agent_engine/daemon/

reload.rs

//! `synaps daemon reload` (PLAN-phase3 §2.8, C3): version gate → drain →
//! `Checkpoint{Reload}` every session → reload-state → announce
//! `Reloading`/`Bye{Reloading}` → `execv` self (same pid, adopted flock,
//! CLOEXEC listener) → new image rehydrates sessions from reload-state
//! BEFORE accepting.
//!
//! What reload cannot preserve (§2.8, stated once): in-flight turns
//! (checkpointed = cancelled; partial history + restart marker kept), pending prompts (answered
//! `None`), PTY/background shells (closed, announced), `turn_replay`,
//! input ownership (the owner reclaims it on
//! reconnect via `was_owner`). What it preserves — each session's
//! `Checkpoint{Reload}` reply carries a `SessionReloadRecord`: its journal
//! and id (the rehydrated session continues the same journal), its
//! `SessionConfig` as created (cwd, system, prompt manifest, compaction
//! policy, auto-compact, …), its keep-warm pin, its lifecycle (a Parked
//! session comes back Parked), the non-persisted runtime knobs
//! (`settings_replay`: context window, compaction model, retries,
//! timeouts, tool-output cap, worker grants, `/system`), the CURRENT
//! model/thinking (`/model` mid-session survives), and the session's exact
//! tool activations (pins only, re-validated by the new runtime at its first
//! turn start — `SessionToolSet::restore_carried`).
//!
//! Windows has no `execv`, and a byte-range lock cannot be inherited, so
//! step 5 is a hand-off between two processes (see `daemon::win`): the old
//! image starts the new one with the reload-state and a hand-off event; the
//! new image queues its `daemon.lock` request behind the old one and sets
//! the event; the old image exits — discarding what an exec would — and its
//! release grants the queued request, so the liveness oracle never reads
//! "free". The new image does this before booting anything, then proceeds
//! exactly as after an exec. Same guarantees, one difference: the pid
//! changes (clients learn it from the next `Welcome`).

use std::path::{Path, PathBuf};
use std::sync::atomic::Ordering;
use std::sync::Arc;
use std::time::Duration;

use serde::{Deserialize, Serialize};

use super::registry::{self, DaemonLock, DaemonPaths};
use super::DaemonState;
use crate::session::wire::{ClientFrame, CHECKPOINT_QUERY_ID, PROTOCOL_VERSION};
use crate::session::{
    CheckpointReason, SessionCommand, SessionConfig, SessionEventWire, SessionHandle,
    SessionLifecycle, SessionReloadRecord, SessionSetting,
};

/// Env: path of the reload-state file handed to the new image.
pub const RELOAD_STATE_ENV: &str = "SYNAPS_DAEMON_RELOAD_STATE";
/// Env: inherited `daemon.lock` fd (mandatory when `RELOAD_STATE_ENV` is set).
pub const LOCK_FD_ENV: &str = "SYNAPS_DAEMON_LOCK_FD";
/// Env: the subagent handle counter read at the `execv` itself, later than
/// `ReloadState::next_subagent_id` (written after the checkpoints): a worker
/// that ignored its stop could still dispatch in between.
pub const SUBAGENT_ID_FLOOR_ENV: &str = "SYNAPS_DAEMON_SUBAGENT_ID_FLOOR";
/// Windows: env naming the event the new image sets once its `daemon.lock`
/// request is queued behind the old image (which then exits).
pub const HANDOFF_EVENT_ENV: &str = "SYNAPS_DAEMON_HANDOFF_EVENT";
/// Windows: env carrying the old image's pid; the new image waits for it to
/// be gone (and its pipe instances with it) before it binds.
pub const HANDOFF_PID_ENV: &str = "SYNAPS_DAEMON_HANDOFF_PID";
/// Windows: how long the old image waits for the new one to queue its lock
/// request — process start and reading the reload-state; nothing boots first.
#[cfg(windows)]
const HANDOFF_ARM_TIMEOUT: Duration = Duration::from_secs(15);
/// Windows: how long the new image waits for the old one to let go.
#[cfg(windows)]
const HANDOFF_EXIT_TIMEOUT: Duration = Duration::from_secs(30);
/// Env: default drain budget in seconds.
pub const DRAIN_SECS_ENV: &str = "SYNAPS_DAEMON_RELOAD_DRAIN_SECS";
const DEFAULT_DRAIN: Duration = Duration::from_secs(30);
const VERSION_PROBE_TIMEOUT: Duration = Duration::from_secs(5);
/// Per-session `Checkpoint{Reload}` wait: `cancel_turn` (the drain + its
/// bounded save) + stopping the session's workers + the checkpoint's own
/// bounded save + 1 s margin.
const CHECKPOINT_BUDGET: Duration =
    Duration::from_secs(crate::session::budgets::RELOAD_CHECKPOINT_BUDGET_SECS);
/// What clients are told to wait before reconnecting.
pub const RETRY_AFTER_MS: u64 = 500;

#[derive(Debug, Clone, Default)]
pub struct ReloadRequest {
    pub now: bool,
    pub drain_secs: Option<u64>,
    pub exe: Option<PathBuf>,
}

impl ReloadRequest {
    pub fn from_frame(frame: &ClientFrame) -> Option<Self> {
        match frame {
            ClientFrame::Reload { now, drain_secs, exe } => {
                Some(Self { now: *now, drain_secs: *drain_secs, exe: exe.clone() })
            }
            _ => None,
        }
    }
}

#[derive(Debug)]
pub enum ReloadError {
    /// Refused before anything was disturbed (`RefuseReason::ReloadRefused`).
    Refused(String),
    /// `execv` returned: the old image continues; sessions are checkpointed.
    ExecFailed(String),
}

impl std::fmt::Display for ReloadError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Refused(w) => write!(f, "reload refused: {w}"),
            Self::ExecFailed(e) => write!(f, "reload exec failed: {e}"),
        }
    }
}

/// `<exe> daemon --print-version` output.
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct PrintVersion {
    pub binary_version: String,
    pub protocol_version: u32,
}

impl PrintVersion {
    pub fn current() -> Self {
        Self {
            binary_version: crate::session::wire::binary_version(),
            protocol_version: PROTOCOL_VERSION,
        }
    }
}

/// One recorded session.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ReloadSession {
    pub id: String,
    pub journal_id: String,
    pub config: SessionConfig,
    pub keep_warm: bool,
    pub lifecycle: SessionLifecycle,
    /// Non-persisted knobs re-`Set` after create (incl. `/system`).
    #[serde(default)]
    pub settings_replay: Vec<SessionSetting>,
    /// Per-session `/keepwarm` override (task #444), re-applied after create.
    #[serde(default)]
    pub cache_keepwarm: Option<String>,
    pub input_owner_kind: Option<crate::session::ClientKind>,
    /// Workers the checkpoint stopped (or that still owed the parent a
    /// completion wake), handed to the new image (`AdoptWorkers`).
    #[serde(default)]
    pub workers: Vec<crate::runtime::subagent::CarriedWorker>,
    /// The session's exact tool activations, restored into the new image's
    /// runtime (re-validated there; see `SessionToolSet::restore_carried`).
    /// Empty from an older image or a checkpoint that did not confirm.
    #[serde(default)]
    pub tool_activations: Vec<crate::tools::activation::CarriedActivation>,
    /// An owned session's owner token (`SessionConfig::owned` never rides
    /// the config): the next image restores it owned and unbound, waiting
    /// the re-bind grace for its owner. Never the forwarded secrets: the
    /// owner sends them again when it re-binds.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub owner_token: Option<crate::session::OwnerToken>,
}

