//! Minimal privileged helper for hive-c0re.
//!
//! Runs as root. Exposes a narrow unix socket at `/run/hive/priv.sock`
//! that accepts `PrivRequest` JSON lines and executes only the
//! operations that genuinely require root. All coordination logic,
//! broker, HTTP, and scheduling stay in the unprivileged hive-c0re
//! process.
//!
//! **Security model**: every request is validated against a strict
//! container-name allowlist before any filesystem or process operation.
//! Only containers whose names match the hive convention (`h-*`,
//! the manager container, or known sibling service containers) are
//! accepted. Every variant maps to a single known operation — no
//! arbitrary command pass-through.
//!
//! **Socket activation**: when systemd passes the listener socket via
//! `LISTEN_FDS=1` + `LISTEN_PID=<self>`, the inherited fd 3 is used
//! instead of binding a fresh socket.

use std::os::fd::{AsRawFd as _, FromRawFd as _, OwnedFd, RawFd};
use std::path::{Path, PathBuf};

use anyhow::{Context as _, Result, bail};
use hive_priv_sock::{
    AGENT_PREFIX, AGENT_RUNTIME_ROOT, AGENT_STATE_ROOT, AgentTmpfilesEntry, BindMount,
    CredentialMount, InfraAction, InfraContainer, JournalQuery, META_DIR, MIGRATE_STAGING_ROOT,
    NetworkIsolation, PAUSED_MARKER_FILE, PRIV_SOCK, PrivEvent, PrivRequest, PrivResponse,
    PrivStream, PrivStreamLine, SIBLING_CONTAINERS,
};
use serde::Serialize;
use tokio::io::{AsyncWriteExt, BufReader};
use tokio::net::unix::OwnedWriteHalf;
use tokio::net::{UnixListener, UnixStream};
use tokio::process::Command;

/// Root of the per-agent unix-socket dirs on the host.
const SOCKET_DIR_ROOT: &str = "/run/hive-agent";

#[tokio::main]
async fn main() -> Result<()> {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()),
        )
        .init();

    let listener = socket_listener()?;
    tracing::info!("hive-priv listening");

    loop {
        match listener.accept().await {
            Ok((stream, _)) => {
                tokio::spawn(handle(stream));
            }
            Err(e) => {
                tracing::error!(error = %e, "accept failed");
            }
        }
    }
}

fn socket_listener() -> Result<UnixListener> {
    // hive-priv is ALWAYS socket-activated by the `hive-priv.socket` unit
    // (fd 3 via LISTEN_FDS). There is intentionally no self-bind fallback,
    // so dev and prod take the same path; see docs/boundary.md.
    let listen_fds: Option<i32> = std::env::var("LISTEN_FDS")
        .ok()
        .and_then(|s| s.parse().ok());
    let listen_pid: Option<u32> = std::env::var("LISTEN_PID")
        .ok()
        .and_then(|s| s.parse().ok());

    let activated =
        matches!(listen_fds, Some(n) if n >= 1) && listen_pid == Some(std::process::id());
    if !activated {
        bail!(
            "hive-priv requires systemd socket activation (expected LISTEN_FDS>=1 + \
             LISTEN_PID=<self> for {PRIV_SOCK}); run it via the hive-priv.socket unit, \
             not directly"
        );
    }

    // SAFETY: systemd has passed us a ready UnixListener on fd 3.
    let std_listener = unsafe {
        use std::os::unix::io::FromRawFd;
        std::os::unix::net::UnixListener::from_raw_fd(3)
    };
    std_listener
        .set_nonblocking(true)
        .context("set socket non-blocking")?;
    let listener =
        tokio::net::UnixListener::from_std(std_listener).context("wrap systemd socket")?;
    tracing::info!("using systemd-activated socket");
    Ok(listener)
}

/// Ancillary-data buffer sized and aligned for one `SCM_RIGHTS` message.
///
/// `CMSG_SPACE` is not a `const fn`, so the size is a literal with room
/// to spare (24 bytes are needed for a single descriptor on x86-64). The
/// union member gives the `cmsghdr` alignment `CMSG_FIRSTHDR` requires —
/// a bare `[u8; N]` is only byte-aligned and would be undefined behaviour
/// to walk.
#[repr(C)]
union CmsgSpace {
    _align: libc::cmsghdr,
    bytes: [u8; 32],
}

/// One `recvmsg` into `buf`, returning the bytes read plus any file
/// descriptors that rode along as `SCM_RIGHTS`.
///
/// Why not a plain read: ancillary data is attached to a *specific*
/// `recvmsg` call, so a buffered line reader cannot surface it — it
/// reads the bytes and silently drops the descriptor.
///
/// `MSG_CMSG_CLOEXEC` is not optional: without it a received descriptor
/// is inherited by every `btrfs` / `nixos-container` child this helper
/// later spawns.
fn recv_with_fds(sock: RawFd, buf: &mut [u8]) -> std::io::Result<(usize, Vec<OwnedFd>)> {
    const FD_SIZE: usize = std::mem::size_of::<RawFd>();

    let mut iov = libc::iovec {
        iov_base: buf.as_mut_ptr().cast(),
        iov_len: buf.len(),
    };
    let mut cmsg = CmsgSpace { bytes: [0; 32] };
    // SAFETY: msghdr is a plain C struct with no invalid bit patterns;
    // every field we care about is set immediately below.
    let mut msg: libc::msghdr = unsafe { std::mem::zeroed() };
    msg.msg_iov = &raw mut iov;
    msg.msg_iovlen = 1;
    msg.msg_control = std::ptr::addr_of_mut!(cmsg.bytes).cast();
    msg.msg_controllen = 32;

    // SAFETY: `msg` points at a live iovec covering `buf` and a live,
    // correctly aligned control buffer of the length we just declared.
    let n = unsafe { libc::recvmsg(sock, &raw mut msg, libc::MSG_CMSG_CLOEXEC) };
    if n < 0 {
        return Err(std::io::Error::last_os_error());
    }

    // Take ownership of every descriptor the kernel attached, even ones
    // this protocol never expects: an `OwnedFd` we drop is closed, an
    // fd we fail to claim is leaked for the lifetime of the process.
    let mut fds = Vec::new();
    // SAFETY: `msg` was just filled in by a successful `recvmsg`.
    let mut cmsgp = unsafe { libc::CMSG_FIRSTHDR(&raw const msg) };
    while !cmsgp.is_null() {
        // SAFETY: CMSG_FIRSTHDR / CMSG_NXTHDR only ever return a pointer
        // to a complete header inside the control buffer.
        let hdr = unsafe { std::ptr::read_unaligned(cmsgp) };
        if hdr.cmsg_level == libc::SOL_SOCKET && hdr.cmsg_type == libc::SCM_RIGHTS {
            // SAFETY: same, and CMSG_LEN(0) is the header's own length.
            let payload = hdr.cmsg_len as usize - unsafe { libc::CMSG_LEN(0) } as usize;
            let count = payload / FD_SIZE;
            // SAFETY: CMSG_DATA points at `payload` bytes of descriptors.
            let data = unsafe { libc::CMSG_DATA(cmsgp) };
            for i in 0..count {
                // Copied out byte-wise rather than read through a
                // `*const RawFd`: the control buffer is only guaranteed
                // `cmsghdr`-aligned, so casting to a more strictly
                // aligned pointer would be unsound even where it happens
                // to work.
                let mut raw = [0u8; FD_SIZE];
                // SAFETY: i < count, so this reads inside the payload.
                unsafe {
                    std::ptr::copy_nonoverlapping(data.add(i * FD_SIZE), raw.as_mut_ptr(), FD_SIZE);
                }
                // SAFETY: the kernel just created this descriptor for
                // us — we are its only owner.
                fds.push(unsafe { OwnedFd::from_raw_fd(RawFd::from_ne_bytes(raw)) });
            }
        }
        // SAFETY: `cmsgp` came from this same message.
        cmsgp = unsafe { libc::CMSG_NXTHDR(&raw const msg, cmsgp) };
    }

