mj_controller/

controller.rs

//! Controller-side lifecycle transitions and canonical-to-backend conversion.

mod backend;
mod cache_host;
pub(crate) mod checkpoint;
mod git_cache;
mod github_app;
mod lifecycle;
pub mod local_profile_homes;
pub(crate) mod mbx;
pub mod move_session;
mod network_git;
mod new_session_preflight;
pub use new_session_preflight::{NewSessionPreflight, NewSessionRepository};
mod path_completion;
pub mod profile_config;
mod provisioning;
pub(crate) mod publication;
mod readiness;
pub(crate) use network_git::workspace_root;
pub(crate) use readiness::HarnessPreparationFailure;
pub(crate) use readiness::NATIVE_SESSION_STARTUP_TIMEOUT;
mod recovery_scan;
mod resume;
mod reviewer;
mod subagent_park;
pub use subagent_park::ParkOutcome;
pub(crate) use subagent_park::{FAILED_STARTUP_CLEANUP_TIMEOUT, failed_launch_cleanup_executor};
mod subagents;
#[cfg(test)]
pub(crate) mod test_support;
pub mod update;
mod worker_binary;
mod worker_restart;
mod worktree;
pub(crate) use worktree::RemoteGitExecutor;

use std::collections::{BTreeMap, BTreeSet};
use std::fs::{self, File, OpenOptions};
use std::path::{Path, PathBuf};

use anyhow::{Context, Result, bail, ensure};
use chrono::Utc;

use mj_core::config::{
    Config, ProjectBundle, ProjectRepository, TargetTemplate, atomic_write, container_size_host,
    data_dir, is_bare_project_target, mount_history_host,
};

use crate::import::{RepositoryIdentity, setup_style_id};
use crate::setup::github_repository_from_origin;

const CONFIG_RENAME_JOURNAL: &str = "config-rename.json";

#[derive(Debug, Clone, Copy, serde::Serialize, serde::Deserialize)]
#[serde(rename_all = "snake_case")]
enum ConfigRenameKind {
    Profile,
    Target,
}

#[derive(Debug, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
struct ConfigRenameJournal {
    kind: ConfigRenameKind,
    old_id: String,
    new_id: String,
}
use mj_core::state::{
    HostContainerSize, SessionRecord, SessionResourceAllocation, SessionState, State,
    new_session_id, normalize_session_title,
};

use crate::targets::{
    self, AdditionalMount, CommandExecutor, CommandOutput, CommandSpec, SshTarget,
};

pub(crate) use backend::backend_locator;
pub(crate) use backend::controller_github_token;
pub use backend::image_refresh_plan;
pub(crate) use backend::validate_resource_allocation;
pub(crate) use backend::{LocalEngineReadiness, local_engine_readiness};
pub use github_app::GithubBundleSelectionError;
pub(crate) use github_app::{
    GithubAppTokenProvider, github_app_token_for_session, github_token_for_session,
};
pub use mbx::install::{
    MbxInstallKind, MbxInstallResult, install_kind as mbx_install_kind, install_mbx,
};
pub use mbx::preview_build_cache;
pub(crate) use mbx::release::{FAILURE_REPORT_SECS, ReleaseFailure, recent_release_failures};
pub(crate) use mbx::{DoctorHostMbxStatus, MBX_VERSION, doctor_host_mbx};
use provisioning::apply_failed_new_session_rollback;
pub(crate) use worker_binary::{
    prepare_recovery_worker_binary, recorded_exit_reason, refresh_target_worker_binary_if_stale,
    worker_source_problem,
};
pub(crate) use worktree::path_exists_on_managed_target;

pub use checkpoint::{
    CheckpointArtifact, CheckpointDeferred, IdleWorkspaceLease, SessionExportLayout,
    checkpoint_was_deferred, reconcile_managed_checkpoint_archives,
    sweep_local_checkpoint_leftovers,
};
pub use lifecycle::{
    BeforeClose, BranchDisposition, CheckoutDisposition, has_nothing_to_checkpoint,
};
pub use recovery_scan::{RecoveryCandidate, RecoveryScan};
pub(crate) use resume::InPlaceRestartError;
pub use resume::{
    ResumeRepositorySourceMismatch, ResumeRepositorySourcePreflight, ResumeRepositorySourceReceipt,
    raw_conversion_preview_for,
};
pub use reviewer::reviewer_stager;
pub use subagents::{RegisterSubagentRequest, stopped_subagent, subagent_has_handed_back};
pub use worker_binary::{
    WorkerBinaryAvailability, native_worker_binary_prerequisite, pin_worker_binary_sources,
    ssh_worker_binary_prerequisite, warm_worker_binary_sources,
    worker_binary_prerequisite_for_arch,
};
pub use worker_restart::WorkerUpgradeOutcome;
pub use worktree::{
    ResumePlan, local_project_repository, resume_compatibility, resume_compatibility_with_checkout,
};

pub struct Controller {
    pub config: Config,
    pub state: State,
}

/// Machine-wide advisory lock for one controller data store. This prevents a
/// dashboard, server, or CLI lifecycle command from concurrently acting as a
/// second controller against the same SQLite state and relay sessions.
#[derive(Debug)]
pub struct ControllerStoreGuard {
    file: File,
}

impl ControllerStoreGuard {
    pub fn acquire() -> Result<Self> {
        let directory = data_dir();
        Self::acquire_at(&directory)
    }

    fn acquire_at(directory: &Path) -> Result<Self> {
        Self::try_acquire_at(directory)?.with_context(|| {
            format!(
                "another Mjolnir controller is already using {}; stop it before starting this command",
                directory.display()
            )
        })
    }

    /// Probe exclusivity without treating an owner that is still exiting as an error.
    pub fn try_acquire() -> Result<Option<Self>> {
        Self::try_acquire_at(&data_dir())
    }

    fn try_acquire_at(directory: &Path) -> Result<Option<Self>> {
        // The lock holder starts the database writer, which migrates the store.
        mj_core::config::ensure_may_control_store(directory, "own this data store")?;
        std::fs::create_dir_all(directory)
            .with_context(|| format!("create controller data directory {}", directory.display()))?;
        let path = directory.join("controller.lock");
        let mut options = OpenOptions::new();
        options.create(true).read(true).write(true);
        #[cfg(unix)]
        {
            use std::os::unix::fs::OpenOptionsExt;
            options.mode(0o600);
        }
        let file = options
            .open(&path)
            .with_context(|| format!("open controller lock {}", path.display()))?;
        match file.try_lock() {
            Ok(()) => {}
            Err(std::fs::TryLockError::WouldBlock) => return Ok(None),
            Err(std::fs::TryLockError::Error(error)) => {
                return Err(error)
                    .with_context(|| format!("lock controller store {}", directory.display()));
            }
        }
        Ok(Some(Self { file }))
    }

