mount))
}

fn run_supervisor_with_state(
    arguments: &RuntimeArguments,
    parent: lazaret_core::identity::PidfsProcessIdentityV1,
    control: &std::io::Stdout,
    namespaces: (NamespaceIdentity, NamespaceIdentity),
    state_anchor: &mut Option<RuntimeStateAnchorMount>,
    state_anchor_absence: &mut Option<RuntimeStateAnchorAbsenceAuthority>,
) -> io::Result<()> {
    if arguments.state_anchor.is_some() {
        let message: CoordinatorMessage = receive_message(control)?;
        if message != CoordinatorMessage::StartSidecar {
            return Err(io::Error::other(
                "Runtime Supervisor received no sidecar start command",
            ));
        }
        send_message(control, &SupervisorEvent::SidecarStarted)?;
    }
    let network = match &arguments.network {
        Some(network) => Some(prepare_runtime_network(
            arguments, network, parent, control,
        )?),
        None => None,
    };
    let pid_file = File::from(memfd_create("lazaret-runsc-pid", MemfdFlags::empty())?);
    fcntl_setfd(pid_file.as_fd(), FdFlags::empty())?;
    let runsc = runsc_target(arguments, pid_file.as_raw_fd())?;
    let delete = runsc_delete_target(arguments)?;
    let staged = std::cell::Cell::new(None);
    let process = match child_broker().acquire_with_stdio(
        parent,
        arguments.ownership,
        &runsc,
        attached_runsc_standard_io(&runsc)?,
        |ownership| {
            staged.set(Some(ownership));
            send_message(control, &SupervisorEvent::Staged(ownership))
        },
        |ownership| match receive_message(control)? {
            CoordinatorMessage::StagedAck(acknowledgment)
                if acknowledgment.acknowledges(&ownership) =>
            {
                Ok(acknowledgment)
            }
            _ => Err(io::Error::other(
                "Runtime Supervisor received a mismatched staged acknowledgment",
            )),
        },
    ) {
        Ok(process) => process,
        Err(error) => return fail_network(network, error),
    };
    if let Err(error) = fcntl_setfd(pid_file.as_fd(), FdFlags::CLOEXEC) {
        return fail_with_network_cleanup(process, network, error.into());
    }
    let Some(staged) = staged.get() else {
        return fail_with_network_cleanup(
            process,
            network,
            io::Error::other("attached runsc ownership was not staged"),
        );
    };
    let sentry_pid_inventory = match wait_for_runsc_ready(&pid_file, &process) {
        Ok(pid) => pid,
        Err(error) => return fail_with_network_cleanup(process, network, error),
    };
    if let Err(error) = capability::irreversibly_drop(CapabilitySet::NET_ADMIN) {
        return fail_with_network_cleanup(process, network, error);
    }
    if let Err(error) = capability::require_regain_refused(CapabilitySet::NET_ADMIN) {
        return fail_with_network_cleanup(process, network, error);
    }
    if let Err(error) = send_message(
        control,
        &SupervisorEvent::Ready {
            staged,
            sentry_pid_inventory,
        },
    ) {
        return fail_with_network_cleanup(process, network, error);
    }
    let committed: CoordinatorMessage = match receive_message(control) {
        Ok(committed) => committed,
        Err(error) => return fail_with_network_cleanup(process, network, error),
    };
    if committed != CoordinatorMessage::SandboxCommitted {
        return fail_with_network_cleanup(
            process,
            network,
            io::Error::other("sandbox commit acknowledgment was not received"),
        );
    }
    supervise(
        control,
        process,
        network,
        namespaces,
        state_anchor,
        state_anchor_absence,
        &delete,
    )
}