    // `n >= 0` was checked above, so the conversion cannot fail; going
    // through `try_from` keeps it a cast-free, lint-clean widening.
    let read = usize::try_from(n).unwrap_or_default();
    Ok((read, fds))
}

/// Reads newline-delimited requests off one connection, pairing each
/// with the descriptor that arrived with it.
///
/// The pairing is deliberately trivial, because the protocol is:
/// `hive-sock-client` connects per request, so a connection carries one
/// line and at most one descriptor. The loop below still handles several
/// sequential requests (the server always has), but it refuses to guess
/// — a second descriptor arriving before its line is a protocol error,
/// not something to queue and hope about.
struct Requests<'a> {
    sock: &'a UnixStream,
    buf: Vec<u8>,
    fd: Option<OwnedFd>,
}

impl Requests<'_> {
    /// Next complete request line and its descriptor, or `None` at EOF.
    async fn next(&mut self) -> Result<Option<(String, Option<OwnedFd>)>> {
        loop {
            if let Some(nl) = self.buf.iter().position(|&b| b == b'\n') {
                let line: Vec<u8> = self.buf.drain(..=nl).take(nl).collect();
                let line = String::from_utf8(line).context("request line was not valid UTF-8")?;
                return Ok(Some((line, self.fd.take())));
            }

            let mut chunk = [0u8; 8192];
            let raw = self.sock.as_raw_fd();
            let (n, fds) = self
                .sock
                .async_io(tokio::io::Interest::READABLE, || {
                    recv_with_fds(raw, &mut chunk)
                })
                .await
                .context("recvmsg on the priv socket")?;

            for fd in fds {
                if self.fd.replace(fd).is_some() {
                    bail!("more than one file descriptor passed for a single request");
                }
            }
            if n == 0 {
                if !self.buf.is_empty() {
                    bail!("connection closed mid-request ({} bytes)", self.buf.len());
                }
                return Ok(None);
            }
            self.buf.extend_from_slice(&chunk[..n]);
        }
    }
}

async fn handle(stream: UnixStream) {
    let (reader, mut writer) = stream.into_split();
    let mut requests = Requests {
        sock: reader.as_ref(),
        buf: Vec::new(),
        fd: None,
    };
    loop {
        let (line, fd) = match requests.next().await {
            Ok(Some(req)) => req,
            Ok(None) => break,
            Err(e) => {
                tracing::warn!(error = %format!("{e:#}"), "reading request failed");
                break;
            }
        };
        let resp = dispatch(&line, fd, &mut writer).await;
        // Write the terminal PrivResponse as a PrivEvent::Done. Wire-identical
        // to a bare PrivResponse (untagged), so old hive-c0re callers that
        // deserialise directly to PrivResponse continue to work.
        let event = PrivEvent::Done(resp);
        let mut json = serde_json::to_string(&event).unwrap_or_else(|e| {
            format!("{{\"ok\":false,\"stdout\":\"\",\"stderr\":\"\",\"error\":\"serialise failed: {e}\"}}")
        });
        json.push('\n');
        if let Err(e) = writer.write_all(json.as_bytes()).await {
            tracing::warn!(error = %e, "write response failed");
            break;
        }
    }
}

/// Reject a request whose descriptor and operation disagree, in either
/// direction.
///
/// No guessing when the caller didn't say: an op that streams into a
/// passed descriptor cannot invent one, and an op that takes none must
/// not silently accept one. Returning the `Err` here drops the
/// `OwnedFd`, which closes it.
fn check_fd_agreement(req: &PrivRequest, fd: Option<&OwnedFd>) -> Result<()> {
    let wants_fd = matches!(req, PrivRequest::SendAgentSnapshotToFd { .. });
    match (wants_fd, fd.is_some()) {
        (true, false) => bail!("this operation requires a passed file descriptor, none arrived"),
        (false, true) => bail!("this operation does not take a passed file descriptor"),
        _ => Ok(()),
    }
}

async fn dispatch(line: &str, fd: Option<OwnedFd>, writer: &mut OwnedWriteHalf) -> PrivResponse {
    match run(line, fd, writer).await {
        Ok((stdout, stderr)) => PrivResponse {
            ok: true,
            stdout,
            stderr,
            error: None,
        },
        Err(e) => PrivResponse {
            ok: false,
            stdout: String::new(),
            stderr: String::new(),
            error: Some(format!("{e:#}")),
        },
    }
}

/// Parse one request line, check it agrees with the descriptor that
/// arrived with it, and execute it.
///
/// Split out of [`dispatch`] so the three failure modes collapse into one
/// `Result` instead of three nested matches building the same struct.
async fn run(
    line: &str,
    fd: Option<OwnedFd>,
    writer: &mut OwnedWriteHalf,
) -> Result<(String, String)> {
    let req = serde_json::from_str::<PrivRequest>(line).context("parse request")?;
    check_fd_agreement(&req, fd.as_ref())?;
    exec(req, fd, writer).await
}

/// Write one `PrivEvent::Line` to the client. Best-effort: a write
/// failure is logged but doesn't abort the running subprocess.
async fn write_line_event(writer: &mut OwnedWriteHalf, stream: PrivStream, data: &str) {
    let event = PrivEvent::Line(PrivStreamLine {
        stream,
        data: data.to_owned(),
    });
    if let Ok(mut json) = serde_json::to_string(&event) {
        json.push('\n');
        if let Err(e) = writer.write_all(json.as_bytes()).await {
            tracing::warn!(error = %e, "write_line_event: write failed");
        }
    }
}