    /// Start the sole production SQLite writer after controller exclusivity
    /// has been established by this guard.
    pub fn start_database_writer(&self) -> Result<crate::database::DatabaseWriterOwner> {
        crate::database::start_database_writer()
    }
}

impl Drop for ControllerStoreGuard {
    fn drop(&mut self) {
        // Make release explicit. `File` also unlocks on close, but an explicit
        // unlock keeps same-process handoff deterministic across platforms.
        let _ = self.file.unlock();
    }
}

/// The durable result of creating a quick bundle. The returned config is the
/// same fresh config that was written, allowing a serving projection to publish
/// the new bundle before acknowledging the request that created it.
#[derive(Debug)]
pub struct QuickBundleCreation {
    pub config: Config,
    pub bundle_id: String,
}

/// Failure stages exposed to a viewer request without exposing the underlying
/// filesystem/configuration error. The detailed error remains available to
/// the caller for logs and terminal notices.
#[derive(Debug)]
pub enum QuickBundleFailure {
    InvalidSource(anyhow::Error),
    Persistence(anyhow::Error),
}

impl std::fmt::Display for QuickBundleFailure {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::InvalidSource(error) => write!(formatter, "invalid repository source: {error}"),
            Self::Persistence(error) => write!(formatter, "persist quick bundle: {error}"),
        }
    }
}

impl std::error::Error for QuickBundleFailure {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::InvalidSource(error) | Self::Persistence(error) => Some(error.root_cause()),
        }
    }
}

/// Create a quick bundle from a local repository or GitHub source and persist
/// it as one serialized fresh-config transaction. Identical sources reuse the
/// existing configured bundle, matching the terminal's behavior. The returned
/// config is the same fresh config that was written, allowing a serving
/// projection to publish the new bundle before acknowledging the request.
pub fn create_quick_bundle(
    source: &str,
) -> std::result::Result<QuickBundleCreation, QuickBundleFailure> {
    create_bundle_from_sources(&[source.to_owned()])
}

/// Add a quick bundle to an already-loaded config. The helper still performs
/// the local repository canonicalization/GitHub-source parsing, but callers
/// that persist a config should use [`create_quick_bundle`] so concurrent saves
/// cannot clobber one another.
pub fn create_quick_bundle_in_config(config: &mut Config, source: &str) -> Result<String> {
    create_bundle_from_sources_in_config(config, &[source.to_owned()])
}

/// Create one bundle from one or more local repositories or GitHub sources.
///
/// All sources are interpreted and checked before the config transaction can
/// write anything. An existing bundle is reused only when its repository set
/// and primary repository exactly match the request; this keeps selecting one
/// repository from a larger bundle from silently changing the wizard's choice.
pub fn create_bundle_from_sources(
    sources: &[String],
) -> std::result::Result<QuickBundleCreation, QuickBundleFailure> {
    let (config, bundle_id) = Config::update(|config| {
        let previous = config.bundles.clone();
        let id = create_bundle_from_sources_in_config(config, sources)
            .map_err(|error| anyhow::Error::new(QuickBundleFailure::InvalidSource(error)))?;
        if let Some(old) = previous.get(&id)
            && config.bundles.get(&id) != Some(old)
        {
            let accepted = crate::project_catalog::snapshot(
                old,
                &targets::CancellableProcessExecutor::with_timeout(std::time::Duration::from_secs(
                    15,
                )),
                true,
            )?;
            crate::database::store_catalog_project(&id, &accepted, true)?;
        }
        let project = crate::project_catalog::snapshot(
            config
                .bundles
                .get(&id)
                .context("created project is missing")?,
            &targets::CancellableProcessExecutor::with_timeout(std::time::Duration::from_secs(15)),
            false,
        )?;
        let canonical = crate::database::store_catalog_project(&id, &project, true)?;
        if canonical != id {
            let mut saved = crate::database::read_project_catalog()?
                .projects
                .into_iter()
                .find(|entry| entry.bundle_id == canonical)
                .context("canonical project is missing")?
                .project;
            for repository in &mut saved.bundle.repositories {
                let identity = saved
                    .identities
                    .get(&repository.id)
                    .context("canonical repository identity is missing")?;
                if let Some(source) = project.bundle.repositories.iter().find(|source| {
                    project.identities.get(&source.id) == Some(identity)
                        && source.destination == repository.destination
                }) {
                    repository.local = source.local.clone();
                    repository.github = source.github.clone();
                }
            }
            config
                .bundles
                .insert(canonical.clone(), saved.bundle.clone());
            config.bundles.remove(&id);
            crate::database::store_catalog_project(&canonical, &saved, true)?;
        }
        Ok(canonical)
    })
    .map_err(|error| {
        error
            .downcast::<QuickBundleFailure>()
            .unwrap_or_else(QuickBundleFailure::Persistence)
    })?;
    Ok(QuickBundleCreation { config, bundle_id })
}

/// Remove a saved project from the config. Only the config entry goes: no
/// checkout, clone or file is touched. Refused while any session still uses
/// the project, checked against fresh state so a dashboard's stale view
/// cannot remove a project a new session just started with.
pub fn remove_bundle(bundle_id: &str) -> Result<Config> {
    let state = crate::database::load_state()?;
    if let Some(refusal) = state.bundle_removal_refusal(bundle_id) {
        bail!(refusal);
    }
    let (config, ()) = Config::update(|config| {
        ensure!(
            config.bundles.remove(bundle_id).is_some(),
            "project {bundle_id:?} is no longer saved"
        );
        config.validate()
    })?;
    crate::database::hide_catalog_project(bundle_id)?;
    Ok(config)
}

/// Add a bundle for all `sources` to an already-loaded config. The source
/// interpretation is shared with the persisted [`create_bundle_from_sources`]
/// entry point and the legacy quick-bundle helper.
pub fn create_bundle_from_sources_in_config(
    config: &mut Config,
    sources: &[String],
) -> Result<String> {
    let sources = sources
        .iter()
        .map(|source| interpret_repository_source(source))
        .collect::<Result<Vec<_>>>()?;
    if sources.is_empty() {
        bail!("at least one repository source is required");
    }

    let mut identities = BTreeSet::new();
    for source in &sources {
        if !identities.insert(source.identity()) {
            bail!("duplicate repository source {:?}", source.display_name);
        }
    }

    if let Some(existing) = exact_configured_bundle(config, &sources)? {
        let bundle = config
            .bundles
            .get_mut(&existing)
            .expect("matched project exists");
        // Local selection carries its own fetch/push settings. Keep the saved
        // repository IDs and layout; earlier sessions hold accepted snapshots.
        for repository in &mut bundle.repositories {
            let Some(identity) =
                crate::import::configured_repository_identity_for_lookup(&existing, repository)
            else {
                continue;
            };
            if let Some(source) = sources.iter().find(|source| {
                source.identity == identity && matches!(source.kind, RepositorySourceKind::Local(_))
            }) && let RepositorySourceKind::Local(root) = &source.kind
            {
                repository.local = Some(root.clone());
                repository.github = None;
            }
        }
        return Ok(existing);
    }