fn prepare_runtime_network(
    arguments: &RuntimeArguments,
    network: &RuntimeNetworkArguments,
    runtime_supervisor: lazaret_core::identity::PidfsProcessIdentityV1,
    control: &std::io::Stdout,
) -> io::Result<PreparedNetwork> {
    let policy_file = File::open(format!("/proc/self/fd/{}", network.policy_fd))?;
    let staged = std::cell::Cell::new(None);
    let prepared = prepare_network(
        &policy_file,
        network.policy_digest,
        NetworkAttestationContext {
            domain_id: arguments.ownership.domain_id,
            generation_id: arguments.ownership.generation_id,
            configuration_fingerprint: network.configuration_fingerprint,
            network_sidecar_id: network.network_sidecar_id,
            runtime_supervisor,
            coordinator_id: arguments.ownership.coordinator_id,
        },
        |ownership| {
            staged.set(Some(ownership));
            send_message(control, &SupervisorEvent::HelperStaged(ownership))
        },
        |ownership| match receive_message(control)? {
            CoordinatorMessage::HelperStagedAck(acknowledgment)
                if acknowledgment.acknowledges(&ownership) =>
            {
                Ok(acknowledgment)
            }
            _ => Err(io::Error::other(
                "Runtime Supervisor received a mismatched helper acknowledgment",
            )),
        },
    )?;
    let staged = staged
        .get()
        .ok_or_else(|| io::Error::other("connectivity helper ownership was not staged"))?;
    if let Err(error) = send_message(control, &SupervisorEvent::HelperReady(staged)) {
        return fail_network(Some(prepared), error);
    }
    if let Err(error) = send_message(
        control,
        &SupervisorEvent::NetworkAttestation(prepared.attestation().clone()),
    ) {
        return fail_network(Some(prepared), error);
    }
    let message: CoordinatorMessage = match receive_message(control) {
        Ok(message) => message,
        Err(error) => return fail_network(Some(prepared), error),
    };
    let CoordinatorMessage::NetworkAttestationAccepted(request) = message else {
        return fail_network(
            Some(prepared),
            io::Error::other("network attestation acceptance was not received"),
        );
    };
    let probe = match probe_current_network(&request) {
        Ok(probe) => probe,
        Err(error) => return fail_network(Some(prepared), error),
    };
    if let Err(error) = send_message(control, &SupervisorEvent::NetworkProbe(probe)) {
        return fail_network(Some(prepared), error);
    }
    let committed: CoordinatorMessage = match receive_message(control) {
        Ok(message) => message,
        Err(error) => return fail_network(Some(prepared), error),
    };
    if committed != CoordinatorMessage::NetworkReadinessCommitted {
        return fail_network(
            Some(prepared),
            io::Error::other("durable network readiness was not acknowledged"),
        );
    }
    Ok(prepared)
}

fn runsc_target(arguments: &RuntimeArguments, pid_file: i32) -> io::Result<TargetCommand> {
    let run = arguments
        .runsc_arguments
        .iter()
        .position(|argument| argument == "run")
        .ok_or_else(|| io::Error::other("attached runsc command has no run operation"))?;
    let mut target = TargetCommand::new(arguments.runsc_program.clone());
    for argument in &arguments.runsc_arguments[..=run] {
        target = target.argument(argument);
    }
    target = target.argument(format!("-pid-file=/proc/self/fd/{pid_file}"));
    for argument in &arguments.runsc_arguments[run + 1..] {
        target = target.argument(argument);
    }
    Ok(target.with_parent_death_kill_edge())
}

fn runsc_delete_target(arguments: &RuntimeArguments) -> io::Result<TargetCommand> {
    let run = arguments
        .runsc_arguments
        .iter()
        .position(|argument| argument == "run")
        .ok_or_else(|| io::Error::other("attached runsc command has no run operation"))?;
    let container = arguments
        .runsc_arguments
        .last()
        .filter(|container| {
            !container.is_empty() && !container.as_encoded_bytes().starts_with(b"-")
        })
        .ok_or_else(|| io::Error::other("attached runsc command has no container ID"))?;
    let mut target = TargetCommand::new(arguments.runsc_program.clone());
    for argument in &arguments.runsc_arguments[..run] {
        target = target.argument(argument);
    }
    Ok(target
        .argument("delete")
        .argument("--force")
        .argument(container))
}