/// `registry_dir()/daemon[-P].reload.json` body.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ReloadState {
    pub generation: u64,
    pub written_at: chrono::DateTime<chrono::Utc>,
    pub sessions: Vec<ReloadSession>,
    pub expected_clients: usize,
    /// The subagent handle counter (`sa_N`) at the exec. The new image never
    /// hands out a lower id, so a model's remembered handles keep meaning
    /// the worker they named. `0` (older reload-state): derived from the
    /// carried workers only.
    #[serde(default)]
    pub next_subagent_id: u64,
}

impl ReloadState {
    /// The first handle number the new image may use: past the old image's
    /// counter and every carried worker id.
    pub fn subagent_id_floor(&self) -> u64 {
        let carried = self
            .sessions
            .iter()
            .flat_map(|s| &s.workers)
            .filter_map(|w| crate::runtime::subagent::handle_number(&w.id))
            .max()
            .map_or(0, |n| n + 1);
        self.next_subagent_id.max(carried)
    }
}

pub fn reload_state_path(paths: &DaemonPaths) -> PathBuf {
    let stem = paths
        .json
        .file_stem()
        .map(|s| s.to_string_lossy().into_owned())
        .unwrap_or_else(|| "daemon".into());
    paths.dir.join(format!("{stem}.reload.json"))
}

/// The executable to re-exec: argv[0] canonicalised (NOT `/proc/self/exe`,
/// which reads "(deleted)" after an in-place rebuild); `current_exe` only
/// as a fallback when argv[0] is not resolvable (e.g. bare name on PATH).
pub fn resolve_exe() -> PathBuf {
    if let Some(a0) = std::env::args_os().next() {
        let p = PathBuf::from(&a0);
        if p.components().count() > 1 {
            if let Ok(c) = p.canonicalize() {
                return c;
            }
        }
    }
    std::env::current_exe().unwrap_or_else(|_| PathBuf::from("synaps"))
}

fn semver_tuple(s: &str) -> Option<(u64, u64, u64)> {
    let core = s.split(['-', '+']).next()?;
    let mut it = core.split('.').map(|p| p.parse::<u64>().ok());
    Some((it.next()??, it.next()??, it.next()??))
}

/// Directional gate (§2.1): new protocol ≥ ours (clients must still be able
/// to reconnect) and new binary ≥ ours (newer OR EQUAL; same-version
/// rebuilds are the common case).
pub fn version_gate(current: &PrintVersion, new: &PrintVersion) -> Result<(), String> {
    if new.protocol_version < current.protocol_version {
        return Err(format!(
            "new binary speaks protocol {} < {}: reconnecting clients would be refused",
            new.protocol_version, current.protocol_version
        ));
    }
    match (semver_tuple(&current.binary_version), semver_tuple(&new.binary_version)) {
        (Some(c), Some(n)) if n < c => Err(format!(
            "new binary {} is older than the running {} (reload is newer-or-equal only)",
            new.binary_version, current.binary_version
        )),
        (Some(_), Some(_)) => Ok(()),
        _ => Err(format!(
            "cannot compare versions {:?} vs {:?}",
            current.binary_version, new.binary_version
        )),
    }
}

/// M8: `--exe` must be something we would trust to `execv` in our own pid:
/// an existing regular file (canonicalised), executable, owned by our uid
/// (or root — package-installed binaries), not group/world-writable.
/// Returns the canonical path. Same-uid 0600 socket → not a privilege
/// boundary; this is a footgun guard, not a sandbox.
#[cfg(unix)]
pub fn validate_exe(exe: &Path) -> Result<PathBuf, String> {
    use std::os::unix::fs::{MetadataExt, PermissionsExt};
    let canon = exe
        .canonicalize()
        .map_err(|e| format!("--exe {}: {e}", exe.display()))?;
    let md = std::fs::metadata(&canon).map_err(|e| format!("--exe {}: {e}", canon.display()))?;
    if !md.is_file() {
        return Err(format!("--exe {}: not a regular file", canon.display()));
    }
    let mode = md.permissions().mode();
    if mode & 0o111 == 0 {
        return Err(format!("--exe {}: not executable", canon.display()));
    }
    // SAFETY: getuid has no preconditions.
    let uid = unsafe { libc::getuid() };
    if md.uid() != uid && md.uid() != 0 {
        return Err(format!(
            "--exe {}: owned by uid {} (expected {} or root)",
            canon.display(),
            md.uid(),
            uid
        ));
    }
    if mode & 0o022 != 0 {
        return Err(format!(
            "--exe {}: group/world-writable (mode {:o})",
            canon.display(),
            mode & 0o777
        ));
    }
    Ok(canon)
}

#[cfg(not(unix))]
pub fn validate_exe(exe: &Path) -> Result<PathBuf, String> {
    exe.canonicalize().map_err(|e| format!("--exe {}: {e}", exe.display()))
}

/// Run `<exe> daemon --print-version` (5 s) and parse it.
pub async fn probe_version(exe: &Path) -> Result<PrintVersion, String> {
    let out = tokio::time::timeout(
        VERSION_PROBE_TIMEOUT,
        tokio::process::Command::new(exe)
            .args(["daemon", "--print-version"])
            .env("SYNAPS_DAEMON", "1")
            .stdin(std::process::Stdio::null())
            .stderr(std::process::Stdio::piped())
            .stdout(std::process::Stdio::piped())
            .output(),
    )
    .await
    .map_err(|_| format!("{} --print-version timed out", exe.display()))?
    .map_err(|e| format!("cannot run {}: {e}", exe.display()))?;
    if !out.status.success() {
        return Err(format!(
            "{} --print-version exited {:?}: {}",
            exe.display(),
            out.status.code(),
            String::from_utf8_lossy(&out.stderr).trim()
        ));
    }
    serde_json::from_slice(&out.stdout)
        .map_err(|e| format!("{} --print-version: unparsable output ({e})", exe.display()))
}

/// `Checkpoint{Reload}` → the actor's `SessionReloadRecord` (`None` when
/// the checkpoint did not confirm in budget).
async fn checkpoint_one(handle: SessionHandle) -> Option<SessionReloadRecord> {
    let mut rx = handle.subscribe();
    if handle
        .send(SessionCommand::Checkpoint { reason: CheckpointReason::Reload })
        .await
        .is_err()
    {
        return None;
    }
    let wait = async {
        loop {
            match rx.recv().await {
                Ok(env) => {
                    if let SessionEventWire::QueryResult { id, value } = env.event {
                        if id == CHECKPOINT_QUERY_ID {
                            return serde_json::from_value(value["record"].clone()).ok();
                        }
                    }
                }
                Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => continue,
                Err(tokio::sync::broadcast::error::RecvError::Closed) => return None,
            }
        }
    };
    tokio::time::timeout(CHECKPOINT_BUDGET, wait).await.unwrap_or(None)
}

/// The session as it IS: the actor's record when the checkpoint confirmed,
/// else what the handle alone knows (journal, cwd, keep-warm, lifecycle,
/// current model from the published view, the `/keepwarm` override).
fn record(handle: &SessionHandle, rec: Option<SessionReloadRecord>) -> ReloadSession {
    let meta = handle.meta();
    let journal_id = handle.journal_id();
    if rec.is_none() {
        tracing::warn!(
            session = %handle.id,
            "reload: no checkpoint reply in time — this session's workers are not carried: \
             no archive is guaranteed and their parent will not be woken"
        );
    }
    let (config, keep_warm, lifecycle, settings_replay, cache_keepwarm, model, workers, tool_activations) = match rec {
        Some(r) => (
            r.config,
            r.keep_warm,
            r.lifecycle,
            r.settings_replay,
            r.cache_keepwarm,
            r.model,
            r.workers,
            r.tool_activations,
        ),
        None => (
            SessionConfig {
                cwd: meta.cwd.clone(),
                env: None,
            env_stripped: Vec::new(),
                ..SessionConfig::default()
            },
            // The pin is on the handle too, so it survives a reload whose
            // checkpoint did not confirm.
            handle.pinned(),
            handle.lifecycle(),
            Vec::new(),
            // Persisted independently of the checkpoint: an explicit
            // `/keepwarm` choice must survive a reload that timed out.
            handle.cache_keepwarm_override(),
            handle.view().model.clone(),
            // No checkpoint reply: whatever workers ran are lost to the exec
            // without a record (the actor never answered).
            Vec::new(),
            // Nor are its tool activations known.
            Vec::new(),
        ),
    };
    ReloadSession {
        id: meta.id.as_str().to_string(),
        journal_id: journal_id.clone(),
        config: SessionConfig {
            continue_session: Some(Some(journal_id)),
            model_override: Some(model),
            keep_warm,
            // The journal carries the CURRENT name (saveas after create);
            // re-applying the create-time `--name` would undo a rename.
            name: None,
            ..config
        },
        keep_warm,
        lifecycle,
        settings_replay,
        cache_keepwarm,
        input_owner_kind: None,
        workers,
        tool_activations,
        owner_token: handle.owner_token().cloned(),
    }
}