    // Build and validate a candidate before replacing the caller's config, so
    // a later validation error cannot leave an in-memory partial mutation.
    let mut updated = config.clone();
    let mut used_repository_ids = BTreeSet::new();
    let mut repositories = Vec::with_capacity(sources.len());
    for source in sources {
        let base = setup_style_id(&source.name);
        let repository_id = unique_id(&base, |candidate| used_repository_ids.contains(candidate));
        used_repository_ids.insert(repository_id.clone());
        repositories.push(source.into_project_repository(repository_id));
    }
    let primary_repo = repositories
        .first()
        .map(|repository| repository.id.clone())
        .context("at least one repository source is required")?;
    let bundle_id = unique_id(&primary_repo, |candidate| {
        updated.bundles.contains_key(candidate)
    });
    updated.bundles.insert(
        bundle_id.clone(),
        ProjectBundle {
            primary_repo,
            repositories,
        },
    );
    updated.validate()?;
    *config = updated;
    Ok(bundle_id)
}

#[derive(Debug, Clone)]
enum RepositorySourceKind {
    Github(crate::setup::GithubRepository),
    Local(PathBuf),
}

#[derive(Debug, Clone)]
struct InterpretedRepositorySource {
    display_name: String,
    name: String,
    kind: RepositorySourceKind,
    identity: RepositoryIdentity,
}

impl InterpretedRepositorySource {
    fn identity(&self) -> RepositoryIdentity {
        self.identity.clone()
    }

    fn into_project_repository(self, id: String) -> ProjectRepository {
        let (github, local) = match self.kind {
            RepositorySourceKind::Github(repository) => (
                Some(format!("{}/{}", repository.owner, repository.repository)),
                None,
            ),
            RepositorySourceKind::Local(root) => (None, Some(root)),
        };
        ProjectRepository {
            id: id.clone(),
            github,
            local,
            destination: PathBuf::from(id),
            git_ref: None,
        }
    }
}

/// Interpret a source once, including local Git canonicalization and GitHub
/// parsing, so all creation paths use exactly the same source semantics.
fn interpret_repository_source(source: &str) -> Result<InterpretedRepositorySource> {
    let source = source.trim();
    if source.is_empty() {
        bail!("repository source cannot be empty");
    }
    let expanded = mj_core::path_input::expand_local(Path::new(source))?;
    let candidate = expanded.as_path();
    if candidate.exists() {
        let resolved = mj_core::repository::resolve_directory(
            candidate,
            None,
            &mj_core::targets::CancellableProcessExecutor::with_timeout(
                std::time::Duration::from_secs(8),
            ),
        )?;
        let identity = resolved.identity;
        let name = identity.name();
        return Ok(InterpretedRepositorySource {
            display_name: source.to_owned(),
            name,
            identity,
            kind: RepositorySourceKind::Local(resolved.checkout_root),
        });
    }
    if candidate.is_absolute() || source.starts_with('.') || source.starts_with('~') {
        bail!("local repository path {source:?} does not exist");
    }
    let repository = github_repository_from_origin(source).context(format!(
        "{source:?} is not a GitHub owner/repository or URL"
    ))?;
    Ok(InterpretedRepositorySource {
        display_name: source.to_owned(),
        name: repository.repository.clone(),
        identity: RepositoryIdentity::Github(
            repository.owner.to_ascii_lowercase(),
            repository.repository.to_ascii_lowercase(),
        ),
        kind: RepositorySourceKind::Github(repository),
    })
}

fn exact_configured_bundle(
    config: &Config,
    requested: &[InterpretedRepositorySource],
) -> Result<Option<String>> {
    let primary = requested
        .first()
        .context("no repository sources")?
        .identity();
    let mut used = BTreeSet::new();
    let requested_layout = requested
        .iter()
        .map(|source| {
            let id = unique_id(&setup_style_id(&source.name), |id| used.contains(id));
            used.insert(id.clone());
            (source.identity(), PathBuf::from(id))
        })
        .collect::<BTreeSet<_>>();
    for (id, bundle) in &config.bundles {
        if bundle.repositories.len() != requested.len()
            || bundle
                .repositories
                .iter()
                .any(|repository| repository.git_ref.is_some())
        {
            continue;
        }
        let identity_results = bundle
            .repositories
            .iter()
            .map(|repo| crate::import::configured_repository_identity_for_lookup(id, repo))
            .collect::<Vec<_>>();
        if identity_results.iter().any(Option::is_none) {
            continue;
        }
        let identities = identity_results.into_iter().flatten().collect::<Vec<_>>();
        let layout = bundle
            .repositories
            .iter()
            .zip(&identities)
            .map(|(repository, identity)| (identity.clone(), repository.destination.clone()))
            .collect::<BTreeSet<_>>();
        let Some(primary_index) = bundle
            .repositories
            .iter()
            .position(|repository| repository.id == bundle.primary_repo)
        else {
            continue;
        };
        if layout == requested_layout && identities.get(primary_index) == Some(&primary) {
            return Ok(Some(id.clone()));
        }
    }
    Ok(None)
}

fn unique_id(base: &str, mut is_used: impl FnMut(&str) -> bool) -> String {
    if !is_used(base) {
        return base.to_owned();
    }
    for suffix in 2_u32.. {
        let suffix = format!("-{suffix}");
        let prefix_len = 64usize.saturating_sub(suffix.len());
        let prefix = base.chars().take(prefix_len).collect::<String>();
        let candidate = format!("{prefix}{suffix}");
        if !is_used(&candidate) {
            return candidate;
        }
    }
    unreachable!("u32 repository/bundle id suffixes exhausted")
}

pub struct SessionLaunchOptions {
    pub create_managed_worktree: Option<bool>,
    /// Full commit ID to start the bundle's primary repository at.
    pub at: Option<String>,
    /// With `at`, the new branch created there; otherwise an existing branch.
    pub branch: Option<String>,
    /// Diff base; defaults to `at`.
    pub base: Option<String>,
    pub subagents: Option<mj_core::subagent::SubagentPolicy>,
    /// Turn review for this session; `None` follows `[review]`.
    pub review: Option<mj_core::config::SessionReview>,
    pub initial_prompt: Option<String>,
    pub workspace_id: String,
    pub additional_mounts: Vec<AdditionalMount>,
    pub resource_allocation: Option<SessionResourceAllocation>,
    pub project_directory: Option<PathBuf>,
    pub session_title_override: Option<String>,
}