fn attached_runsc_standard_io(target: &TargetCommand) -> io::Result<ChildStandardIo> {
    if target.parent_edge() != ParentEdge::ParentDeathKill {
        return Err(io::Error::other(
            "attached runsc requires the parent-death KILL edge",
        ));
    }
    Ok(ChildStandardIo::silenced())
}

fn wait_for_runsc_ready(pid_file: &File, process: &RetainedProcess) -> io::Result<u32> {
    let deadline = Instant::now() + READINESS_TIMEOUT;
    let mut bytes = [0_u8; 32];
    loop {
        require_lifetime_held()?;
        if process.has_exited()? {
            return Err(io::Error::other("attached runsc exited before readiness"));
        }
        let length = pid_file.read_at(&mut bytes, 0)?;
        if length > 0 {
            return std::str::from_utf8(&bytes[..length])
                .ok()
                .map(str::trim)
                .and_then(|value| value.parse().ok())
                .filter(|pid| *pid > 0)
                .ok_or_else(|| io::Error::other("runsc pid-file readiness is malformed"));
        }
        if Instant::now() >= deadline {
            return Err(io::Error::other("attached runsc readiness timed out"));
        }
        std::thread::sleep(Duration::from_millis(5));
    }
}

fn supervise(
    control: &std::io::Stdout,
    process: RetainedProcess,
    mut network: Option<PreparedNetwork>,
    namespaces: (NamespaceIdentity, NamespaceIdentity),
    state_anchor: &mut Option<RuntimeStateAnchorMount>,
    state_anchor_absence: &mut Option<RuntimeStateAnchorAbsenceAuthority>,
    delete: &TargetCommand,
) -> io::Result<()> {
    let mut process = Some(process);
    let mut state_anchor = StateAnchorSupervision {
        namespaces,
        mount: state_anchor,
        absence: state_anchor_absence,
    };
    loop {
        let exited = match process
            .as_ref()
            .map_or(Ok(false), RetainedProcess::has_exited)
        {
            Ok(exited) => exited,
            Err(error) => return fail_active_runtime(process, network, error),
        };
        if exited {
            child_broker().reap(
                process
                    .take()
                    .ok_or_else(|| io::Error::other("attached runsc handle is absent"))?,
            )?;
            child_broker().run_transient(delete)?;
            stop_network(network)?;
            send_message(control, &SupervisorEvent::AttachedRunscExited)?;
            return Ok(());
        }
        if network
            .as_ref()
            .is_some_and(|network| network.helper_exited().unwrap_or(true))
        {
            network
                .take()
                .ok_or_else(|| io::Error::other("connectivity helper handle is absent"))?
                .reap_exited()?;
            send_message(control, &SupervisorEvent::HelperExited)?;
        }
        let lease_lost = match lifetime_lost() {
            Ok(lost) => lost,
            Err(error) => return fail_active_runtime(process, network, error),
        };
        if lease_lost {
            if let Some(process) = process.take() {
                terminate_and_reap(process)?;
                child_broker().run_transient(delete)?;
            }
            stop_network(network)?;
            return Ok(());
        }
        let mut descriptors = [PollFd::new(control, PollFlags::IN)];
        if let Err(error) = poll(
            &mut descriptors,
            Some(&Timespec {
                tv_sec: 0,
                tv_nsec: 10_000_000,
            }),
        ) {
            return fail_active_runtime(process, network, error.into());
        }
        let events = descriptors[0].revents();
        if events.intersects(PollFlags::HUP | PollFlags::ERR) {
            return fail_active_runtime(
                process,
                network,
                io::Error::new(
                    io::ErrorKind::UnexpectedEof,
                    "runtime control channel closed",
                ),
            );
        }
        if events.intersects(PollFlags::IN) {
            let message = match receive_message(control) {
                Ok(message) => message,
                Err(error) => return fail_active_runtime(process, network, error),
            };
            match handle_supervisor_message(
                control,
                &message,
                &mut process,
                &mut network,
                &mut state_anchor,
                delete,
            ) {
                Ok(true) => return Ok(()),
                Ok(false) => {}
                Err(error) => return fail_active_runtime(process, network, error),
            }
        }
    }
}