/// Execute a validated `PrivRequest`. Returns `(stdout, stderr)` on success.
/// For streaming ops (`CreateContainer`/`UpdateContainer` with `stream: true`)
/// output lines are forwarded to `writer` as `PrivEvent::Line` messages and
/// the returned strings are empty.
// One match arm per priv op — a flat 1:1 dispatch table. The length tracks
// the op count, not complexity; splitting it would just scatter the mapping.
#[allow(clippy::too_many_lines)]
/// Execute one validated request.
///
/// `fd` is the descriptor that arrived with this request, already checked
/// against the operation by [`check_fd_agreement`]: `Some` exactly for
/// the variants that stream into a caller-supplied descriptor, `None`
/// for every other operation.
async fn exec(
    req: PrivRequest,
    fd: Option<OwnedFd>,
    writer: &mut OwnedWriteHalf,
) -> Result<(String, String)> {
    match req {
        PrivRequest::StartContainer { ref name } => {
            validate_container_name(name)?;
            let machine = container_system_name(name);
            // Clear any start-limit lockout left by earlier failures so a
            // now-correct start isn't blocked. nixos-container start does not
            // do this itself. Best-effort: if the unit doesn't exist yet
            // (first-time create) reset-failed is a no-op and we proceed.
            let _ = Command::new("systemctl")
                .args(["reset-failed", &format!("container@{machine}.service")])
                .status()
                .await;
            container_run(&["start", &machine]).await
        }

        PrivRequest::StopContainer { ref name } => {
            validate_container_name(name)?;
            stop_and_release(&container_system_name(name)).await
        }

        PrivRequest::KillContainer { ref name } => {
            validate_container_name(name)?;
            // nixos-container has no kill verb. Use machinectl to send SIGKILL
            // to all processes in the container — the right semantics for a
            // forced shutdown after a graceful stop has already been attempted.
            let machine = container_system_name(name);
            machinectl_run(&["kill", &machine, "--signal=SIGKILL"]).await
        }

        PrivRequest::UpdateContainer { ref name, stream } => {
            container_flake_action("update", name, stream, writer).await
        }

        PrivRequest::CreateContainer { ref name, stream } => {
            container_flake_action("create", name, stream, writer).await
        }

        PrivRequest::DestroyContainer { ref name } => {
            validate_container_name(name)?;
            container_run(&["destroy", &container_system_name(name)]).await
        }

        PrivRequest::ListContainers => container_run(&["list"]).await,

        PrivRequest::ReadContainerJournal {
            ref container,
            ref query,
        } => {
            validate_container_system_name(container)?;
            read_container_journal(container, query).await
        }

        PrivRequest::WriteNspawnFlags {
            ref container,
            ref binds,
            ref isolation,
            ref load_credentials,
        } => handle_write_nspawn_flags(container, binds, isolation.as_ref(), load_credentials),

        PrivRequest::WriteResourceLimits {
            ref container,
            ref memory_max,
            ref cpu_quota,
            cpu_weight,
            io_weight,
        } => write_resource_limits(container, memory_max, cpu_quota, cpu_weight, io_weight),

        PrivRequest::RemoveServiceDropin { ref container } => remove_service_dropin(container),

        PrivRequest::DaemonReload => daemon_reload().await,

        PrivRequest::ReloadGatewayNginx => sync_gateway_nginx().await,

        PrivRequest::RunForgeAdmin { ref args } => {
            for arg in args {
                validate_forge_admin_arg(arg)?;
            }
            run_forge_admin(args).await
        }

        PrivRequest::SetAgentPaused {
            ref agent_name,
            paused,
        } => {
            validate_agent_name(agent_name)?;
            set_agent_paused(agent_name, paused)
        }

        PrivRequest::WriteAgentForgeToken {
            ref agent_name,
            ref token,
        } => {
            validate_agent_name(agent_name)?;
            write_agent_state_file(agent_name, "forge-token", &format!("{token}\n"))
        }

        PrivRequest::WriteAgentMatrixToken {
            ref agent_name,
            ref token,
            ref account,
            ref homeserver,
        } => {
            validate_agent_name(agent_name)?;
            // Build the token filename. `None` → the hive account's
            // `matrix-token`; `Some(a)` → `matrix-token-<a>`. The account
            // suffix MUST be validated as a plain identifier (no `/`, `.`,
            // `..`) before it goes into the filename, or a crafted account
            // could traverse out of the state dir — `write_agent_state_file`
            // trusts its `filename` argument.
            let filename = match account {
                None => "matrix-token".to_owned(),
                Some(a) => {
                    validate_name_chars(a)?;
                    format!("matrix-token-{a}")
                }
            };
            let res = write_agent_state_file(agent_name, &filename, &format!("{token}\n"))?;
            // For an extra account, persist its homeserver in a sidecar
            // (`matrix-account-<a>.json`) so the daemon can auto-discover the
            // account without a static `matrixAccounts` config entry. Only
            // when both `account` and `homeserver` are present; the account
            // suffix is already validated above.
            if let (Some(a), Some(hs)) = (account, homeserver) {
                let meta = serde_json::to_string(&MatrixAccountSidecar {
                    homeserver: hs.as_str(),
                })
                .context("serialize matrix account sidecar")?;
                write_agent_state_file(agent_name, &format!("matrix-account-{a}.json"), &meta)?;
            }
            Ok(res)
        }

        PrivRequest::WriteAgentGithubToken {
            ref agent_name,
            ref token,
        } => {
            validate_agent_name(agent_name)?;
            write_agent_state_file(agent_name, "github-token", &format!("{token}\n"))
        }

        PrivRequest::WriteAgentExtraForgeAccount {
            ref agent_name,
            ref label,
            ref base_url,
            ref token,
        } => {
            validate_agent_name(agent_name)?;
            validate_name_chars(label)?;
            let res = write_agent_state_file(
                agent_name,
                &format!("forge-{label}-token"),
                &format!("{token}\n"),
            )?;
            // Sidecar carries the base URL — there's no host-side nix config
            // for extra forges, so this is the only place it's persisted.
            let meta = serde_json::to_string(&ForgeSidecar {
                base_url: base_url.as_str(),
            })
            .context("serialize forge account sidecar")?;
            write_agent_state_file(agent_name, &format!("forge-{label}.json"), &meta)?;
            Ok(res)
        }

        PrivRequest::DeleteAgentExtraForgeAccount {
            ref agent_name,
            ref label,
        } => {
            validate_agent_name(agent_name)?;
            validate_name_chars(label)?;
            delete_agent_state_file(agent_name, &format!("forge-{label}-token"))?;
            delete_agent_state_file(agent_name, &format!("forge-{label}.json"))
        }

        PrivRequest::RestartMatrixDaemon { ref agent_name } => {
            restart_matrix_daemon(agent_name).await
        }

        PrivRequest::RegisterCiRunner { ref token } => register_ci_runner(token).await,

        PrivRequest::ControlInfraContainer { container, action } => {
            control_infra_container(container, action).await
        }

        PrivRequest::EnsureAgentSubvolume { ref agent_name } => {
            validate_agent_name(agent_name)?;
            ensure_agent_subvolume(agent_name).await
        }

        PrivRequest::DeleteAgentSubvolume { ref agent_name } => {
            validate_agent_name(agent_name)?;
            delete_agent_subvolume(agent_name).await
        }

        PrivRequest::EnsureBtrfsQuota => ensure_btrfs_quota().await,

        PrivRequest::ReadSubvolumeUsage { ref agent_name } => {
            validate_agent_name(agent_name)?;
            read_subvolume_usage(agent_name).await
        }