pub struct SessionResumeOptions {
    pub additional_mounts: Option<Vec<AdditionalMount>>,
    pub resource_allocation: Option<SessionResourceAllocation>,
    pub discard_queue: bool,
}

fn selected_host_container_size(
    template: &TargetTemplate,
    allocation: Option<&SessionResourceAllocation>,
) -> Option<(String, HostContainerSize)> {
    let host = container_size_host(template)?;
    let SessionResourceAllocation::Container { cpus, memory_bytes } = allocation? else {
        return None;
    };
    Some((
        host.to_owned(),
        HostContainerSize {
            cpus: *cpus,
            memory_bytes: *memory_bytes,
        },
    ))
}

impl Controller {
    pub fn load() -> Result<Self> {
        // A configuration the person has to fix, such as an entry whose secret
        // is missing, is the reason a request fails, not an internal error.
        let config = Config::load().map_err(|error| {
            let refusal = mj_core::refusal::Refusal::precondition(format!("{error:#}"));
            error.context(refusal)
        })?;
        let state = crate::database::load_state()?;
        Ok(Self { config, state })
    }

    /// Startup-only traversal for legacy metadata and configuration diagnostics.
    /// Ordinary readers consume the writer's committed snapshot directly.
    pub(crate) fn prepare_persisted_sessions(&mut self) -> Result<()> {
        // Missing session dependencies must not lock users out of the tools
        // needed to repair them. Operations validate the session they act on.
        self.state.validate()?;
        for session in self.state.sessions.values() {
            if let Some(issue) = session.configuration_issue(&self.config) {
                tracing::warn!(session_id = %session.id, "{issue}");
            }
        }
        self.backfill_target_runtime()
    }

    pub fn reload(&mut self) -> Result<()> {
        // Capture legacy settings from the previous config before a manual
        // edit removes them. Only fill missing metadata, never overwrite it.
        self.backfill_target_runtime()?;
        *self = Self::load()?;
        Ok(())
    }

    fn backfill_target_runtime(&mut self) -> Result<()> {
        let missing: Vec<_> = self
            .state
            .sessions
            .values()
            .filter(|session| session.target_runtime.is_none())
            .map(|session| session.id.clone())
            .collect();
        for id in missing {
            let session = self.state.sessions.get_mut(&id).expect("collected session");
            match session.target_runtime_settings(&self.config) {
                Ok(runtime) => {
                    let runtime = runtime.into_owned();
                    session.target_runtime = crate::database::backfill_target_runtime(
                        &session.id,
                        &session.target_template_id,
                        &runtime,
                    )?;
                }
                Err(error) => {
                    tracing::warn!(session_id = %session.id, %error, "target access needs configuration repair")
                }
            }
        }
        Ok(())
    }

    fn persist_session_state(&self, session_id: &str) -> Result<()> {
        match self.state.sessions.get(session_id) {
            Some(session) => crate::database::save_lifecycle_session(session),
            None => crate::database::delete_session(session_id),
        }
    }

    fn persist_session_transition_or_restore(
        &mut self,
        session_id: &str,
        previous: &SessionRecord,
        context: &'static str,
    ) -> Result<()> {
        persist_session_record_transition_or_restore(
            &mut self.state,
            session_id,
            previous,
            context,
            &crate::database::save_lifecycle_session,
        )
    }

    fn restore_prior_session_after_persistence_failure(
        &mut self,
        session_id: &str,
        previous: &SessionRecord,
        primary: anyhow::Error,
    ) -> anyhow::Error {
        restore_session_after_persistence_failure(
            &mut self.state,
            session_id,
            previous,
            primary,
            crate::database::save_lifecycle_session,
        )
    }

    /// Resolve an entered path on its owning host. Call only from background work.
    pub fn resolve_input_path(
        &self,
        target_id: &str,
        path: &Path,
        executor: &impl CommandExecutor,
    ) -> Result<PathBuf> {
        let target = self
            .config
            .targets
            .get(target_id)
            .context("Unknown path target")?;
        resolve_target_input_path(target, path, executor)
    }

    /// Verify a mount source on the host where Mjolnir will consume it, and report
    /// the filesystem reason it must be attached read-only, if there is one.
    ///
    /// The probe runs in the same round trip as the existence check so the
    /// editor learns both answers without a second wait. A probe that cannot
    /// answer reports no reason: provisioning decides that authoritatively.
    pub fn validate_mount_source(
        &self,
        target_id: &str,
        source: &Path,
        executor: &impl CommandExecutor,
    ) -> Result<Option<String>> {
        let target = self
            .config
            .targets
            .get(target_id)
            .with_context(|| format!("unknown target template {target_id:?}"))?;
        let exists = match target {
            TargetTemplate::LocalPodman { .. }
            | TargetTemplate::LocalDocker { .. }
            | TargetTemplate::AppleContainer { .. }
            | TargetTemplate::AwsEc2 { .. } => std::fs::metadata(source)
                .map(|metadata| metadata.is_dir())
                .or_else(|error| {
                    if error.kind() == std::io::ErrorKind::NotFound {
                        Ok(false)
                    } else {
                        Err(error)
                    }
                })
                .with_context(|| format!("inspect resource source {}", source.display()))?,
            TargetTemplate::SshPodman { ssh, .. } | TargetTemplate::SshDocker { ssh, .. } => {
                targets::ssh_directory_exists(&SshTarget::from(ssh), source, executor)?
            }
            TargetTemplate::LocalBare | TargetTemplate::SshBare { .. } => {
                bail!("resource attachments are unsupported for bare targets")
            }
        };
        ensure!(
            exists,
            "source path {} does not exist or is not a directory",
            source.display()
        );
        Ok(self.forced_read_only_reason(target, source, executor))
    }