/// Steps 1–4 (§2.8): gate, drain, checkpoint, reload-state, announce.
/// Nothing irreversible has happened when this returns `Ok`; the caller
/// (the requesting connection) sends its own `Bye{Reloading}`, flushes,
/// then calls [`exec`].
pub struct Prepared {
    pub exe: PathBuf,
    pub rs_path: PathBuf,
    pub generation: u64,
}

pub async fn prepare(
    state: &Arc<DaemonState>,
    paths: &DaemonPaths,
    req: ReloadRequest,
) -> Result<Prepared, ReloadError> {
    // 1. version gate — before anything is disturbed.
    // The recorded exe from this image's own record (not daemon.json, which
    // can be lost while the daemon runs).
    let exe = req.exe.clone().unwrap_or_else(|| state.daemon_info().exe.unwrap_or_else(resolve_exe));
    let exe = validate_exe(&exe).map_err(ReloadError::Refused)?;
    let new = probe_version(&exe).await.map_err(ReloadError::Refused)?;
    version_gate(&PrintVersion::current(), &new).map_err(ReloadError::Refused)?;
    if state.reloading.swap(true, Ordering::SeqCst) {
        return Err(ReloadError::Refused("a reload is already in progress".into()));
    }
    let generation = state.generation + 1;
    tracing::info!(exe = %exe.display(), new = %new.binary_version, generation, "daemon: reload accepted");

    // 2. drain (refuse new work), then checkpoint every session concurrently.
    let drain = if req.now {
        Duration::ZERO
    } else {
        req.drain_secs
            .map(Duration::from_secs)
            .or_else(|| std::env::var(DRAIN_SECS_ENV).ok()?.parse().ok().map(Duration::from_secs))
            .unwrap_or(DEFAULT_DRAIN)
    };
    let t0 = std::time::Instant::now();
    while t0.elapsed() < drain {
        let mut all_idle = true;
        for h in state.live_sessions() {
            if !super::session_is_idle(&h).await {
                all_idle = false;
                break;
            }
        }
        if all_idle {
            break;
        }
        tokio::time::sleep(Duration::from_millis(200)).await;
    }
    let handles = state.live_sessions();
    let results = futures::future::join_all(handles.iter().cloned().map(checkpoint_one)).await;
    let mut sessions = Vec::with_capacity(handles.len());
    for (h, rec) in handles.iter().zip(results) {
        if rec.is_none() {
            tracing::warn!(session = %h.id, "reload: checkpoint did not confirm; recording from the handle");
        }
        sessions.push(record(h, rec));
    }

    // 3. reload-state (0600, atomic).
    let rs = ReloadState {
        generation,
        written_at: chrono::Utc::now(),
        sessions,
        expected_clients: state.connections.load(Ordering::SeqCst),
        // After every checkpoint: no session can launch a worker any more.
        next_subagent_id: crate::tools::peek_next_subagent_id(),
    };
    let rs_path = reload_state_path(paths);
    // If either write fails we early-return WITHOUT reaching exec() (which is the
    // only other place `reloading` is cleared), so reset the drain flag here —
    // otherwise a failed reload-state write bricks the daemon (it refuses every
    // new Create/Submit/Compact until restart).
    let written = serde_json::to_vec_pretty(&rs)
        .map_err(|e| e.to_string())
        .and_then(|body| registry::write_private_atomic(&rs_path, &body).map_err(|e| e.to_string()));
    if let Err(e) = written {
        // No exec will follow: every checkpointed session lifts its fence
        // and hears about the workers its checkpoint stopped.
        abort_checkpoints(state).await;
        state.reloading.store(false, Ordering::SeqCst);
        return Err(ReloadError::ExecFailed(e));
    }

    // 4. announce — every OTHER conn selects on `reload_announce` and sends
    //    Event(Reloading) + Bye{Reloading}; give their writers ≤ 1 s.
    state.reload_generation.store(generation, Ordering::SeqCst);
    state.fire_announce();
    let t1 = std::time::Instant::now();
    while state.connections.load(Ordering::SeqCst) > 1 && t1.elapsed() < Duration::from_secs(crate::session::budgets::RELOAD_ANNOUNCE_WAIT_SECS) {
        tokio::time::sleep(Duration::from_millis(20)).await;
    }
    Ok(Prepared { exe, rs_path, generation })
}

/// Step 5: rewrite `daemon.json` (generation+1, same pid), stop sidecars,
/// hand the flock to the next image and `execv`. Returns only on failure —
/// then `daemon.json`/reload-state are restored, extension discovery is
/// re-spawned (the sidecars were stopped for the exec — M4: no zombie
/// daemon without hooks), and the old image keeps serving (sessions
/// checkpointed but alive; clients that got `Bye` reconnect to THIS image
/// — a `reconnect_of.generation` mismatch is tolerated, the daemon answers
/// with its own generation).
pub async fn exec(state: &Arc<DaemonState>, p: Prepared) -> ReloadError {
    // From this image's own record, not daemon.json (which can be lost while
    // the daemon runs). The record is held and written under the metadata
    // lock, so a heal in the hand-off window writes the same.
    // `previous` stays untouched: a failed exec puts it back whole.
    let previous = state.daemon_info();
    let prev_generation = previous.generation;
    let info = registry::DaemonInfo {
        generation: p.generation,
        started_at: chrono::Utc::now(),
        exe: Some(p.exe.clone()),
        ..previous.clone()
    };
    if let Err(e) = state.meta.publish(info) {
        tracing::warn!(path = %state.paths.json.display(), error = %e, "daemon: daemon.json write failed at reload");
    }
    let _ = tokio::time::timeout(
        Duration::from_secs(crate::session::budgets::RELOAD_EXT_SHUTDOWN_SECS),
        async { state.host.ext_manager().write().await.shutdown_all().await },
    )
    .await;

    #[cfg(unix)]
    let err = exec_self(&p.exe, &p.rs_path, state);
    #[cfg(windows)]
    let err = exec_successor(&p.exe, &p.rs_path, state).await;
    tracing::error!(error = %err, "daemon: reload exec failed; continuing on the old image");
    // The record before this attempt, whole: exe and started_at too, so the
    // next default reload uses the old exe, not the one that failed.
    if let Err(e) = state.meta.publish(previous) {
        tracing::warn!(
            path = %state.paths.json.display(),
            error = %e,
            "daemon: daemon.json write failed after the failed reload exec"
        );
    }
    let _ = std::fs::remove_file(&p.rs_path);
    state.reload_generation.store(prev_generation, Ordering::SeqCst);
    state.reset_announce();
    // Sidecars were shut down for the exec: bring them back (bounded like
    // `run_foreground`'s first discovery) so the surviving image has hooks.
    let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel();
    let _loader = crate::extensions::loader::spawn_discover_and_load(
        Arc::clone(state.host.ext_manager()),
        tx,
        None,
    );
    let wait = async {
        while let Some(ev) = rx.recv().await {
            if let crate::extensions::loader::ExtensionLoaderEvent::Finished { loaded, failed } = ev {
                tracing::info!(loaded = loaded.len(), failed = failed.len(), "daemon: extensions re-discovered after failed reload");
                break;
            }
        }
    };
    if tokio::time::timeout(
        Duration::from_secs(crate::session::budgets::RELOAD_EXT_REDISCOVERY_SECS),
        wait,
    )
    .await
    .is_err()
    {
        tracing::warn!("daemon: extension re-discovery still running; resuming the sessions");
    }
    // The checkpoint fenced every session and stopped its workers for an
    // exec that did not happen: their parents are still here and still
    // waiting — lift the fences and tell them.
    abort_checkpoints(state).await;
    state.reloading.store(false, Ordering::SeqCst);
    ReloadError::ExecFailed(err)
}