struct StateAnchorSupervision<'a> {
    namespaces: (NamespaceIdentity, NamespaceIdentity),
    mount: &'a mut Option<RuntimeStateAnchorMount>,
    absence: &'a mut Option<RuntimeStateAnchorAbsenceAuthority>,
}

fn handle_supervisor_message(
    control: &std::io::Stdout,
    message: &CoordinatorMessage,
    process: &mut Option<RetainedProcess>,
    network: &mut Option<PreparedNetwork>,
    state_anchor: &mut StateAnchorSupervision<'_>,
    delete: &TargetCommand,
) -> io::Result<bool> {
    match message {
        CoordinatorMessage::SignalAttachedRunsc(signal) => {
            process
                .as_ref()
                .ok_or_else(|| io::Error::other("attached runsc is already stopped"))?
                .send_signal(signal.signal())?;
            send_message(control, &SupervisorEvent::SignalApplied(*signal))?;
        }
        CoordinatorMessage::StopSandbox => {
            terminate_and_reap(
                process
                    .take()
                    .ok_or_else(|| io::Error::other("attached runsc is already stopped"))?,
            )?;
            child_broker().run_transient(delete)?;
            send_message(control, &SupervisorEvent::SandboxStopped)?;
        }
        CoordinatorMessage::StopSidecar => {
            if process.is_some() {
                return Err(io::Error::other("sidecar stop preceded sandbox stop"));
            }
            stop_network(network.take())?;
            send_message(control, &SupervisorEvent::SidecarStopped)?;
        }
        CoordinatorMessage::UnmountStateAnchor
        | CoordinatorMessage::ObserveStateAnchorAbsence { .. } => {
            handle_state_anchor_message(
                control,
                message,
                process.is_some() || network.is_some(),
                state_anchor,
            )?;
        }
        CoordinatorMessage::Exit => {
            if process.is_some() || network.is_some() || state_anchor.mount.is_some() {
                return Err(io::Error::other(
                    "Runtime Supervisor exit preceded resource cleanup",
                ));
            }
            send_message(control, &SupervisorEvent::Exited)?;
            return Ok(true);
        }
        CoordinatorMessage::Stop => {
            if let Some(process) = process.take() {
                terminate_and_reap(process)?;
            }
            stop_network(network.take())?;
            send_message(control, &SupervisorEvent::Stopped)?;
            return Ok(true);
        }
        CoordinatorMessage::HelperStagedAck(_)
        | CoordinatorMessage::MountStateAnchor
        | CoordinatorMessage::StateAnchorStagedAck(_)
        | CoordinatorMessage::StartSidecar
        | CoordinatorMessage::NetworkAttestationAccepted(_)
        | CoordinatorMessage::NetworkReadinessCommitted
        | CoordinatorMessage::StagedAck(_)
        | CoordinatorMessage::SandboxCommitted => {
            return Err(io::Error::other("unexpected duplicate coordinator message"));
        }
    }
    Ok(false)
}

fn handle_state_anchor_message(
    control: &std::io::Stdout,
    message: &CoordinatorMessage,
    runtime_resources_present: bool,
    state: &mut StateAnchorSupervision<'_>,
) -> io::Result<()> {
    match message {
        CoordinatorMessage::UnmountStateAnchor => {
            if runtime_resources_present {
                return Err(io::Error::other(
                    "State Anchor unmount preceded runtime resource stop",
                ));
            }
            let mount = state
                .mount
                .as_ref()
                .ok_or_else(|| io::Error::other("State Anchor is absent"))?
                .mount_identity();
            let absence = state
                .mount
                .take()
                .ok_or_else(|| io::Error::other("State Anchor is absent"))?
                .unmount()
                .map_err(io::Error::other)?;
            *state.absence = Some(absence);
            send_message(control, &SupervisorEvent::StateAnchorUnmounted { mount })
        }
        CoordinatorMessage::ObserveStateAnchorAbsence {
            user_namespace,
            mount_namespace,
            mount,
        } => {
            if (*user_namespace, *mount_namespace) != state.namespaces {
                return send_message(
                    control,
                    &SupervisorEvent::Refused(
                        "State Anchor absence request namespace authority mismatched".into(),
                    ),
                );
            }
            match state.absence.as_ref().map_or_else(
                || {
                    Err(lazaret_state_anchor::StateAnchorError::InvalidLayout(
                        "State Anchor absence authority is absent",
                    ))
                },
                |authority| authority.observe_absence(*mount),
            ) {
                Ok(observed) => send_message(
                    control,
                    &SupervisorEvent::StateAnchorAbsenceObserved {
                        user_namespace: state.namespaces.0,
                        mount_namespace: state.namespaces.1,
                        mount: *mount,
                        observed,
                    },
                ),
                Err(error) => send_message(control, &SupervisorEvent::Refused(error.to_string())),
            }
        }
        _ => Err(io::Error::other("message is not a State Anchor command")),
    }
}