    /// The `filesystem (reason)` label for a source the runtime cannot overlay.
    fn forced_read_only_reason(
        &self,
        target: &TargetTemplate,
        source: &Path,
        executor: &impl CommandExecutor,
    ) -> Option<String> {
        let ssh = match target {
            TargetTemplate::LocalPodman { .. } | TargetTemplate::LocalDocker { .. } => None,
            TargetTemplate::SshPodman { ssh, .. } | TargetTemplate::SshDocker { ssh, .. } => {
                Some(SshTarget::from(ssh))
            }
            // Apple Container already mounts read-only, and EC2 copies instead
            // of mounting, so neither has an overlay to lose.
            _ => return None,
        };
        if matches!(target, TargetTemplate::LocalDocker { .. })
            && let Ok(Some(_)) = targets::local_docker_vm_share(executor)
        {
            return Some("Docker VM file share (cannot back an overlay)".to_owned());
        }
        let filesystem = targets::probe_filesystem_types(
            ssh.as_ref(),
            std::slice::from_ref(&source.to_path_buf()),
            executor,
        )
        .map_err(|error| {
            tracing::debug!(
                source = %source.display(),
                error = format!("{error:#}"),
                "could not probe the filesystem under a mount source"
            );
        })
        .ok()?
        .pop()?;
        let reason = targets::overlay_unsupported_filesystem(&filesystem)?;
        Some(format!("{filesystem} ({reason})"))
    }

    fn fail_new_session_with_cleanup(
        &mut self,
        session_id: &str,
        error: anyhow::Error,
        executor: &impl CommandExecutor,
    ) -> Result<anyhow::Error> {
        let original = provisioning::note_new_session_launch_failure(session_id, &error);
        let cleanup_error = self
            .cleanup_new_session_worktree_after_failure(session_id, executor)
            .err()
            .map(|cleanup_error| format!("{cleanup_error:#}"));
        if let Some(cleanup_error) = &cleanup_error {
            tracing::warn!(
                session_id,
                error = %cleanup_error,
                "new-session worktree rollback reported a cleanup failure"
            );
        }
        let failure = apply_failed_new_session_rollback(
            &mut self.state,
            session_id,
            &original,
            cleanup_error,
        );
        self.persist_session_state(session_id)?;
        Ok(failure)
    }

    pub fn register_session_with_resources(
        &mut self,
        profile_id: &str,
        bundle_id: &str,
        target_id: &str,
        title: impl Into<String>,
        options: SessionLaunchOptions,
    ) -> Result<String> {
        self.register_session_with_executor(
            profile_id,
            bundle_id,
            target_id,
            title,
            options,
            &targets::CancellableProcessExecutor::with_timeout(std::time::Duration::from_secs(15)),
        )
    }

    fn register_session_with_executor(
        &mut self,
        profile_id: &str,
        bundle_id: &str,
        target_id: &str,
        title: impl Into<String>,
        options: SessionLaunchOptions,
        executor: &impl CommandExecutor,
    ) -> Result<String> {
        let SessionLaunchOptions {
            create_managed_worktree,
            at,
            branch,
            base,
            subagents,
            review,
            initial_prompt,
            workspace_id,
            additional_mounts,
            resource_allocation,
            project_directory,
            session_title_override,
        } = options;
        let launch_base = match base {
            Some(base) => {
                let base = base.trim();
                if base.is_empty() {
                    bail!("`base` must not be empty");
                }
                Some(base.to_owned())
            }
            None => None,
        };
        let branch = match branch {
            Some(branch) => {
                let branch = branch.trim();
                ensure!(!branch.is_empty(), "`branch` must not be empty");
                Some(branch.to_owned())
            }
            None => None,
        };
        if launch_base.is_some() && create_managed_worktree == Some(false) {
            bail!("`base` requires a managed worktree or a bundle session");
        }
        let session_title_override = match session_title_override {
            Some(title) => {
                Some(normalize_session_title(&title).context("session name cannot be empty")?)
            }
            None => None,
        };
        let profile = self
            .config
            .profiles
            .get(profile_id)
            .with_context(|| format!("unknown profile {profile_id:?}"))?;
        ensure!(profile.enabled, "profile {profile_id:?} is disabled");
        let template = self
            .config
            .targets
            .get(target_id)
            .with_context(|| format!("unknown target template {target_id:?}"))?;
        if create_managed_worktree == Some(true) && !is_bare_project_target(template) {
            bail!("managed worktree creation requires a bare Git project");
        }
        if project_directory.is_some() != is_bare_project_target(template) {
            bail!("raw project directories require a bare target, and bare targets require one");
        }
        if let Some(path) = &project_directory
            && (!path.is_absolute()
                || path
                    .components()
                    .any(|part| part == std::path::Component::ParentDir))
        {
            bail!("bare project directory must be an absolute safe path");
        }
        let bundle = project_directory
            .is_none()
            .then(|| self.config.bundles.get(bundle_id))
            .flatten();
        if project_directory.is_none() && bundle.is_none() {
            bail!("unknown bundle {bundle_id:?}");
        }
        // `at` becomes an exact checkout of the bundle's primary repository,
        // which then owns the branch. Without it, the branch is an existing
        // one to check out.
        let (checkout, launch_branch) = match at {
            Some(at) => {
                let bundle = bundle.context("`at` requires a bundle-backed session")?;
                ensure!(
                    create_managed_worktree != Some(false),
                    "`at` requires an isolated workspace"
                );
                let mut checkout = mj_core::remote_git::ExactCheckout {
                    repository_id: bundle.primary_repo.clone(),
                    commit: at.trim().to_owned(),
                    branch,
                };
                checkout.validate()?;
                checkout.commit.make_ascii_lowercase();
                (Some(checkout), None)
            }
            None => (None, branch),
        };
        if profile.kind == mj_core::config::HarnessKind::Muse
            && (!additional_mounts.is_empty()
                || bundle.is_some_and(|bundle| bundle.repositories.len() > 1))
        {
            bail!(
                "{} ACP supports one workspace root; use a single-repository bundle without attached directories",
                profile.kind.display_name()
            );
        }
        let (bundle_id, project) = if let Some(bundle) = bundle {
            let project = crate::project_catalog::snapshot(bundle, executor, true)?;
            let canonical = crate::database::store_catalog_project(bundle_id, &project, true)?;
            (canonical, Some(project))
        } else if let Some(directory) = project_directory.as_deref() {
            let git = match template {
                TargetTemplate::LocalBare => {
                    executor
                        .execute(
                            &targets::CommandSpec::new(
                                "git",
                                [
                                    "-C",
                                    &directory.to_string_lossy(),
                                    "rev-parse",
                                    "--is-inside-work-tree",
                                ],
                            )
                            .purpose("inspect raw project repository"),
                        )?
                        .status
                        == 0
                }
                _ => true,
            };
            if git {
                let (id, project) =
                    crate::project_catalog::accept_directory(template, directory, executor)?;
                (id, Some(project))
            } else {
                (bundle_id.to_owned(), None)
            }
        } else {
            (bundle_id.to_owned(), None)
        };
        validate_resource_allocation(template, resource_allocation.as_ref())?;
        let selected_container_size =
            selected_host_container_size(template, resource_allocation.as_ref());
        if !additional_mounts.is_empty() && mount_history_host(template).is_none() {
            bail!("attached resources are unsupported for this target");
        }
        targets::validate_additional_mounts(&additional_mounts)?;
        let id = new_session_id()?;
        let now = now();
        let record = SessionRecord {
            project,
            target_runtime: Some(template.into()),
            build_cache: None,
            create_managed_worktree,
            launch_base,
            launch_branch,
            checkout,
            publication: None,
            subagents: Some(subagents.unwrap_or_else(|| profile.subagents.clone())),
            archived: false,
            container_cpus: None,
            container_memory: None,
            // Recorded for every new session, container-backed or not, so a
            // later move into a container already knows the path its checkout
            // will occupy. Only sessions that predate per-session container
            // workspaces leave it unset.
            container_workspace: Some(targets::new_container_workspace(&id)?),
            id: id.clone(),
            workspace_id,
            title: title.into(),
            harness_kind: profile.kind,
            last_profile: profile_id.to_string(),
            bundle_id,
            project_directory,
            managed_worktree: None,
            review,
            target_template_id: target_id.to_string(),
            resource_allocation,
            additional_mounts: additional_mounts.clone(),
            state: SessionState::Provisioning,
            target: None,
            native_session_id: None,
            acp_session_title: None,
            session_title_override,
            created_at: now.clone(),
            updated_at: now,
            viewed_through_event_ordinal: 0,
            draft_input: initial_prompt.unwrap_or_default(),
            last_error: None,
            last_checkpoint_error: None,
            checkpoint: None,
        };
        // Creation authors the whole record, so it writes the whole row. The
        // record reaches memory only once it is durable: a session this process
        // alone knows about is one the database can never resume or clean up.
        crate::database::save_new_session(&record, selected_container_size.clone())?;
        if record.harness_kind.supports_delegation_tools() {
            self.state.last_subagent_policy = record.subagents.clone().unwrap_or_default();
        }
        self.state.sessions.insert(id.clone(), record);
        if let Some((host, size)) = selected_container_size {
            self.state.remember_container_size(&host, size);
        }
        if let Some(host) = mount_history_host(template) {
            // Mount history only seeds the attach dialog's suggestions. The
            // session row is already committed, so a failed suggestion write is
            // reported rather than turned into a failed registration.
            match crate::database::remember_mount_sources(host, &additional_mounts) {
                Ok(()) => self.state.remember_mount_sources(host, &additional_mounts),
                Err(error) => tracing::warn!(
                    session_id = id,
                    error = format!("{error:#}"),
                    "could not remember the attached resource directories for later suggestions"
                ),
            }
        }
        Ok(id)
    }