        PrivRequest::SetSubvolumeQuota {
            ref agent_name,
            limit_bytes,
        } => {
            validate_agent_name(agent_name)?;
            set_subvolume_quota(agent_name, limit_bytes).await
        }

        PrivRequest::UpgradeAgentSubvolume { ref agent_name } => {
            validate_agent_name(agent_name)?;
            upgrade_agent_subvolume(agent_name).await
        }

        PrivRequest::SnapshotAgentSubvolume {
            ref agent_name,
            ref snapshot_name,
        } => {
            validate_agent_name(agent_name)?;
            validate_snapshot_name(snapshot_name)?;
            snapshot_agent_subvolume(agent_name, snapshot_name).await
        }

        PrivRequest::DeleteAgentSnapshot {
            ref agent_name,
            ref snapshot_name,
        } => {
            validate_agent_name(agent_name)?;
            validate_snapshot_name(snapshot_name)?;
            delete_agent_snapshot(agent_name, snapshot_name).await
        }

        PrivRequest::SendAgentSnapshotToFile {
            ref agent_name,
            ref snapshot_name,
            ref parent_snapshot_name,
            ref dest_file_name,
        } => {
            validate_agent_name(agent_name)?;
            validate_snapshot_name(snapshot_name)?;
            if let Some(parent) = parent_snapshot_name {
                validate_snapshot_name(parent)?;
            }
            validate_credential_name(dest_file_name)?;
            send_agent_snapshot_to_file(
                agent_name,
                snapshot_name,
                parent_snapshot_name.as_deref(),
                dest_file_name,
            )
            .await
        }

        PrivRequest::SendAgentSnapshotToFd {
            ref agent_name,
            ref snapshot_name,
            ref parent_snapshot_name,
        } => {
            validate_agent_name(agent_name)?;
            validate_snapshot_name(snapshot_name)?;
            if let Some(parent) = parent_snapshot_name {
                validate_snapshot_name(parent)?;
            }
            let dest = fd.context("no descriptor to stream into")?;
            send_agent_snapshot_to_fd(
                agent_name,
                snapshot_name,
                parent_snapshot_name.as_deref(),
                dest,
            )
            .await
        }

        PrivRequest::SyncAgentTmpfiles { ref agents } => sync_agent_tmpfiles(agents).await,
    }
}

/// Shared body for `CreateContainer` / `UpdateContainer`: validate the
/// name, build the toplevel ourselves, and run
/// `nixos-container <verb> … --system-path <built>` (streaming line
/// events to `writer` when `stream` is set).
///
/// **Both verbs build explicitly now — not just `update`.** The first cut
/// of this fix only rewrote `update`, reasoning that `create` was already
/// safe: it wraps its whole action in an exclusive `flock` before calling
/// `nixos-container`'s own `buildFlake()`, and once `update` stopped
/// writing to `buildFlake()`'s shared `.tmp` out-link, concurrent
/// `create`s were the only remaining writers — mutually excluded by that
/// lock. True, but it leaves `create`'s safety resting on an internal
/// implementation detail of a script we don't own (its current locking
/// behavior, which could change upstream without notice) instead of on
/// something we control. Building here for both verbs removes `buildFlake()`
/// from the picture entirely — there's no shared `.tmp` left to race on,
/// so there's nothing left to reason about staying in sync with.
async fn container_flake_action(
    verb: &str,
    name: &str,
    stream: bool,
    writer: &mut OwnedWriteHalf,
) -> Result<(String, String)> {
    validate_container_name(name)?;
    // The build is the multi-minute phase of this operation — give it the
    // same live-line treatment `container_run_streaming` gives
    // `nixos-container` itself when the caller asked for it. Without
    // this, moving the build out of the streamed `nixos-container` call
    // (which is the whole point of this fix) would silently regress every
    // UI that shows build progress: nothing until the longest phase
    // finishes, then everything at once.
    let toplevel = nix_build_toplevel(name, stream.then_some(&mut *writer)).await?;
    let args = [
        verb,
        &container_system_name(name),
        "--system-path",
        &toplevel,
    ];
    if stream {
        container_run_streaming(&args, writer).await
    } else {
        container_run(&args).await
    }
}

/// The explicit `nixosConfigurations.<name>.config.system.build.toplevel`
/// flake attr path — same construction `hive-c0re`'s own
/// `lifecycle::prebuild_toplevel` uses, kept here as a pure function so
/// the exact string shape is unit-tested without needing to run `nix`.
fn toplevel_attr(name: &str) -> String {
    format!("{META_DIR}#nixosConfigurations.{name}.config.system.build.toplevel")
}

/// Build `nixosConfigurations.<name>.config.system.build.toplevel` and
/// return the resulting store path.
///
/// **Why hive-priv builds this itself instead of letting `nixos-container`
/// do it**: `nixos-container`'s own `buildFlake()` (invoked whenever
/// `--system-path` isn't passed) builds to a *hardcoded relative path* —
/// `$systemPath` is only ever assigned from the CLI flag or from its own
/// build result, so with no flag it stays `undef` and `"$systemPath.tmp"`
/// interpolates to the bare string `.tmp` in whatever the caller's cwd
/// is. `buildFlake()` itself takes no lock at all: `create` wraps its
/// *whole action* in an exclusive `flock` before calling it, but `update`
/// used to call it with no lock at all, so that `create`-side lock never
/// protected against a concurrent `update` clobbering the same `.tmp`.
/// hive-priv never sets a per-call cwd, so with
/// `services.hyperhive.c0re.buildSlots` > 1, two concurrent calls (any mix
/// of `create`/`update`) could share that one `.tmp`: one's
/// `readlink(".tmp")` resolving to the *other's* build output, handing an
/// agent's container the wrong agent's closure — the "agent container
/// gets closure of other agent" mystery bug.
///
/// Building the toplevel here and passing the resolved store path via
/// `--system-path` for *every* call means `buildFlake()` never runs at
/// all, for either verb — no shared `.tmp` left to race on, no locking
/// invariant of a script we don't own to keep track of. `--no-link`
/// avoids a competing out-link race of our own; we only need the store
/// path, not a GC root (the store path is safe from collection for as
/// long as it takes `nixos-container` to register it against the
/// container's own profile, same window every other consumer of a
/// `--print-out-paths` result already relies on).
///
/// **Forwards stderr live, captures stdout silently — deliberately not
/// symmetric.** This build is the multi-minute phase of a `create`/
/// `update`, and it used to run *inside* `nixos-container`'s own
/// `--flake` invocation, which streams every line to `writer` in real
/// time. Buffering it here (`Command::output()`, as this function first
/// shipped) regressed that: nothing on the wire — dashboard or
/// `journalctl -f` alike — until the whole build finishes, then
/// everything at once. So both pipes are drained concurrently (see the
/// in-body comments for why *both*, and why *concurrently*), but only
/// stderr — where nix's own progress goes — is forwarded to `writer` and
/// journald as it arrives, matching [`container_run_streaming`]'s shape.
/// stdout is different: `--print-out-paths` writes *only* the final store
/// path there, once, at the end — forwarding it the same way would risk
/// interleaving a progress line into the value this function hands back
/// as `--system-path`, trading a closure-mixup bug for a corrupted-
/// argument one. So stdout lines are accumulated silently and only
/// consulted after the exit status is known to be success.
///
/// `writer` is `None` for the non-streaming call shape (`stream: false`);
/// stderr still logs to journald either way, just without the
/// `PrivEvent::Line` forwarding.
async fn nix_build_toplevel(name: &str, mut writer: Option<&mut OwnedWriteHalf>) -> Result<String> {
    use tokio::io::AsyncBufReadExt as _;