#[cfg(unix)]
fn exec_self(exe: &Path, rs_path: &Path, state: &DaemonState) -> String {
    use std::os::unix::process::CommandExt;
    let Some(lock_fd) = state.lock_fd.lock().unwrap_or_else(|e| e.into_inner()).as_ref().map(|l| l.raw_fd()) else {
        return "no lock fd to inherit".into();
    };
    // Clear FD_CLOEXEC on the lock so the new image adopts the SAME flock
    // (liveness oracle never flickers). The listener keeps CLOEXEC: it is
    // closed at exec and the new image rebinds the path.
    // SAFETY: fcntl on an fd we own.
    unsafe {
        let flags = libc::fcntl(lock_fd, libc::F_GETFD);
        if flags >= 0 {
            libc::fcntl(lock_fd, libc::F_SETFD, flags & !libc::FD_CLOEXEC);
        }
    }
    let mut args: Vec<std::ffi::OsString> = std::env::args_os().skip(1).collect();
    if args.is_empty() || args.iter().all(|a| a != "daemon") {
        args = vec!["daemon".into(), "--foreground".into()];
    }
    let mut cmd = std::process::Command::new(exe);
    cmd.args(&args)
        .env("SYNAPS_DAEMON", "1")
        .env(LOCK_FD_ENV, lock_fd.to_string())
        .env(RELOAD_STATE_ENV, rs_path)
        .env(SUBAGENT_ID_FLOOR_ENV, crate::tools::peek_next_subagent_id().to_string());
    let e = cmd.exec();
    // Only reached on failure: restore CLOEXEC.
    // SAFETY: as above.
    unsafe {
        let flags = libc::fcntl(lock_fd, libc::F_GETFD);
        if flags >= 0 {
            libc::fcntl(lock_fd, libc::F_SETFD, flags | libc::FD_CLOEXEC);
        }
    }
    e.to_string()
}

/// Windows `execv`: start the new image with the reload-state and a
/// hand-off event, wait for it to queue its `daemon.lock` request behind
/// ours, then exit — no destructors (they would unlink the `daemon.json`
/// that now names the next generation), no session `End` (the new image
/// rehydrates them): what the exec discards on Unix. Returns only on
/// failure, with this image intact.
#[cfg(windows)]
async fn exec_successor(exe: &Path, rs_path: &Path, state: &DaemonState) -> String {
    use super::win;
    let armed = match win::Event::create_unique("handoff") {
        Ok(e) => e,
        Err(e) => return format!("hand-off event: {e}"),
    };
    let mut args: Vec<std::ffi::OsString> = std::env::args_os().skip(1).collect();
    if args.is_empty() || args.iter().all(|a| a != "daemon") {
        args = vec!["daemon".into(), "--foreground".into()];
    }
    let mut env = crate::process_scope::inherited_env();
    env.retain(|(k, _)| k != super::READY_EVENT_ENV);
    crate::process_scope::set_env(&mut env, "SYNAPS_DAEMON", "1");
    crate::process_scope::set_env(&mut env, RELOAD_STATE_ENV, rs_path.as_os_str());
    crate::process_scope::set_env(&mut env, HANDOFF_EVENT_ENV, armed.name());
    crate::process_scope::set_env(&mut env, HANDOFF_PID_ENV, std::process::id().to_string());
    crate::process_scope::set_env(&mut env, SUBAGENT_ID_FLOOR_ENV, crate::tools::peek_next_subagent_id().to_string());
    let child = match win::spawn_detached(exe, &args, &env) {
        Ok(c) => c,
        Err(e) => return format!("cannot start {}: {e}", exe.display()),
    };
    let waited = tokio::task::spawn_blocking(move || {
        let outcome = win::wait_event_or_exit(&armed, &child, HANDOFF_ARM_TIMEOUT);
        (child, outcome)
    })
    .await;
    let (child, outcome) = match waited {
        Ok(r) => r,
        Err(e) => return format!("hand-off wait: {e}"),
    };
    match outcome {
        win::Wait::Signalled => {
            tracing::info!(pid = child.id(), "daemon: reload hand-off armed; this image exits");
            state.host.flush_logs();
            std::process::exit(0);
        }
        win::Wait::Exited => {
            let mut child = child;
            let code = child.wait(Duration::ZERO);
            let tail = win::stderr_tail(child.take_stderr(), 64 * 1024, Duration::from_millis(500));
            let why = tail
                .lines()
                .map(str::trim)
                .rfind(|l| !l.is_empty())
                .map(|l| l.trim_start_matches("synaps daemon: ").to_string())
                .unwrap_or_else(|| "no output".into());
            format!(
                "new image exited (code {}) before taking over: {why}",
                code.map_or_else(|| "?".to_string(), |c| c.to_string())
            )
        }
        win::Wait::TimedOut => {
            child.kill();
            let _ = child.wait(Duration::from_secs(5));
            format!("new image did not take over within {HANDOFF_ARM_TIMEOUT:?}")
        }
    }
}

/// What a new image adopts: the held lock, the reload-state and its path.
type Adopted = (DaemonLock, ReloadState, PathBuf);

/// Windows: the hand-off taken at the top of `run_foreground`, held here
/// for [`adopt_from_env`].
#[cfg(windows)]
static TAKEN_OVER: std::sync::Mutex<Option<Adopted>> = std::sync::Mutex::new(None);

/// Windows: take `daemon.lock` over from the previous image now, before
/// anything boots (the previous image exits on our signal, as the exec
/// would have replaced it). A no-op unless this is a reload.
#[cfg(windows)]
pub fn take_over_from_env(paths: &DaemonPaths) -> anyhow::Result<()> {
    if let Some(adopted) = handoff_from_env(paths)? {
        *TAKEN_OVER.lock().unwrap_or_else(|e| e.into_inner()) = Some(adopted);
    }
    Ok(())
}

/// New-image side (`Daemon::start`), Windows: what [`take_over_from_env`]
/// took, or the hand-off done now.
#[cfg(windows)]
pub fn adopt_from_env(paths: &DaemonPaths) -> anyhow::Result<Option<Adopted>> {
    if let Some(adopted) = TAKEN_OVER.lock().unwrap_or_else(|e| e.into_inner()).take() {
        return Ok(Some(adopted));
    }
    handoff_from_env(paths)
}