    pub fn rename_session(&mut self, session_id: &str, title: &str) -> Result<String> {
        let title = normalize_session_title(title).context("session name cannot be empty")?;
        ensure!(
            self.state.sessions.contains_key(session_id),
            "unknown session {session_id}"
        );
        let updated_at = now();
        crate::database::set_session_title_override(session_id, &title, &updated_at)?;
        let record = self
            .state
            .sessions
            .get_mut(session_id)
            .expect("session was checked before updating its title");
        record.session_title_override = Some(title.clone());
        record.updated_at = updated_at;
        Ok(title)
    }

    /// Move a session, and the sub-agents under it, to another workspace.
    /// Returns how many sessions moved.
    pub fn set_session_workspace(&mut self, session_id: &str, workspace_id: &str) -> Result<usize> {
        ensure!(
            self.state.sessions.contains_key(session_id),
            "unknown session {session_id}"
        );
        let mut ids = vec![session_id.to_owned()];
        ids.extend(
            self.state
                .subagents
                .values()
                .filter(|child| child.parent_session_id == session_id)
                .map(|child| child.child_session_id.clone()),
        );
        crate::database::set_sessions_workspace(&ids, workspace_id)?;
        for id in &ids {
            if let Some(record) = self.state.sessions.get_mut(id) {
                record.workspace_id = workspace_id.to_owned();
            }
        }
        Ok(ids.len())
    }

    pub fn rename_profile_id(&mut self, old_id: &str, new_id: &str) -> Result<()> {
        mj_core::config::validate_id("profile", new_id)?;
        if old_id == new_id {
            ensure!(
                self.config.profiles.contains_key(old_id),
                "unknown profile {old_id:?}"
            );
            return Ok(());
        }
        let journal = ConfigRenameJournal {
            kind: ConfigRenameKind::Profile,
            old_id: old_id.to_owned(),
            new_id: new_id.to_owned(),
        };
        write_config_rename_journal(&journal)?;
        let (config, ()) = match Config::update(|config| {
            ensure!(
                config.profiles.contains_key(old_id),
                "unknown profile {old_id:?}"
            );
            ensure!(
                !config.profiles.contains_key(new_id),
                "profile {new_id:?} already exists"
            );
            let profile = config
                .profiles
                .remove(old_id)
                .expect("profile was checked in the transaction");
            config.profiles.insert(new_id.to_owned(), profile);
            Ok(())
        }) {
            Ok(result) => result,
            Err(error) => {
                remove_config_rename_journal()
                    .context("remove profile rename journal after config save failed")?;
                return Err(error).context("save renamed profile configuration");
            }
        };
        self.config = config;
        mj_core::test_hooks::reach_test_hook("config_replacement_before_reference_migration")?;
        if let Err(error) = crate::database::rename_profile_references(old_id, new_id) {
            let restore = Config::update(|config| {
                let profile = config
                    .profiles
                    .remove(new_id)
                    .with_context(|| format!("renamed profile {new_id:?} is missing"))?;
                ensure!(
                    !config.profiles.contains_key(old_id),
                    "cannot restore profile rename: both {old_id:?} and {new_id:?} exist"
                );
                config.profiles.insert(old_id.to_owned(), profile);
                Ok(())
            });
            let restored = match restore {
                Ok((config, ())) => config,
                Err(restore_error) => {
                    return Err(error).context(format!(
                        "rename profile references; additionally failed to restore config: {restore_error:#}"
                    ));
                }
            };
            self.config = restored;
            if let Err(restore_error) = remove_config_rename_journal() {
                return Err(error).context(format!(
                    "rename profile references; additionally failed to remove rename journal: {restore_error:#}"
                ));
            }
            return Err(error).context("rename profile references");
        }
        let affected: Vec<_> = self
            .state
            .sessions
            .values()
            .filter(|session| session.last_profile == old_id)
            .map(|session| session.id.clone())
            .collect();
        for id in affected {
            self.state
                .sessions
                .get_mut(&id)
                .expect("collected session")
                .last_profile = new_id.to_owned();
        }
        remove_config_rename_journal()?;
        Ok(())
    }