    let attr = toplevel_attr(name);
    let args = [
        "--extra-experimental-features",
        "nix-command flakes",
        "build",
        "--no-link",
        "--print-out-paths",
        &attr,
    ];
    let mut child = Command::new("nix")
        .args(args)
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped())
        .spawn()
        .with_context(|| format!("invoke nix build {attr}"))?;

    let stdout = child.stdout.take().expect("stdout piped");
    let stderr = child.stderr.take().expect("stderr piped");
    let mut stdout_lines = BufReader::new(stdout).lines();
    let mut stderr_lines = BufReader::new(stderr).lines();

    let mut stdout_buf = String::new();
    let mut stderr_buf = String::new();

    // ⚠️ Both pipes are drained concurrently even though only one is
    // streamed: reading stderr alone would let stdout fill its pipe
    // buffer and deadlock the child on a build with enough stdout output
    // to fill it.
    //
    // ⚠️ Each stream's EOF is tracked separately rather than breaking on
    // the first `None`: `next_line()` on a closed stream returns
    // `Ok(None)` immediately and forever, so a loop that keeps polling a
    // finished stream spins hot until the other one ends too.
    let mut stdout_done = false;
    let mut stderr_done = false;
    while !(stdout_done && stderr_done) {
        tokio::select! {
            line = stdout_lines.next_line(), if !stdout_done => {
                match line {
                    // Captured, never streamed — this is the store path.
                    Ok(Some(l)) => {
                        stdout_buf.push_str(&l);
                        stdout_buf.push('\n');
                    }
                    Ok(None) => stdout_done = true,
                    Err(e) => {
                        tracing::warn!(error = %e, "nix build stdout read error");
                        stdout_done = true;
                    }
                }
            }
            line = stderr_lines.next_line(), if !stderr_done => {
                match line {
                    // Streamed as it arrives — the progress the dashboard
                    // and `journalctl -f` were missing.
                    Ok(Some(l)) => {
                        tracing::warn!(target: "nix-build-toplevel", "{l}");
                        if let Some(w) = writer.as_deref_mut() {
                            write_line_event(w, PrivStream::Stderr, &l).await;
                        }
                        if !stderr_buf.is_empty() {
                            stderr_buf.push('\n');
                        }
                        stderr_buf.push_str(&l);
                    }
                    Ok(None) => stderr_done = true,
                    Err(e) => {
                        tracing::warn!(error = %e, "nix build stderr read error");
                        stderr_done = true;
                    }
                }
            }
        }
    }

    // ⚠️ Success is decided by the exit status, not by "we parsed a
    // path" — a build can print to stdout and still fail.
    let status = child
        .wait()
        .await
        .with_context(|| format!("wait nix build {attr}"))?;
    if !status.success() {
        bail!(
            "nix build {attr} failed ({status}): {}",
            stderr_buf.lines().last().unwrap_or("").trim()
        );
    }
    // `--print-out-paths` prints one line *per output*, not one line
    // total: `nix build --no-link --print-out-paths nixpkgs#openssl`
    // prints two (`…-bin`, `…-man`). `config.system.build.toplevel` is
    // single-output today, so this is one line in practice — but a bare
    // `.trim()` would silently hand a multi-line string on to
    // `--system-path` the day that ever changes, which is the same
    // corrupted-argument failure this function exists to avoid. Require
    // exactly one line and error otherwise, so a future multi-output
    // attr fails loudly here instead of downstream in `nixos-container`.
    let lines: Vec<&str> = stdout_buf.lines().collect();
    let [path] = lines[..] else {
        bail!(
            "nix build {attr} produced {} output path(s), expected exactly 1: {stdout_buf:?}",
            lines.len()
        );
    };
    Ok(path.to_owned())
}

/// `WriteNspawnFlags` — validate the container + every bind path + every
/// credential entry, then write the container's nspawn flag overrides.
fn handle_write_nspawn_flags(
    container: &str,
    binds: &[BindMount],
    isolation: Option<&NetworkIsolation>,
    load_credentials: &[CredentialMount],
) -> Result<(String, String)> {
    validate_container_system_name(container)?;
    for bind in binds {
        validate_bind_path(&bind.host_path)?;
        validate_bind_path(&bind.container_path)?;
    }
    for cred in load_credentials {
        validate_credential_name(&cred.name)?;
        // Same path rules as binds (absolute, no colon/newline/quote/null):
        // the colon ban is essential since `--load-credential=name:path`
        // uses `:` as the name/path separator.
        validate_bind_path(&cred.host_path)?;
    }
    write_nspawn_flags(container, binds, isolation, load_credentials)?;
    Ok((String::new(), String::new()))
}

/// A btrfs snapshot label must start with `hive-` — this doubles as an
/// allow-list: only names hivectl itself constructs (or an operator who
/// knows the convention) can reach the `btrfs subvolume snapshot`/`delete`
/// shellouts, so an arbitrary caller can't use the snapshot ops to probe or
/// churn unrelated paths under `AGENT_STATE_ROOT`. Beyond the prefix, the
/// same charset restriction as [`validate_credential_name`] applies (it's
/// interpolated straight into a filesystem path).
fn validate_snapshot_name(name: &str) -> Result<()> {
    if !name.starts_with("hive-") {
        bail!("invalid snapshot label {name:?}: must start with \"hive-\"");
    }
    validate_credential_name(name)
}

/// A systemd credential id must be a short token — restrict to
/// `[A-Za-z0-9_-]` (no `.`) so it can't inject extra `--load-credential`
/// argv or break the `name:path` shape. `.` is deliberately excluded, not
/// just a bare `..`: this name gets interpolated into filesystem paths
/// (snapshot labels) and there's no legitimate need for a dot in either a
/// systemd credential id or a `hive-`-prefixed snapshot label — we're
/// defining this token format from scratch, so keep it maximally strict
/// rather than allow-then-patch each traversal-adjacent character
/// (mara: "we are making up the rules here, lets go strict").
fn validate_credential_name(name: &str) -> Result<()> {
    if name.is_empty()
        || !name
            .bytes()
            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'-'))
    {
        bail!("invalid credential name {name:?}: must be non-empty [A-Za-z0-9_-]");
    }
    Ok(())
}

/// `RemoveServiceDropin` — remove the container service's drop-in dir
/// if present (idempotent).
fn remove_service_dropin(container: &str) -> Result<(String, String)> {
    validate_container_system_name(container)?;
    let dir = format!("/run/systemd/system/container@{container}.service.d");
    if Path::new(&dir).exists() {
        std::fs::remove_dir_all(&dir).with_context(|| format!("remove {dir}"))?;
    }
    Ok((String::new(), String::new()))
}