/// Windows hand-off, new-image side: parse the reload-state first (a bad
/// one fails while the old image can still carry on), queue `daemon.lock`
/// behind the old image and set its hand-off event, take the grant when it
/// exits, then wait for its process to be gone. The event is mandatory —
/// without it the old image would never let go (refuse, as Unix refuses a
/// reload-state without its lock fd).
#[cfg(windows)]
fn handoff_from_env(paths: &DaemonPaths) -> anyhow::Result<Option<Adopted>> {
    let Some(rs_path) = std::env::var_os(RELOAD_STATE_ENV) else {
        return Ok(None);
    };
    let rs_path = PathBuf::from(rs_path);
    std::env::remove_var(RELOAD_STATE_ENV);
    let event = std::env::var(HANDOFF_EVENT_ENV).ok();
    std::env::remove_var(HANDOFF_EVENT_ENV);
    let old_pid = std::env::var(HANDOFF_PID_ENV).ok().and_then(|s| s.parse::<u32>().ok());
    std::env::remove_var(HANDOFF_PID_ENV);
    let id_floor = std::env::var(SUBAGENT_ID_FLOOR_ENV).ok().and_then(|s| s.parse::<u64>().ok());
    std::env::remove_var(SUBAGENT_ID_FLOOR_ENV);
    let event = event.ok_or_else(|| {
        anyhow::anyhow!("{RELOAD_STATE_ENV} set without {HANDOFF_EVENT_ENV}: refusing to start (the lock is the liveness oracle)")
    })?;
    let body = std::fs::read_to_string(&rs_path)?;
    let mut rs: ReloadState = serde_json::from_str(&body)?;
    if let Some(floor) = id_floor {
        rs.next_subagent_id = rs.next_subagent_id.max(floor);
    }
    // Opened before the signal, so its pid cannot be reused under us.
    let old = old_pid.and_then(super::win::Process::open);
    let mut signal_err = None;
    let lock = DaemonLock::acquire_handoff(paths, HANDOFF_EXIT_TIMEOUT, || {
        signal_err = super::win::signal_event(&event).err();
    })
    .map_err(|e| match &signal_err {
        Some(s) => anyhow::anyhow!("taking daemon.lock over: {e} (the previous image was never told: {s})"),
        None => anyhow::anyhow!("taking daemon.lock over from the previous image: {e}"),
    })?;
    if let Some(old) = old {
        if !old.wait(Duration::from_secs(10)) {
            tracing::warn!(pid = old_pid, "daemon: the previous image still runs after releasing daemon.lock");
        }
    }
    tracing::info!(generation = rs.generation, "daemon: took daemon.lock over from the previous image");
    // The previous image read our stderr; it is gone.
    super::win::detach_stdio();
    Ok(Some((lock, rs, rs_path)))
}

/// New-image side (`Daemon::start`): when `RELOAD_STATE_ENV` is set, the
/// lock is ADOPTED from `LOCK_FD_ENV` (mandatory — refuse to start without
/// it, risk §6.8) and the recorded generation is returned.
#[cfg(unix)]
pub fn adopt_from_env(_paths: &DaemonPaths) -> anyhow::Result<Option<Adopted>> {
    let Some(rs_path) = std::env::var_os(RELOAD_STATE_ENV) else {
        return Ok(None);
    };
    let rs_path = PathBuf::from(rs_path);
    std::env::remove_var(RELOAD_STATE_ENV);
    let fd: i32 = std::env::var(LOCK_FD_ENV)
        .ok()
        .and_then(|s| s.parse().ok())
        .ok_or_else(|| anyhow::anyhow!("{RELOAD_STATE_ENV} set without {LOCK_FD_ENV}: refusing to start (the flock is the liveness oracle)"))?;
    std::env::remove_var(LOCK_FD_ENV);
    let id_floor = std::env::var(SUBAGENT_ID_FLOOR_ENV).ok().and_then(|s| s.parse::<u64>().ok());
    std::env::remove_var(SUBAGENT_ID_FLOOR_ENV);
    let lock = DaemonLock::adopt(fd)?;
    let body = std::fs::read_to_string(&rs_path)?;
    let mut rs: ReloadState = serde_json::from_str(&body)?;
    if let Some(floor) = id_floor {
        rs.next_subagent_id = rs.next_subagent_id.max(floor);
    }
    Ok(Some((lock, rs, rs_path)))
}

/// Rehydrate every recorded session BEFORE accepting. A session that
/// fails to come back is logged and skipped (its journal is on disk;
/// `--continue` brings it back).
///
/// A session whose journal was never written (no turn yet — `save` skips
/// an empty conversation) cannot be continued; it is recreated fresh under
/// a new id and aliased from the old one.
/// F23: detect "is live in another process" in the error string — this is
/// the `SessionLockError::Held` case, where an in-process runtime holds
/// the journal lock. Instead of aliasing to an empty impostor, register a
/// Parked placeholder under the SAME id.
pub(crate) fn is_lock_held_error(e: &str) -> bool {
    e.contains("is live in another process")
}

/// Extract `"pid N (kind)"` from the lock-held error message.
pub(crate) fn parse_holder_from_error(e: &str) -> String {
    // "session X is live in another process (pid N, kind) — …"
    if let Some(start) = e.find("(pid ") {
        let after = &e[start + 1..]; // "pid N, kind) — …"
        if let Some(end) = after.find(')') {
            return after[..end].to_string();
        }
    }
    "unknown holder".to_string()
}

/// No exec after the checkpoints (it failed, or the reload stopped before
/// it): every live session lifts its reload fence and is handed back the
/// workers its checkpoint stopped (`ReloadAborted`, a no-op for a session
/// that never checkpointed). The actor re-announces from its own record,
/// so a checkpoint that answered too late for the reload record is covered.
async fn abort_checkpoints(state: &Arc<DaemonState>) {
    let budget = Duration::from_secs(crate::session::budgets::RELOAD_ABORT_SEND_SECS);
    let sends = state
        .live_sessions()
        .into_iter()
        .map(|h| async move { send_reload_aborted(&h, budget).await });
    futures::future::join_all(sends).await;
}

/// `ReloadAborted` must arrive: dropped, the session would wait out the
/// fence's backstop. `SessionHandle::send` never waits for queue room, so
/// retry a full queue (the actor drains it) for up to `budget`.
pub(crate) async fn send_reload_aborted(h: &SessionHandle, budget: Duration) -> bool {
    use crate::session::TransportError;
    let deadline = tokio::time::Instant::now() + budget;
    loop {
        match h.send(SessionCommand::ReloadAborted).await {
            Ok(()) => return true,
            Err(TransportError::Backpressure) if tokio::time::Instant::now() < deadline => {
                tokio::time::sleep(Duration::from_millis(20)).await;
            }
            Err(e) => {
                tracing::warn!(
                    session = %h.id,
                    error = %e,
                    "reload: could not tell the session the exec failed; its reload fence lifts at the backstop"
                );
                return false;
            }
        }
    }
}

/// The config a session is restored with: as saved, except that the
/// restore never waits on `on_session_start`. Each restored session runs
/// the hook in the background (the deferred path quick-start sessions
/// use), so the restore of N sessions does not take N hook round trips
/// while the socket waits. A session restored Parked runs it only once it
/// is unparked.
///
/// A folder that is no longer there is dropped ([`restorable_folder`]), as
/// the pinned restore drops it (`pins::restore_one`): the chat `chat` then
/// runs in the daemon's folder and its project. Kept, the dead path gave
/// the chat no project at all: discovery fails on a path it cannot resolve,
/// the memory tools answer "host project scope unavailable" and the next
/// rollover cannot seal.
fn restore_config(saved: &SessionConfig, lifecycle: SessionLifecycle, chat: &str) -> SessionConfig {
    SessionConfig {
        await_extensions: false,
        restore_parked: matches!(lifecycle, SessionLifecycle::Parked | SessionLifecycle::Parking),
        cwd: restorable_folder(saved.cwd.clone(), chat),
        ..saved.clone()
    }
}

/// The folder a chat is restored in, by a reload, as a pinned session or by
/// an unpark (`session/actor.rs`):
/// `folder` as saved, or `None` when it is gone, and the chat then runs in
/// the daemon's folder and that folder's project.
///
/// Gone means that the path does not exist, is not a directory, or runs
/// through something that is not a directory (a file where one of its
/// parents was), which no folder can be under. A folder that cannot be
/// looked at for a reason that can pass (no permission, a mount that is
/// away for a moment, an I/O error) is kept: the chat stays in its
/// own project, where its tools fail until the folder is back, rather than
/// being moved to another project's files and memory without a word. Every
/// drop is logged with the folder and the chat. The lines name no host: an
/// unpark in a host that is not the daemon writes them too.
pub(crate) fn restorable_folder(folder: Option<PathBuf>, chat: &str) -> Option<PathBuf> {
    let folder = folder?;
    let gone = match std::fs::metadata(&folder) {
        Ok(found) if found.is_dir() => return Some(folder),
        Ok(_) => "it is not a directory",
        Err(error) if error.kind() == std::io::ErrorKind::NotFound => "it does not exist",
        Err(error) if error.kind() == std::io::ErrorKind::NotADirectory => {
            "its path runs through something that is not a directory"
        }
        Err(error) => {
            tracing::warn!(
                session = %chat,
                folder = %folder.display(),
                error = %error,
                "{}",
                UNSEEN_NOTICE
            );
            return Some(folder);
        }
    };
    tracing::warn!(
        session = %chat,
        folder = %folder.display(),
        "{}",
        gone_notice(gone)
    );
    None
}