fn fail_active_runtime(
    process: Option<RetainedProcess>,
    network: Option<PreparedNetwork>,
    error: io::Error,
) -> io::Result<()> {
    if let Some(process) = process {
        fail_with_network_cleanup(process, network, error)
    } else {
        let _ = stop_network(network);
        Err(error)
    }
}

fn terminate_and_reap(process: RetainedProcess) -> io::Result<()> {
    let term_error = process.send_signal(Signal::TERM).err();
    let deadline = Instant::now() + TERMINATION_GRACE;
    while !process.has_exited()? && Instant::now() < deadline {
        std::thread::sleep(Duration::from_millis(5));
    }
    if !process.has_exited()? {
        process.send_signal(Signal::KILL)?;
    }
    child_broker().reap(process)?;
    if let Some(error) = term_error {
        Err(error)
    } else {
        Ok(())
    }
}

fn fail_with_network_cleanup(
    process: RetainedProcess,
    network: Option<PreparedNetwork>,
    error: io::Error,
) -> io::Result<()> {
    let runsc_cleanup = terminate_and_reap(process);
    let network_cleanup = stop_network(network);
    match (runsc_cleanup, network_cleanup) {
        (Ok(()), Ok(())) => Err(error),
        (runsc, network) => Err(io::Error::new(
            error.kind(),
            format!("{error}; exact runtime cleanup failed: runsc={runsc:?}, network={network:?}"),
        )),
    }
}

fn fail_network<T>(network: Option<PreparedNetwork>, error: io::Error) -> io::Result<T> {
    match stop_network(network) {
        Ok(()) => Err(error),
        Err(cleanup) => Err(io::Error::new(
            error.kind(),
            format!("{error}; exact connectivity-helper cleanup failed: {cleanup}"),
        )),
    }
}

fn stop_network(network: Option<PreparedNetwork>) -> io::Result<()> {
    match network {
        Some(network) => network.stop(),
        None => Ok(()),
    }
}

fn require_lifetime_held() -> io::Result<()> {
    if lifetime_lost()? {
        Err(io::Error::other("Host Coordinator lifetime lease is lost"))
    } else {
        Ok(())
    }
}

fn lifetime_lost() -> io::Result<bool> {
    let stderr = std::io::stderr();
    let mut descriptors = [PollFd::new(&stderr, PollFlags::IN)];
    poll(&mut descriptors, Some(&Timespec::default()))?;
    Ok(descriptors[0]
        .revents()
        .intersects(PollFlags::IN | PollFlags::HUP | PollFlags::ERR))
}

fn send_message<T: Serialize>(descriptor: impl AsFd, message: &T) -> io::Result<()> {
    let encoded = encode(message).map_err(|error| io::Error::other(error.to_string()))?;
    if encoded.len() > MAX_CONTROL_MESSAGE {
        return Err(io::Error::other("runtime control message is oversized"));
    }
    let length = u32::try_from(encoded.len())
        .map_err(|_| io::Error::other("runtime control message is oversized"))?
        .to_be_bytes();
    send_all(descriptor.as_fd(), &length)?;
    send_all(descriptor.as_fd(), &encoded)
}