/// `WriteResourceLimits` — drop the systemd resource settings into the
/// container service's drop-in dir, together with a
/// `ConditionPathIsDirectory=` guard on the agent's MCP runtime dir.
///
/// Two different kinds of setting land in the same file. `MemoryMax=` /
/// `CPUQuota=` are hard caps that throttle even on an idle host;
/// `CPUWeight=` / `IOWeight=` are cgroup v2 relative shares that only
/// decide who yields *under contention*. A weight of `None` means "not
/// configured" and omits the line, so a hive-c0re built before the weights
/// existed keeps producing the old two-line drop-in.
///
/// The condition causes systemd to *skip* (not *fail*) the unit when the
/// bind-mount source dir is absent — result is `condition`, which does not
/// increment the start-limit counter.  This is belt-and-braces on top of
/// the tmpfiles.d entries written by `SyncAgentTmpfiles`: in the unlikely
/// event the dir is missing at start time, the unit idles rather than
/// restart-looping into `start-limit-hit`.
fn write_resource_limits(
    container: &str,
    memory_max: &str,
    cpu_quota: &str,
    cpu_weight: Option<u32>,
    io_weight: Option<u32>,
) -> Result<(String, String)> {
    validate_container_system_name(container)?;
    // Derive the logical agent name (strip h- prefix) to form the runtime
    // dir path. Falls back to the full container name for infra containers
    // that don't use the h- prefix.
    let logical = container.strip_prefix(AGENT_PREFIX).unwrap_or(container);
    let runtime_dir = format!("{AGENT_RUNTIME_ROOT}/{logical}");
    let dir = format!("/run/systemd/system/container@{container}.service.d");
    std::fs::create_dir_all(&dir).with_context(|| format!("create {dir}"))?;
    let path = format!("{dir}/hyperhive-limits.conf");
    let content = limits_dropin_body(&runtime_dir, memory_max, cpu_quota, cpu_weight, io_weight);
    std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
    Ok((String::new(), String::new()))
}

/// How long a window the start-limit counts over, and how many starts it
/// allows inside it.
///
/// `container@.service` sets `Restart=on-failure` and **no** start limit, so
/// systemd's defaults apply: 5 starts per 10s, `RestartSec` 100ms. That
/// makes the bound depend on *how fast* a container dies — one that fails
/// instantly trips the limit in under a second, one that takes longer than
/// ~2s never trips it and restarts forever. Whether an agent gets bounded
/// is not meant to be a function of its failure speed.
///
/// The window has to exceed the worst-case time to burn the burst, or the
/// counter ages out between attempts and the limit is again unreachable:
/// `TimeoutStartSec` is 1min, so `BURST` slow failures plus their backoff
/// can span several minutes. 10min covers that with room.
///
/// Giving up is cheap here **because it is not terminal** — hive-c0re's
/// reconcile sweep retries later, and `reset-failed` (see `StartContainer`)
/// clears the latch first. That is what makes a tight burst safe.
const START_LIMIT_INTERVAL_SEC: u32 = 600;
/// One start plus two retries — the operator's ruling was "retry once or
/// twice", with the reconcile sweep as the slow path after that.
const START_LIMIT_BURST: u32 = 3;
/// Backoff between those retries. The 100ms default is for processes that
/// respawn instantly; a container that just failed to boot gains nothing
/// from being retried a tenth of a second later.
const RESTART_SEC: u32 = 5;

/// Render the body of `hyperhive-limits.conf`.
///
/// `[Unit]`: the condition is checked at start time — it skips (not fails)
/// the unit when the MCP socket dir is absent, avoiding restart loops —
/// plus the bounded start limit (see the constants above; `StartLimit*` are
/// `[Unit]` settings since systemd 229 and are silently ignored under
/// `[Service]`).
/// `[Service]`: the restart backoff, the hard caps, then the relative
/// weights. A weight of `None` means "not configured" and omits its line
/// entirely, so a request from a hive-c0re built before the weights
/// existed — or one whose nix option is `null` — renders no weight lines.
fn limits_dropin_body(
    runtime_dir: &str,
    memory_max: &str,
    cpu_quota: &str,
    cpu_weight: Option<u32>,
    io_weight: Option<u32>,
) -> String {
    // Built as two possibly-empty lines rather than pushed onto the
    // string: `format!` appended to a `String` trips clippy::pedantic's
    // `format_push_string`, and a `write!` would need an unwrap.
    let cpu_weight_line = cpu_weight.map_or_else(String::new, |w| format!("CPUWeight={w}\n"));
    let io_weight_line = io_weight.map_or_else(String::new, |w| format!("IOWeight={w}\n"));
    format!(
        "[Unit]\n\
         ConditionPathIsDirectory={runtime_dir}\n\
         StartLimitIntervalSec={START_LIMIT_INTERVAL_SEC}\n\
         StartLimitBurst={START_LIMIT_BURST}\n\
         \n\
         [Service]\n\
         RestartSec={RESTART_SEC}\n\
         MemoryMax={memory_max}\n\
         CPUQuota={cpu_quota}\n\
         {cpu_weight_line}{io_weight_line}"
    )
}

/// `DaemonReload` — `systemctl daemon-reload` on the host.
async fn daemon_reload() -> Result<(String, String)> {
    let out = Command::new("systemctl")
        .arg("daemon-reload")
        .output()
        .await
        .context("invoke systemctl daemon-reload")?;
    if !out.status.success() {
        bail!(
            "systemctl daemon-reload failed ({}): {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok((String::new(), String::new()))
}

/// `RestartMatrixDaemon` — restart the matrix daemon unit inside the
/// agent's container.
async fn restart_matrix_daemon(agent_name: &str) -> Result<(String, String)> {
    validate_agent_name(agent_name)?;
    let machine = format!("--machine=h-{agent_name}");
    let unit = "hive-matrix-daemon.service";
    let out = Command::new("systemctl")
        .args([&machine, "restart", unit])
        .output()
        .await
        .with_context(|| format!("systemctl restart {unit} in container h-{agent_name}"))?;
    if !out.status.success() {
        bail!(
            "systemctl restart {unit} in h-{agent_name} exited {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok((
        String::from_utf8_lossy(&out.stdout).into_owned(),
        String::from_utf8_lossy(&out.stderr).into_owned(),
    ))
}

/// Host path to the hive-ci runner's persisted registration credentials.
///
/// Paired with `hive-c0re`'s `forge::ci_runner::RUNNER_FILE`, which reads the
/// same file to decide whether a runner is registered and whether it still
/// names the configured forge host. Deliberately duplicated rather than shared:
/// `hive-priv` is the minimal root helper and does not depend on `hive-c0re`.
const RUNNER_CREDENTIALS: &str =
    "/var/lib/nixos-containers/hive-ci/var/lib/gitea-runner/hive/.runner";