/// What [`restorable_folder`] logs for a folder it keeps without having
/// seen it. Like [`gone_notice`] it names no host.
const UNSEEN_NOTICE: &str = "the chat's folder cannot be looked at; restored with it all the same";

/// What [`restorable_folder`] logs for a folder it drops, `gone` being why.
/// It names no host ("daemon:" it once began with): a reload and a pinned
/// restore run in the daemon, an unpark in whichever host holds the chat.
fn gone_notice(gone: &str) -> String {
    format!(
        "the chat's folder is gone ({gone}); it is restored in the host process's folder \
         and that folder's project"
    )
}

pub async fn rehydrate(state: &Arc<DaemonState>, rs: &ReloadState) {
    // Before any session can dispatch: ids continue where the old image
    // stopped, so `sa_1` never names two different workers.
    crate::tools::seed_next_subagent_id(rs.subagent_id_floor());
    for s in &rs.sessions {
        // Owned: restored unbound, its grace armed only once this image
        // accepts connections (`Daemon::start`), its autonomous work held
        // until the owner re-binds.
        let owned = s.owner_token.clone().map(|token| crate::session::OwnedConfig { token, restored: true });
        let config = SessionConfig { owned, ..restore_config(&s.config, s.lifecycle, &s.id) };
        let created = match state.create(config.clone()).await {
            Ok(h) => Ok(h),
            // F23: journal locked by another process — register a Parked
            // placeholder under the SAME id. No alias, no fresh session.
            Err(e) if is_lock_held_error(&e) => {
                let holder = parse_holder_from_error(&e);
                tracing::warn!(
                    session = %s.id, holder = %holder,
                    "daemon: journal locked by another process; registering Parked placeholder"
                );
                let sid = crate::session::SessionId::from(s.id.as_str());
                // `config`, not `s.config`: an owned session stays owned.
                let (handle, _task) = crate::session::handle::locked_placeholder::spawn(
                    sid,
                    config.clone(),
                    holder,
                );
                state.insert(handle);
                continue;
            }
            Err(e) if s.config.continue_session.is_some() => {
                tracing::warn!(session = %s.id, error = %e, "daemon: journal not continuable; recreating fresh");
                state
                    .create(SessionConfig {
                        continue_session: None,
                        ..config.clone()
                    })
                    .await
            }
            Err(e) => Err(e),
        };
        match created {
            Ok(h) => {
                let new_id = h.id.as_str().to_string();
                // First, before anything can start a turn: the same
                // conversation continues in this image, so the grants it
                // held come with it (re-validated by the new runtime at its
                // first turn start). A session recreated fresh (journal not
                // continuable) is a new conversation and inherits none.
                let continued = h.meta().continued;
                if continued && !s.tool_activations.is_empty() {
                    let _ = h
                        .send(SessionCommand::RestoreToolActivations {
                            activations: s.tool_activations.clone(),
                        })
                        .await;
                }
                if new_id != s.id {
                    state
                        .reload_aliases
                        .lock()
                        .unwrap_or_else(|e| e.into_inner())
                        .insert(s.id.clone(), new_id.clone());
                }
                // Non-persisted knobs (host-originated `Set`: no owner check).
                for (i, setting) in s.settings_replay.iter().enumerate() {
                    let _ = h
                        .send(SessionCommand::Set {
                            id: u64::MAX - i as u64,
                            setting: setting.clone(),
                        })
                        .await;
                }
                if s.keep_warm {
                    let _ = h.send(SessionCommand::KeepWarm { on: true }).await;
                }
                if let Some(mode) = &s.cache_keepwarm {
                    let _ = h
                        .send(SessionCommand::EngineCommand {
                            id: u64::MAX,
                            name: "keepwarm".into(),
                            arg: mode.clone(),
                        })
                        .await;
                }
                // Before any Park: re-register the stopped workers and wake
                // their parent (it was waiting on completions the exec ate).
                if !s.workers.is_empty() {
                    let _ = h
                        .send(SessionCommand::AdoptWorkers { workers: s.workers.clone() })
                        .await;
                }
                if matches!(s.lifecycle, SessionLifecycle::Parked | SessionLifecycle::Parking) {
                    let _ = h.send(SessionCommand::Park).await;
                } else {
                    // Last, after the pin, keep-warm and workers it weighs:
                    // the old image's park timer died with the exec, and a
                    // session nobody reconnects to gets no detach to arm one.
                    let _ = h.send(SessionCommand::ArmPark).await;
                }
                tracing::info!(old = %s.id, new = %new_id, lifecycle = ?s.lifecycle, "daemon: session rehydrated after reload");
            }
            Err(e) => tracing::warn!(session = %s.id, error = %e, "daemon: session could not be rehydrated"),
        }
    }
}

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

    /// The session's tool activations ride the reload-state file; a file
    /// from an older image (no field) reads as none.
    #[test]
    fn reload_session_carries_tool_activations() {
        use crate::tools::activation::{CarriedActivation, CarriedProvenance};
        let carried = vec![CarriedActivation {
            tool_id: "builtin:subagent_start".into(),
            schema_digest: "cd".repeat(32),
            provenance: CarriedProvenance::BuiltinRuntime,
        }];
        let s = ReloadSession {
            id: "s".into(),
            journal_id: "j".into(),
            config: SessionConfig::default(),
            keep_warm: false,
            lifecycle: SessionLifecycle::Live,
            settings_replay: Vec::new(),
            cache_keepwarm: None,
            input_owner_kind: None,
            workers: Vec::new(),
            tool_activations: carried.clone(),
            owner_token: None,
        };
        let v = serde_json::to_value(&s).unwrap();
        let back: ReloadSession = serde_json::from_value(v.clone()).unwrap();
        assert_eq!(back.tool_activations, carried);
        // Never via the create config's wire form.
        assert!(v["config"].get("restore_tool_activations").is_none());

        let mut older = v;
        older.as_object_mut().unwrap().remove("tool_activations");
        let back: ReloadSession = serde_json::from_value(older).unwrap();
        assert!(back.tool_activations.is_empty());
    }

    /// Reload-state written by an older image (no workers, no counter)
    /// still parses: the new fields default.
    #[test]
    fn reload_state_from_an_older_image_parses() {
        let rs: ReloadState = serde_json::from_value(serde_json::json!({
            "generation": 9,
            "written_at": "2026-10-14T18:17:03Z",
            "sessions": [],
            "expected_clients": 1
        }))
        .unwrap();
        assert_eq!(rs.next_subagent_id, 0);
        assert_eq!(rs.subagent_id_floor(), 0);
    }

    /// The new image's first handle is past the old counter AND past every
    /// carried id (an older writer that only carried workers still works).
    #[test]
    fn subagent_id_floor_covers_the_counter_and_every_carried_id() {
        let worker = |id: &str| crate::runtime::subagent::CarriedWorker {
            id: id.into(),
            subagent_id: 0,
            agent: String::new(),
            status: "cancelled".into(),
            archive_path: None,
            stopped_by_reload: true,
            wake_lost: false,
            wake: true,
            elapsed_secs: 0,
            preview: String::new(),
        };
        let session = |workers| ReloadSession {
            id: "s".into(),
            journal_id: "j".into(),
            config: SessionConfig::default(),
            keep_warm: false,
            lifecycle: SessionLifecycle::Live,
            settings_replay: Vec::new(),
            cache_keepwarm: None,
            input_owner_kind: None,
            workers,
            tool_activations: Vec::new(),
            owner_token: None,
        };
        let mut rs = ReloadState {
            generation: 10,
            written_at: chrono::Utc::now(),
            sessions: vec![session(vec![worker("sa_288"), worker("sa_286")]), session(vec![])],
            expected_clients: 0,
            next_subagent_id: 0,
        };
        assert_eq!(rs.subagent_id_floor(), 289);
        rs.next_subagent_id = 300;
        assert_eq!(rs.subagent_id_floor(), 300);
        // Round trip keeps both.
        let back: ReloadState = serde_json::from_slice(&serde_json::to_vec(&rs).unwrap()).unwrap();
        assert_eq!(back.subagent_id_floor(), 300);
        assert_eq!(back.sessions[0].workers.len(), 2);
    }

    fn pv(b: &str, p: u32) -> PrintVersion {
        PrintVersion { binary_version: b.into(), protocol_version: p }
    }