    pub fn rename_target_id(&mut self, old_id: &str, new_id: &str) -> Result<()> {
        mj_core::config::validate_id("target template", new_id)?;
        if old_id == new_id {
            ensure!(
                self.config.targets.contains_key(old_id),
                "unknown target {old_id:?}"
            );
            return Ok(());
        }
        let journal = ConfigRenameJournal {
            kind: ConfigRenameKind::Target,
            old_id: old_id.to_owned(),
            new_id: new_id.to_owned(),
        };
        write_config_rename_journal(&journal)?;
        let (config, ()) = match Config::update(|config| {
            ensure!(
                config.targets.contains_key(old_id),
                "unknown target {old_id:?}"
            );
            ensure!(
                !config.targets.contains_key(new_id),
                "target {new_id:?} already exists"
            );
            let target = config
                .targets
                .remove(old_id)
                .expect("target was checked in the transaction");
            config.targets.insert(new_id.to_owned(), target);
            Ok(())
        }) {
            Ok(result) => result,
            Err(error) => {
                remove_config_rename_journal()
                    .context("remove target rename journal after config save failed")?;
                return Err(error).context("save renamed target configuration");
            }
        };
        self.config = config;
        mj_core::test_hooks::reach_test_hook("config_replacement_before_reference_migration")?;
        if let Err(error) = crate::database::rename_target_references(old_id, new_id) {
            let restore = Config::update(|config| {
                let target = config
                    .targets
                    .remove(new_id)
                    .with_context(|| format!("renamed target {new_id:?} is missing"))?;
                ensure!(
                    !config.targets.contains_key(old_id),
                    "cannot restore target rename: both {old_id:?} and {new_id:?} exist"
                );
                config.targets.insert(old_id.to_owned(), target);
                Ok(())
            });
            let restored = match restore {
                Ok((config, ())) => config,
                Err(restore_error) => {
                    return Err(error).context(format!(
                        "rename target references; additionally failed to restore config: {restore_error:#}"
                    ));
                }
            };
            self.config = restored;
            if let Err(restore_error) = remove_config_rename_journal() {
                return Err(error).context(format!(
                    "rename target references; additionally failed to remove rename journal: {restore_error:#}"
                ));
            }
            return Err(error).context("rename target references");
        }
        let affected: Vec<_> = self
            .state
            .sessions
            .values()
            .filter(|session| session.target_template_id == old_id)
            .map(|session| session.id.clone())
            .collect();
        for id in affected {
            self.state
                .sessions
                .get_mut(&id)
                .expect("collected session")
                .target_template_id = new_id.to_owned();
        }
        remove_config_rename_journal()?;
        Ok(())
    }

    /// Finish a profile/target id rename interrupted between the atomic config
    /// replacement and SQLite transaction. Each step is idempotent, so a
    /// second crash leaves the same intent available for the next startup.
    pub fn recover_config_id_rename() -> Result<bool> {
        let path = config_rename_journal_path();
        let body = match fs::read(&path) {
            Ok(body) => body,
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Ok(false),
            Err(error) => return Err(error).context(format!("read {}", path.display())),
        };
        let journal: ConfigRenameJournal =
            serde_json::from_slice(&body).with_context(|| format!("parse {}", path.display()))?;
        match journal.kind {
            ConfigRenameKind::Profile => {
                Config::update(|config| {
                    finish_config_map_rename(
                        &mut config.profiles,
                        &journal.old_id,
                        &journal.new_id,
                        "profile",
                    )?;
                    Ok(())
                })?;
                crate::database::rename_profile_references(&journal.old_id, &journal.new_id)?;
            }
            ConfigRenameKind::Target => {
                // The file's own entries, not `Config::update`'s view: that one
                // adds the standard local targets, so after a built-in id such
                // as `localhost` was renamed away, its default would reappear
                // beside the new id and read as a rename that cannot finish.
                Config::update_to(&mj_core::config::config_path(), |config| {
                    finish_config_map_rename(
                        &mut config.targets,
                        &journal.old_id,
                        &journal.new_id,
                        "target",
                    )?;
                    Ok(())
                })?;
                crate::database::rename_target_references(&journal.old_id, &journal.new_id)?;
            }
        }
        remove_config_rename_journal()?;
        Ok(true)
    }

    /// Record the per-session container size overrides and attached
    /// directories. Nothing is applied to a running container: the values are
    /// read the next time the session's container is created.
    pub fn update_session_container_settings(
        &mut self,
        session_id: &str,
        cpus: Option<String>,
        memory: Option<String>,
        additional_mounts: Vec<targets::AdditionalMount>,
        mount_history: Vec<std::path::PathBuf>,
        executor: &impl CommandExecutor,
    ) -> Result<()> {
        let session = self
            .state
            .sessions
            .get(session_id)
            .with_context(|| format!("unknown session {session_id}"))?;
        // A directory the runtime cannot find is created by Docker, owned by
        // root, when the container is recreated (launch finding J-24). Check
        // each newly attached source where the container will read it: on
        // this host for a local runtime, over the machine's connection for an
        // SSH one. A directory already attached was checked when it was
        // added, and a size change must not fail because it has since gone.
        for mount in &additional_mounts {
            if session
                .additional_mounts
                .iter()
                .any(|attached| attached.source == mount.source)
            {
                continue;
            }
            self.validate_mount_source(&session.target_template_id, &mount.source, executor)?;
        }
        let cpus = cpus.filter(|value| !value.trim().is_empty());
        let memory = memory.filter(|value| !value.trim().is_empty());
        let updated_at = now();
        crate::database::set_session_container_settings(
            session_id,
            cpus.as_deref(),
            memory.as_deref(),
            &additional_mounts,
            &updated_at,
        )?;
        if let Some(host) = self
            .config
            .targets
            .get(
                &self.state.sessions[session_id]
                    .target_template_id
                    .to_owned(),
            )
            .and_then(mj_core::config::mount_history_host)
        {
            let host = host.to_owned();
            // The dialog owns the suggestion list, so forgetting a directory
            // there has to survive the mounts being remembered right after.
            crate::database::replace_mount_history(&host, &mount_history)?;
            crate::database::remember_mount_sources(&host, &additional_mounts)?;
            self.state.mount_history.insert(host.clone(), mount_history);
            self.state.remember_mount_sources(&host, &additional_mounts);
        }
        let record = self
            .state
            .sessions
            .get_mut(session_id)
            .expect("session was checked before updating its container settings");
        record.container_cpus = cpus;
        record.container_memory = memory;
        record.additional_mounts = additional_mounts;
        record.updated_at = updated_at;
        Ok(())
    }
}

fn config_rename_journal_path() -> PathBuf {
    data_dir().join(CONFIG_RENAME_JOURNAL)
}

fn write_config_rename_journal(journal: &ConfigRenameJournal) -> Result<()> {
    let path = config_rename_journal_path();
    let body = serde_json::to_vec(journal).context("serialize config rename journal")?;
    atomic_write(&path, &body).with_context(|| format!("write {}", path.display()))
}

fn remove_config_rename_journal() -> Result<()> {
    let path = config_rename_journal_path();
    match fs::remove_file(&path) {
        Ok(()) => Ok(()),
        Err(error) if error.kind() == std::io::ErrorKind::NotFound => Ok(()),
        Err(error) => Err(error).with_context(|| format!("remove {}", path.display())),
    }
}

fn finish_config_map_rename<T>(
    entries: &mut BTreeMap<String, T>,
    old_id: &str,
    new_id: &str,
    kind: &str,
) -> Result<()> {
    if let Some(entry) = entries.remove(old_id) {
        ensure!(
            !entries.contains_key(new_id),
            "cannot recover {kind} rename: both {old_id:?} and {new_id:?} exist"
        );
        entries.insert(new_id.to_owned(), entry);
    } else {
        ensure!(
            entries.contains_key(new_id),
            "cannot recover {kind} rename: neither {old_id:?} nor {new_id:?} exists"
        );
    }
    Ok(())
}