fn receive_message<T>(descriptor: impl AsFd) -> io::Result<T>
where
    T: serde::de::DeserializeOwned + Serialize,
{
    let mut length = [0_u8; 4];
    receive_exact(descriptor.as_fd(), &mut length)?;
    let length = usize::try_from(u32::from_be_bytes(length))
        .map_err(|_| io::Error::other("runtime control length is invalid"))?;
    if length > MAX_CONTROL_MESSAGE {
        return Err(io::Error::other("runtime control message is oversized"));
    }
    let mut encoded = vec![0_u8; length];
    receive_exact(descriptor.as_fd(), &mut encoded)?;
    decode(&encoded).map_err(|error| io::Error::other(error.to_string()))
}

fn send_all(descriptor: impl AsFd + Copy, mut bytes: &[u8]) -> io::Result<()> {
    while !bytes.is_empty() {
        let sent = write(descriptor, bytes)?;
        if sent == 0 {
            return Err(io::Error::new(
                io::ErrorKind::WriteZero,
                "runtime control channel closed",
            ));
        }
        bytes = &bytes[sent..];
    }
    Ok(())
}

fn receive_exact(descriptor: impl AsFd + Copy, mut bytes: &mut [u8]) -> io::Result<()> {
    while !bytes.is_empty() {
        let received = read(descriptor, &mut *bytes)?;
        if received == 0 {
            return Err(io::Error::new(
                io::ErrorKind::UnexpectedEof,
                "runtime control channel closed",
            ));
        }
        bytes = &mut bytes[received..];
    }
    Ok(())
}

fn hex(bytes: &[u8]) -> String {
    use std::fmt::Write as _;

    bytes.iter().fold(String::new(), |mut output, byte| {
        write!(output, "{byte:02x}").expect("writing to a String cannot fail");
        output
    })
}

#[cfg(test)]
mod tests {
    use std::ffi::OsString;

    use lazaret_core::identity::{CoordinatorId, DomainId, GenerationId};
    use lazaret_core::records::HostProcessOwnershipSlot;
    use lazaret_linux::ipc::private_seqpacket_pair;
    use lazaret_linux::process::ChildStandardIoPolicy;
    use rustix::pipe::{PipeFlags, pipe_with};

    use super::*;

    #[test]
    fn private_stream_framing_round_trips_typed_events() {
        let (coordinator, supervisor) = private_seqpacket_pair().unwrap();
        let expected = SupervisorEvent::Refused("refused".into());
        send_message(&supervisor, &expected).unwrap();
        assert_eq!(
            CoordinatorChannel::new(coordinator).receive().unwrap(),
            expected
        );
    }

    #[test]
    fn coordinator_channel_preserves_phased_resource_commands() {
        let (coordinator, supervisor) = private_seqpacket_pair().unwrap();
        let channel = CoordinatorChannel::new(coordinator);
        channel.mount_state_anchor().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::MountStateAnchor
        );
        channel.start_sidecar().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::StartSidecar
        );
        channel.stop_sandbox().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::StopSandbox
        );
        channel.stop_sidecar().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::StopSidecar
        );
        channel.unmount_state_anchor().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::UnmountStateAnchor
        );
        let user_namespace = NamespaceIdentity {
            device: lazaret_core::identity::DeviceId::new(11),
            inode: lazaret_core::identity::InodeId::new(12),
        };
        let mount_namespace = NamespaceIdentity {
            device: lazaret_core::identity::DeviceId::new(13),
            inode: lazaret_core::identity::InodeId::new(14),
        };
        let mount = MountIdentity {
            mount_id: lazaret_core::identity::MountId::new(15),
            device: lazaret_core::identity::DeviceId::new(16),
            inode: lazaret_core::identity::InodeId::new(17),
        };
        channel
            .observe_state_anchor_absence(user_namespace, mount_namespace, mount)
            .unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::ObserveStateAnchorAbsence {
                user_namespace,
                mount_namespace,
                mount,
            }
        );
        channel.exit().unwrap();
        assert_eq!(
            receive_message::<CoordinatorMessage>(&supervisor).unwrap(),
            CoordinatorMessage::Exit
        );
    }