    #[test]
    fn gate_is_directional_newer_or_equal() {
        let cur = pv("0.9.0", 2);
        assert!(version_gate(&cur, &pv("0.9.0", 2)).is_ok(), "equal allowed");
        assert!(version_gate(&cur, &pv("0.9.1", 2)).is_ok());
        assert!(version_gate(&cur, &pv("1.0.0-rc1", 3)).is_ok());
        assert!(version_gate(&cur, &pv("0.8.9", 2)).is_err(), "older refused");
        assert!(version_gate(&cur, &pv("0.9.0", 1)).is_err(), "older protocol refused");
        assert!(version_gate(&cur, &pv("garbage", 2)).is_err());
        // Two-digit minor (daemon dev builds report 0.9.1 → 0.10.0): compared
        // numerically, not as strings — "10" < "9" lexically would refuse it.
        assert!(
            version_gate(&pv("0.9.1", 3), &pv("0.10.0", 3)).is_ok(),
            "0.10.0 is newer than 0.9.1"
        );
        assert!(
            version_gate(&pv("0.10.0", 3), &pv("0.9.1", 3)).is_err(),
            "0.9.1 is older than 0.10.0"
        );
    }

    #[cfg(unix)]
    #[test]
    fn validate_exe_refuses_missing_dirs_non_exec_and_writable() {
        use std::os::unix::fs::PermissionsExt;
        let d = tempfile::tempdir().unwrap();
        assert!(validate_exe(&d.path().join("nope")).unwrap_err().contains("nope"));
        assert!(validate_exe(d.path()).unwrap_err().contains("not a regular file"));
        let f = d.path().join("bin");
        std::fs::write(&f, "#!/bin/sh\nexit 0\n").unwrap();
        std::fs::set_permissions(&f, std::fs::Permissions::from_mode(0o644)).unwrap();
        assert!(validate_exe(&f).unwrap_err().contains("not executable"));
        std::fs::set_permissions(&f, std::fs::Permissions::from_mode(0o777)).unwrap();
        assert!(validate_exe(&f).unwrap_err().contains("writable"));
        std::fs::set_permissions(&f, std::fs::Permissions::from_mode(0o755)).unwrap();
        assert_eq!(validate_exe(&f).unwrap(), f.canonicalize().unwrap());
        // A symlink resolves to its target.
        let l = d.path().join("link");
        std::os::unix::fs::symlink(&f, &l).unwrap();
        assert_eq!(validate_exe(&l).unwrap(), f.canonicalize().unwrap());
    }

    /// A restored session never waits on `on_session_start` at create; the
    /// rest of its saved config is kept. One restored Parked defers the hook
    /// to its unpark, and that flag never goes on the wire.
    #[test]
    fn a_restore_does_not_wait_on_the_session_start_hook() {
        let saved = SessionConfig {
            model_override: Some("claude-sonnet-4-5".into()),
            keep_warm: true,
            await_extensions: true,
            ..Default::default()
        };
        let restored = restore_config(&saved, SessionLifecycle::Live, "chat");
        assert!(!restored.await_extensions);
        assert!(!restored.restore_parked);
        let as_saved = SessionConfig {
            await_extensions: true,
            ..restored
        };
        assert_eq!(
            serde_json::to_value(&as_saved).unwrap(),
            serde_json::to_value(&saved).unwrap()
        );
        for parked in [SessionLifecycle::Parked, SessionLifecycle::Parking] {
            let restored = restore_config(&saved, parked, "chat");
            assert!(restored.restore_parked, "{parked:?}");
            assert!(!restored.await_extensions);
            let wire = serde_json::to_value(&restored).unwrap();
            assert!(wire.get("restore_parked").is_none(), "never on the wire");
        }
    }

    /// A chat whose folder was deleted while the daemon held it. The pinned
    /// restore drops such a folder (`pins::restore_one`, by the same
    /// [`restorable_folder`]) and the chat runs in the
    /// daemon's folder: a runtime without a folder of its own takes the
    /// process's. A reload kept the dead path. The chat's memory binding was
    /// then built on a path project discovery cannot resolve, so it had no
    /// project: memory tools answered "host project scope unavailable" and a
    /// rollover could not seal. Reload now drops it too.
    #[test]
    fn a_restore_drops_a_folder_that_is_gone_as_the_pinned_restore_does() {
        let parent = tempfile::tempdir().unwrap();
        let (kept, gone) = (parent.path().join("kept"), parent.path().join("gone"));
        std::fs::create_dir(&kept).unwrap();
        let saved = |folder: &Path| SessionConfig {
            cwd: Some(folder.to_path_buf()),
            ..Default::default()
        };

        // What the dead path does to a chat that keeps it.
        let binding = crate::memory_backend::MemoryBinding::for_cwd(Some(gone.clone()));
        let error = binding.scope().unwrap_err().to_string();
        assert!(error.contains("host project scope unavailable"), "{error}");
        let binding = crate::memory_backend::MemoryBinding::for_cwd(Some(kept.clone()));
        assert!(binding.scope().is_ok());

        for lifecycle in [SessionLifecycle::Live, SessionLifecycle::Parked] {
            assert_eq!(restore_config(&saved(&kept), lifecycle, "chat").cwd, Some(kept.clone()));
            assert_eq!(restore_config(&saved(&gone), lifecycle, "chat").cwd, None, "{lifecycle:?}");
        }
        // A file where the folder was is not a folder to run in either.
        std::fs::write(&gone, b"").unwrap();
        assert_eq!(restore_config(&saved(&gone), SessionLifecycle::Live, "chat").cwd, None);
        // No folder saved: nothing to drop.
        assert_eq!(restore_config(&SessionConfig::default(), SessionLifecycle::Live, "chat").cwd, None);
    }

    /// The two lines `restorable_folder` logs do not say "daemon": an unpark
    /// in a host that is not the daemon goes through the same function.
    /// (The text is checked, not a captured log: a log captured on one test
    /// thread loses lines to tracing's callsite cache when another test
    /// reaches the same line first.)
    #[test]
    fn the_lines_about_a_chats_folder_name_no_host() {
        let gone = gone_notice("it does not exist");
        assert!(gone.starts_with("the chat's folder is gone (it does not exist); "), "{gone}");
        for line in [gone.as_str(), UNSEEN_NOTICE] {
            assert!(line.starts_with("the chat's folder "), "{line}");
            assert!(!line.contains("daemon"), "{line}");
        }
    }

    /// The rule a reload and the pinned restore share. A folder is dropped,
    /// and the chat moved to the daemon's folder and project, only when it
    /// is known to be gone. `is_dir()` said "gone" for every failure, so a
    /// folder that could not be looked at for a moment (a mount that was
    /// away, a permission) moved the chat as well, without a log line.
    #[cfg(unix)]
    #[test]
    fn a_folder_is_dropped_only_when_it_is_absent_or_not_a_directory() {
        use std::os::unix::fs::PermissionsExt;
        let parent = tempfile::tempdir().unwrap();
        let at = |name: &str| parent.path().join(name);
        let restored = |folder: &Path| restorable_folder(Some(folder.to_path_buf()), "chat");
        assert_eq!(restorable_folder(None, "chat"), None);