/// Delete the runner's persisted credentials so upstream's `ExecStartPre` takes
/// its **absence** branch on the next start.
///
/// Absence is the state we want, so `NotFound` is success. Anything else — a
/// permission error above all — is NOT swallowed: it means the file is still
/// there, the restart will take upstream's already-registered branch, and the
/// caller would return `Ok` for a registration that never happened. That is the
/// same shape as a precondition that "passes" because it could not read the file
/// it was checking, and it is worth failing loudly to avoid.
///
/// Split from [`register_ci_runner`] purely so this rule is testable without a
/// container or a `systemctl`.
fn clear_runner_credentials(path: &str) -> Result<()> {
    match std::fs::remove_file(path) {
        Ok(()) => Ok(()),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(()),
        Err(e) => {
            Err(anyhow::Error::new(e).context(format!("remove stale runner credentials {path}")))
        }
    }
}

/// `RegisterCiRunner` — write the runner registration token to the host-side
/// `/run/hive-ci/runner-token` env-file, then restart the in-container runner
/// so it re-registers. The forge admin token never enters the container; only
/// the registration token c0re passes here is written, and it lands on a host
/// path bind-mounted read-only into hive-ci.
async fn register_ci_runner(token: &str) -> Result<(String, String)> {
    use std::os::unix::fs::PermissionsExt as _;
    // Reject anything that could corrupt the `KEY=VALUE` env-file or smuggle a
    // second line — a forge registration token is an opaque single-line string.
    if token.is_empty() || token.contains(['\n', '\r', '\0']) {
        bail!("ci runner registration token empty or contains control characters");
    }
    let token_path = "/run/hive-ci/runner-token";
    // In-place truncate+write of the existing inode (mirrors the prefetch's
    // `echo > $FILE`), NOT a temp+rename: nspawn pins this file's inode into
    // hive-ci at container start, so a rename would leave the running runner
    // reading the old content. Format + perms match the tmpfiles seed and the
    // prefetch: `TOKEN=<tok>`, mode 0600, root-owned.
    std::fs::write(token_path, format!("TOKEN={token}\n"))
        .with_context(|| format!("write {token_path}"))?;
    std::fs::set_permissions(token_path, std::fs::Permissions::from_mode(0o600))
        .with_context(|| format!("chmod {token_path}"))?;
    // Remove the persisted credentials BEFORE restarting, or the restart is a
    // no-op as far as registration goes.
    //
    // Upstream's `ExecStartPre` only re-registers when `.runner` is absent, the
    // labels changed, or the *registration token hash* changed — never when the
    // instance URL changed. c0re only calls this helper once it has already
    // decided the existing credentials are absent or stale
    // (`forge::ci_runner::ensure_ci_runner_registered` returns early otherwise),
    // so by the time we are here a re-registration is exactly what is wanted and
    // deleting the file is the narrow way to guarantee it happens.
    //
    // Writing a fresh token is NOT sufficient on its own: whether the hash
    // changes depends on whether the forge mints a new registration token per
    // request or hands back a stable one, which is Forgejo's behaviour to
    // choose and change. Gating our remediation on the absence branch — the one
    // upstream evaluates unconditionally — makes that question moot instead of
    // load-bearing.
    //
    // See [`clear_runner_credentials`] for why absence is the branch we aim at
    // and why only `NotFound` counts as success.
    clear_runner_credentials(RUNNER_CREDENTIALS)?;
    // Restart the in-container runner so it reads the new token and registers.
    let out = Command::new("systemctl")
        .args(["--machine=hive-ci", "restart", "gitea-runner-hive.service"])
        .output()
        .await
        .context("systemctl restart gitea-runner-hive.service in hive-ci")?;
    if !out.status.success() {
        bail!(
            "systemctl restart gitea-runner-hive.service in hive-ci exited {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok((
        String::from_utf8_lossy(&out.stdout).into_owned(),
        String::from_utf8_lossy(&out.stderr).into_owned(),
    ))
}

/// `ControlInfraContainer` — start/stop/restart a hive infrastructure
/// service via `systemctl <verb> <unit>`. The [`InfraContainer`] enum is
/// the allowlist: serde already rejected any unknown / unsafe name
/// (hive-c0re has no variant, so a stop can't sever the daemon socket) at
/// deserialisation, so no root-side `.contains()` check is needed here.
/// Serves both the hive-wide `hivectl stop`/`start` flow and an
/// `infra_admin` agent's `restart` (action = Restart).
///
/// ⚠️ The unit is derived from the variant, never sent by the caller —
/// which is what keeps this from being a general `systemctl` pass-through.
/// It is not always `container@<name>.service`: the gateway resolves to the
/// host's `nginx.service`.
async fn control_infra_container(
    container: InfraContainer,
    action: InfraAction,
) -> Result<(String, String)> {
    let verb = action.systemctl_verb();
    let unit = container.service_unit();
    let out = Command::new("systemctl")
        .args([verb, &unit])
        .output()
        .await
        .with_context(|| format!("systemctl {verb} {unit}"))?;
    if !out.status.success() {
        bail!(
            "systemctl {verb} {unit} exited {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(target: "infra-control", "{verb} {unit}");
    Ok((
        String::from_utf8_lossy(&out.stdout).into_owned(),
        String::from_utf8_lossy(&out.stderr).into_owned(),
    ))
}

/// Create/overwrite `dir/filename` at 0600 without following a symlink at the
/// leaf, returning the open fd for the caller to `fchown`. `filename` must be a
/// single plain component (no `/`, `.`, `..`) — the leaf sits in an
/// agent-writable dir, so `O_NOFOLLOW` refuses a planted symlink (`ELOOP`)
/// instead of letting this root-privileged write/chmod be redirected at another
/// file; `O_WRONLY` refuses a directory leaf (`EISDIR`); `O_TRUNC` keeps the
/// overwrite semantics for an existing regular file. `.mode(0o600)` sets the
/// create mode; the explicit `fchmod` after (on the fd, not a re-resolved path)
/// tightens an already-existing file and dodges umask. The returned fd is the
/// exact inode the write hit, so the caller's `fchown` is TOCTOU-immune.
fn write_state_file_nofollow(dir: &Path, filename: &str, content: &str) -> Result<std::fs::File> {
    use std::io::Write as _;
    use std::os::unix::fs::{OpenOptionsExt as _, PermissionsExt as _};

    if filename.is_empty() || filename == "." || filename == ".." || filename.contains('/') {
        bail!("write_state_file_nofollow: refusing non-plain filename {filename:?}");
    }
    let path = dir.join(filename);
    let mut file = std::fs::OpenOptions::new()
        .write(true)
        .create(true)
        .truncate(true)
        .mode(0o600)
        .custom_flags(libc::O_NOFOLLOW)
        .open(&path)
        .with_context(|| format!("open (no-follow) {}", path.display()))?;
    file.write_all(content.as_bytes())
        .with_context(|| format!("write {}", path.display()))?;
    file.set_permissions(std::fs::Permissions::from_mode(0o600))
        .with_context(|| format!("chmod 600 {}", path.display()))?;
    Ok(file)
}