/// Where this session's harness reads and writes its profile inside the target.
///
/// This is the per-session root [`removable_profile_root`] names, on every
/// target: a session always runs from a staged copy of its profile, never from
/// the profile home itself. A harness with a nested home keeps its state in a
/// subdirectory of the root named after it, the leaf its XDG configuration
/// directory must have.
#[cfg(test)]
pub(crate) fn target_profile_home_for_test(
    locator: &targets::TargetLocator,
    session_id: &str,
    profile: &mj_core::config::HarnessProfile,
) -> String {
    target_profile_home(locator, session_id, profile)
}

fn target_profile_home(
    locator: &targets::TargetLocator,
    session_id: &str,
    profile: &mj_core::config::HarnessProfile,
) -> String {
    let root = removable_profile_root(locator, session_id, profile);
    if profile.kind.nested_home() {
        PathBuf::from(root)
            .join(profile.kind.id())
            .to_string_lossy()
            .into_owned()
    } else {
        root
    }
}

/// The per-session profile directory a session's harness home lives in, which
/// the session owns and an in-place harness replacement or teardown may delete.
///
/// This is the root that [`target_profile_home`] derives its answer from, not
/// that answer itself: a harness with an XDG-nested home keeps its home in a
/// subdirectory of a per-session root under the data directory, and the whole
/// root is what belongs to the session.
pub(super) fn removable_profile_root(
    locator: &targets::TargetLocator,
    session_id: &str,
    profile: &mj_core::config::HarnessProfile,
) -> String {
    match locator {
        targets::TargetLocator::LocalBare { .. } if profile.kind.nested_home() => {
            targets::local_nested_profile_root(session_id)
                .to_string_lossy()
                .into_owned()
        }
        targets::TargetLocator::LocalBare { worker_root } => Path::new(worker_root)
            .join("profile")
            .to_string_lossy()
            .into_owned(),
        targets::TargetLocator::LocalPodman { .. }
        | targets::TargetLocator::LocalDocker { .. }
        | targets::TargetLocator::AppleContainer { .. }
        | targets::TargetLocator::SshPodman { .. }
        | targets::TargetLocator::SshDocker { .. } => {
            format!("/var/lib/hel/profiles/{session_id}")
        }
        targets::TargetLocator::AwsEc2 { .. } | targets::TargetLocator::SshBare { .. } => {
            format!(".local/share/hel/profiles/{session_id}")
        }
    }
}

/// Resolve the login home on the machine that owns an editable path.
pub fn resolve_target_input_path(
    target: &TargetTemplate,
    path: &Path,
    executor: &impl CommandExecutor,
) -> Result<PathBuf> {
    if !mj_core::path_input::needs_home(path)? {
        return Ok(path.to_path_buf());
    }
    let host = cache_host::CacheHost::for_path_target(target)?;
    mj_core::path_input::expand_home(path, Some(&host.home(executor)?))
}

/// Resolve the login home on a configured machine, for the Settings screen's
/// path fields. A machine, not a runtime, is what owns a home directory.
pub fn resolve_machine_input_path(
    machine: &mj_core::config::Machine,
    path: &Path,
    executor: &impl CommandExecutor,
) -> Result<PathBuf> {
    if !mj_core::path_input::needs_home(path)? {
        return Ok(path.to_path_buf());
    }
    // An EC2 instance does not exist until a session starts, so the only home
    // this screen can resolve is this machine's.
    let host = cache_host::CacheHost::for_path_machine(machine)?;
    mj_core::path_input::expand_home(path, Some(&host.home(executor)?))
}

fn execute_checked(executor: &impl CommandExecutor, command: CommandSpec) -> Result<CommandOutput> {
    let output = executor.execute(&command)?;
    if output.status != 0 {
        let detail = command_error_detail(&output.stderr);
        if detail.is_empty() {
            bail!("{} failed with status {}", command.purpose, output.status);
        }
        bail!("{detail}");
    }
    Ok(output)
}

fn command_error_detail(stderr: &[u8]) -> String {
    let reported = String::from_utf8_lossy(stderr);
    let reported = reported.trim();
    let detail = reported
        .rsplit_once("\nCaused by:\n")
        .map_or(reported, |(_, causes)| causes);
    let detail = detail.strip_prefix("Error: ").unwrap_or(detail);
    detail
        .lines()
        .map(|line| line.strip_prefix("    ").unwrap_or(line))
        .collect::<Vec<_>>()
        .join("\n")
        .trim()
        .to_owned()
}

fn now() -> String {
    Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Secs, true)
}

fn restore_session_after_persistence_failure(
    state: &mut State,
    session_id: &str,
    previous: &SessionRecord,
    primary: anyhow::Error,
    persist: impl FnOnce(&SessionRecord) -> Result<()>,
) -> anyhow::Error {
    state
        .sessions
        .insert(session_id.to_owned(), previous.clone());
    let restored = state
        .sessions
        .get(session_id)
        .expect("restored session record disappeared");
    match persist(restored) {
        Ok(()) => primary,
        Err(error) => primary.context(format!(
            "restored prior session state in memory, but failed to persist the rollback: {error:#}"
        )),
    }
}

fn persist_session_record_transition_or_restore(
    state: &mut State,
    session_id: &str,
    previous: &SessionRecord,
    context: &'static str,
    persist: &impl Fn(&SessionRecord) -> Result<()>,
) -> Result<()> {
    let result = persist(
        state
            .sessions
            .get(session_id)
            .expect("checkpoint session disappeared before persistence"),
    );
    match result {
        Ok(()) => Ok(()),
        Err(error) => Err(restore_session_after_persistence_failure(
            state,
            session_id,
            previous,
            error.context(context),
            persist,
        )),
    }
}

pub fn config_only_controller(config: Config) -> Controller {
    Controller {
        config,
        state: State::default(),
    }
}

#[cfg(test)]
mod tests;