        // Absent, and a file: dropped.
        assert_eq!(restored(&at("absent")), None);
        std::fs::write(at("file"), b"").unwrap();
        assert_eq!(restored(&at("file")), None);
        // A path under a file (ENOTDIR, not ENOENT): no folder can be
        // there, so it is absent, whatever is asked for under it.
        let under = at("file").join("project");
        let not_a_directory = std::fs::metadata(&under).unwrap_err().kind();
        assert_eq!(not_a_directory, std::io::ErrorKind::NotADirectory);
        assert_eq!(restored(&under), None);
        assert_eq!(restored(&under.join("deeper")), None);
        // A link to nothing is absent too.
        std::os::unix::fs::symlink(at("absent"), at("dangling")).unwrap();
        assert_eq!(restored(&at("dangling")), None);

        // A directory, and a link to one: kept, as saved.
        std::fs::create_dir(at("dir")).unwrap();
        assert_eq!(restored(&at("dir")), Some(at("dir")));
        std::os::unix::fs::symlink(at("dir"), at("link")).unwrap();
        assert_eq!(restored(&at("link")), Some(at("link")));

        // A folder that is there and cannot be looked at: kept. The same
        // answer whether or not it exists behind the closed directory, which
        // is the point: nobody can tell from here.
        let closed = at("closed");
        std::fs::create_dir_all(closed.join("project")).unwrap();
        let mode = |mode: u32| {
            std::fs::set_permissions(&closed, std::fs::Permissions::from_mode(mode)).unwrap()
        };
        mode(0o000);
        let denied = |path: &Path| {
            std::fs::metadata(path).is_err_and(|e| e.kind() == std::io::ErrorKind::PermissionDenied)
        };
        // Root reads through any mode: nothing to test there.
        if denied(&closed.join("project")) {
            assert!(!closed.join("project").is_dir(), "what the old rule went by");
            for hidden in [closed.join("project"), closed.join("nothing")] {
                assert_eq!(restored(&hidden), Some(hidden.clone()));
            }
        }
        mode(0o700);
        assert_eq!(restored(&closed.join("project")), Some(closed.join("project")));
        assert_eq!(restored(&closed.join("nothing")), None);
    }

    #[test]
    fn reload_state_path_follows_profile() {
        let d = tempfile::tempdir().unwrap();
        let p = registry::daemon_paths_in(d.path(), Some("work"));
        assert!(reload_state_path(&p).ends_with("daemon-work.reload.json"), "{:?}", reload_state_path(&p));
        let p = registry::daemon_paths_in(d.path(), None);
        assert!(reload_state_path(&p).ends_with("daemon.reload.json"));
    }

    /// Task #444: a reload whose checkpoint did not confirm (`rec == None`)
    /// still carries the explicit `/keepwarm` choice, read from the handle,
    /// instead of resurrecting the config default.
    #[test]
    fn keepwarm_override_survives_an_unconfirmed_checkpoint() {
        use crate::core::config::CacheKeepWarm;
        use crate::session::handle::echo::{meta_for, view_for};
        let id = crate::session::SessionId("kw-reload".into());
        let (handle, ep) = SessionHandle::new(meta_for(&id), view_for());
        assert_eq!(record(&handle, None).cache_keepwarm, None, "no override yet");
        // What the actor writes on `/keepwarm off`.
        *ep.cache_keepwarm.lock().unwrap() = Some(CacheKeepWarm::Off);
        assert_eq!(record(&handle, None).cache_keepwarm.as_deref(), Some("off"));
        *ep.cache_keepwarm.lock().unwrap() = Some(CacheKeepWarm::Hours(6));
        assert_eq!(record(&handle, None).cache_keepwarm.as_deref(), Some("6h"));
    }

    /// Likewise the pin: an unconfirmed checkpoint must not unpin a
    /// session (it would park, and stop holding the daemon's idle exit).
    #[test]
    fn the_pin_survives_an_unconfirmed_checkpoint() {
        use crate::session::handle::echo::{meta_for, view_for};
        let id = crate::session::SessionId("pin-reload".into());
        let (handle, ep) = SessionHandle::new(meta_for(&id), view_for());
        assert!(!record(&handle, None).keep_warm);
        ep.keep_warm.store(true, std::sync::atomic::Ordering::Release);
        let r = record(&handle, None);
        assert!(r.keep_warm && r.config.keep_warm);
    }

    /// T-B4: a session config written before the session memory mode was
    /// removed still carries `memory_mode`. It is read and ignored, in the
    /// config alone and inside a reload state, whatever its value, and the
    /// rest of the config is kept.
    #[test]
    fn an_old_memory_mode_is_read_and_ignored() {
        for v in [
            serde_json::json!("capture_and_recall"),
            serde_json::json!("off"),
            serde_json::json!("recall_forever"),
            serde_json::json!(7),
            serde_json::Value::Null,
        ] {
            let cfg: SessionConfig = serde_json::from_value(serde_json::json!({
                "memory_mode": v,
                "model_override": "claude-sonnet-4-5",
                "keep_warm": true
            }))
            .unwrap_or_else(|e| panic!("memory_mode = {v}: {e}"));
            assert_eq!(cfg.model_override.as_deref(), Some("claude-sonnet-4-5"));
            assert!(cfg.keep_warm);
            let back = serde_json::to_value(&cfg).unwrap();
            assert!(back.get("memory_mode").is_none(), "not written back: {back}");
        }
        let rs: ReloadState = serde_json::from_value(serde_json::json!({
            "generation": 2,
            "written_at": "2026-10-14T18:17:03Z",
            "sessions": [{
                "id": "s1", "journal_id": "s1", "keep_warm": false, "lifecycle": "live",
                "config": { "memory_mode": "capture_and_recall", "cwd": "/srv/chat" }
            }],
            "expected_clients": 0
        }))
        .expect("the reload state still parses");
        assert_eq!(rs.sessions.len(), 1);
        let restored = restore_config(&rs.sessions[0].config, SessionLifecycle::Live, "s1");
        assert!(!restored.await_extensions);
    }

    /// The restore without the hook wait, Parked or not.
    #[test]
    fn a_restore_keeps_the_sessions_memory_choice() {
        let saved = SessionConfig {
            await_extensions: true,
            ..Default::default()
        };
        for lifecycle in [SessionLifecycle::Live, SessionLifecycle::Parked, SessionLifecycle::Parking] {
            let restored = restore_config(&saved, lifecycle, "chat");
            assert!(!restored.await_extensions, "{lifecycle:?}");
        }
    }

    /// `ReloadAborted` reaches a session whose command queue is full (the
    /// actor drains it) instead of being dropped, which would leave the
    /// session fenced until the backstop.
    #[tokio::test]
    async fn reload_aborted_waits_for_room_in_a_full_queue() {
        use crate::session::handle::echo::{meta_for, view_for};
        let id = crate::session::SessionId("abort-full".into());
        let (handle, mut ep) = SessionHandle::new(meta_for(&id), view_for());
        while handle.send(SessionCommand::Save).await.is_ok() {}
        let drain = tokio::spawn(async move {
            tokio::time::sleep(Duration::from_millis(100)).await;
            let mut got_abort = false;
            while let Some(a) = ep.cmd_rx.recv().await {
                if matches!(a.cmd, SessionCommand::ReloadAborted) {
                    got_abort = true;
                    break;
                }
            }
            got_abort
        });
        assert!(send_reload_aborted(&handle, Duration::from_secs(5)).await);
        assert!(drain.await.unwrap(), "delivered");
        // No room ever: gives up within its budget, reporting it.
        let id = crate::session::SessionId("abort-stuck".into());
        let (stuck, _ep) = SessionHandle::new(meta_for(&id), view_for());
        while stuck.send(SessionCommand::Save).await.is_ok() {}
        assert!(!send_reload_aborted(&stuck, Duration::from_millis(100)).await);
    }
}