    #[test]
    fn runtime_supervisor_and_runsc_keep_distinct_edge_and_stdio_policies() {
        let ownership = ProcessOwnershipContext {
            domain_id: DomainId::new([1; 32]),
            generation_id: GenerationId::new(7),
            coordinator_id: CoordinatorId::new([2; 32]),
            slot: HostProcessOwnershipSlot::SandboxRuntimeSupervisor,
        };
        let launch = RuntimeSupervisorLaunch {
            target: TargetCommand::new("/proc/self/exe").with_lifetime_pipe_parent_edge(),
            ownership,
            policy_file: None,
            policy_digest: None,
            configuration_fingerprint: None,
            runsc_command: RunscCommand::new(
                "runsc",
                [OsString::from("run"), OsString::from("container")],
                [0; 32],
            ),
            network_sidecar_id: None,
            state_anchor: None,
        };
        let (_coordinator_control, supervisor_control) = private_seqpacket_pair().unwrap();
        let (supervisor_lifetime, _coordinator_lifetime) = pipe_with(PipeFlags::CLOEXEC).unwrap();
        assert_eq!(launch.target().parent_edge(), ParentEdge::LifetimePipe);
        assert_eq!(
            launch
                .child_standard_io(supervisor_control, supervisor_lifetime)
                .unwrap()
                .policy(),
            ChildStandardIoPolicy::PrivateControlWithLifetimePipe
        );

        let runsc_arguments = RuntimeArguments {
            ownership: ProcessOwnershipContext {
                slot: HostProcessOwnershipSlot::SandboxAttachedRunsc,
                ..ownership
            },
            state_anchor: None,
            network: None,
            runsc_program: "runsc".into(),
            runsc_arguments: ["-root=/runtime", "run", "container"]
                .map(OsString::from)
                .into(),
        };
        let runsc = runsc_target(&runsc_arguments, 9).unwrap();
        assert_eq!(runsc.parent_edge(), ParentEdge::ParentDeathKill);
        assert_eq!(
            attached_runsc_standard_io(&runsc).unwrap().policy(),
            ChildStandardIoPolicy::Silenced
        );
        let delete = runsc_delete_target(&runsc_arguments).unwrap();
        assert_eq!(delete.program(), "runsc");
        assert_eq!(
            delete.arguments(),
            ["-root=/runtime", "delete", "--force", "container"]
                .map(OsString::from)
                .as_slice()
        );
    }

    #[test]
    fn runtime_role_parser_preserves_exact_ownership_and_runsc_arguments() {
        let domain = [1_u8; 32];
        let coordinator = [2_u8; 32];
        let arguments = [
            "--domain".into(),
            hex(&domain).into(),
            "--generation".into(),
            "7".into(),
            "--coordinator".into(),
            hex(&coordinator).into(),
            "--runsc".into(),
            "runsc".into(),
            "-root=/runtime".into(),
            "run".into(),
            "container".into(),
        ];
        let parsed = parse_runtime_arguments(&arguments).unwrap();
        assert_eq!(parsed.ownership.domain_id, DomainId::new(domain));
        assert_eq!(parsed.ownership.generation_id, GenerationId::new(7));
        assert_eq!(
            parsed.ownership.coordinator_id,
            CoordinatorId::new(coordinator)
        );
        assert_eq!(
            parsed.ownership.slot,
            HostProcessOwnershipSlot::SandboxAttachedRunsc
        );
        assert_eq!(parsed.runsc_program, OsString::from("runsc"));
        assert_eq!(
            parsed.runsc_arguments,
            ["-root=/runtime", "run", "container"].map(OsString::from)
        );
    }

    #[test]
    fn runtime_role_parser_refuses_non_runsc_target() {
        let arguments = [
            "--domain".into(),
            hex(&[1_u8; 32]).into(),
            "--generation".into(),
            "7".into(),
            "--coordinator".into(),
            hex(&[2_u8; 32]).into(),
            "--runsc".into(),
            "foreign-runtime".into(),
        ];
        assert!(parse_runtime_arguments(&arguments).is_err());
    }
}