/// Sidecar written alongside an extra matrix account's token
/// (`matrix-account-<name>.json`) so `hive-matrix-mcp` can auto-discover
/// the account's homeserver without a static `matrixAccounts` config
/// entry. Read side: `hive-matrix-mcp/src/accounts.rs`'s
/// `read_account_homeserver` (deliberately reads via a bare
/// `serde_json::Value` rather than this shape — that side treats a
/// malformed/missing sidecar as "skip this account" rather than an
/// error, so it stays loosely typed; this side is the one place the
/// file is written, so it gets the precise shape).
#[derive(Serialize)]
struct MatrixAccountSidecar<'a> {
    homeserver: &'a str,
}

/// Sidecar written alongside a dashboard-provisioned extra forge
/// account's token (`forge-<label>.json`) so `hive-forge` can resolve
/// the account's base URL. Read side: `hive-forge/src/client.rs`'s own
/// (separately defined, deserialize-only) `ForgeSidecar` — same field
/// name (`base_url`), no shared crate between `hive-priv` and
/// `hive-forge` to hang a common type off, so the two structs are
/// pinned to the same JSON key by convention, not by the compiler.
#[derive(Serialize)]
struct ForgeSidecar<'a> {
    base_url: &'a str,
}

/// Shared helper for `WriteAgentForgeToken` and `WriteAgentMatrixToken`.
/// Writes `content` to `AGENT_STATE_ROOT/<agent_name>/state/<filename>`,
/// chowns to the agent user (derived from the state dir's existing owner),
/// and chmods 0600. Running as root (hive-priv), so this succeeds
/// regardless of the file's prior owner/permissions.
fn write_agent_state_file(
    agent_name: &str,
    filename: &str,
    content: &str,
) -> Result<(String, String)> {
    let state_dir = PathBuf::from(AGENT_STATE_ROOT)
        .join(agent_name)
        .join("state");
    write_agent_dir_file(agent_name, &state_dir, filename, content)
}

/// Create or remove an agent's pause marker under its harness dir. The
/// marker is written empty and chowned to the harness dir's owner (the
/// agent), matching how the harness itself would have created it.
///
/// Both directions are idempotent: re-pausing truncates the existing empty
/// marker rather than failing, and a `NotFound` on removal is the
/// already-resumed case, not an error.
fn set_agent_paused(agent_name: &str, paused: bool) -> Result<(String, String)> {
    let harness_dir = PathBuf::from(AGENT_STATE_ROOT)
        .join(agent_name)
        .join("harness");
    if paused {
        return write_agent_dir_file(agent_name, &harness_dir, PAUSED_MARKER_FILE, "");
    }
    remove_marker_in(&harness_dir, PAUSED_MARKER_FILE)?;
    tracing::info!(agent = %agent_name, "cleared pause marker");
    Ok((String::new(), String::new()))
}

/// Unlink `dir/filename`, treating "already gone" as success.
///
/// `remove_file` unlinks the leaf itself and never follows a symlink, so an
/// agent-planted link at the marker path cannot redirect this root unlink
/// at another file — the same threat `write_state_file_nofollow` closes on
/// the create side.
fn remove_marker_in(dir: &Path, filename: &str) -> Result<()> {
    let path = dir.join(filename);
    match std::fs::remove_file(&path) {
        Ok(()) => Ok(()),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(()),
        Err(e) => Err(e).with_context(|| format!("remove {}", path.display())),
    }
}

/// Write `content` to `dir/filename` as root, chowning the result to `dir`'s
/// owner so the agent process can read it back. Shared by the credential
/// writes (which target `state/`) and the pause marker (which targets
/// `harness/`) — both write into a directory owned by the agent, which is
/// precisely why they need hive-priv at all.
fn write_agent_dir_file(
    agent_name: &str,
    dir: &Path,
    filename: &str,
    content: &str,
) -> Result<(String, String)> {
    use std::os::fd::AsRawFd as _;
    use std::os::unix::fs::MetadataExt as _;

    let state_dir = dir.to_path_buf();
    // NOTE: `create_dir_all` is normally a no-op — lifecycle creates and chowns
    // the state dir during spawn. On the rare edge where the dir doesn't exist
    // yet (container being provisioned for the first time), the newly created dir
    // is root:root. The `stat state_dir` chown below will then see uid=0 and
    // leave the file root-owned (0600). The agent won't be able to read it until
    // its lifecycle completes. If that happens, a `systemctl restart hive-c0re`
    // after provisioning will re-mint and re-write the token correctly.
    std::fs::create_dir_all(&state_dir)
        .with_context(|| format!("create state dir {}", state_dir.display()))?;

    // Security-critical: refuses a symlink the (state/-owning) agent may have
    // planted at the leaf, so this root-privileged create/write/chmod/chown
    // can't be redirected at an arbitrary file. See `write_state_file_nofollow`.
    let path = state_dir.join(filename);
    let file = write_state_file_nofollow(&state_dir, filename, content)?;

    // Chown to the state dir's owner so the agent process can read the file.
    // fchown on the same fd — TOCTOU-immune (the inode the write hit, never a
    // swapped path). If stat fails (e.g. dir just created, owner is root), the
    // file stays root-owned and 0600 — still unreadable by others, just not
    // agent-readable. Log a warning so operators can diagnose.
    match std::fs::metadata(&state_dir) {
        Ok(meta) => {
            // SAFETY: `file` is an open, owned fd live for the whole call;
            // `fchown` only mutates that inode's uid/gid.
            let rc = unsafe { libc::fchown(file.as_raw_fd(), meta.uid(), meta.gid()) };
            if rc != 0 {
                let e = std::io::Error::last_os_error();
                tracing::warn!(
                    agent = %agent_name,
                    path = %path.display(),
                    error = %e,
                    "write_agent_state_file: fchown failed"
                );
            }
        }
        Err(e) => {
            tracing::warn!(
                agent = %agent_name,
                error = %e,
                "write_agent_state_file: stat state_dir failed, leaving file root-owned"
            );
        }
    }
    tracing::info!(
        agent = %agent_name,
        dir = %state_dir.display(),
        file = %filename,
        "wrote agent file"
    );
    Ok((String::new(), String::new()))
}

/// Remove `AGENT_STATE_ROOT/<agent_name>/state/<filename>` if present.
/// Idempotent revoke counterpart to [`write_agent_state_file`] — a
/// missing file is success, not an error. `filename` must be a single
/// plain component (no `/`, `.`, `..`); callers pass a pre-validated
/// label into a fixed `forge-<label>-token` shape, same as the write
/// side.
fn delete_agent_state_file(agent_name: &str, filename: &str) -> Result<(String, String)> {
    if filename.is_empty() || filename == "." || filename == ".." || filename.contains('/') {
        bail!("delete_agent_state_file: refusing non-plain filename {filename:?}");
    }
    let path = PathBuf::from(AGENT_STATE_ROOT)
        .join(agent_name)
        .join("state")
        .join(filename);
    match std::fs::remove_file(&path) {
        Ok(()) => {
            tracing::info!(agent = %agent_name, file = %filename, "removed agent state file");
        }
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
        Err(e) => return Err(e).with_context(|| format!("remove {}", path.display())),
    }
    Ok((String::new(), String::new()))
}

/// btrfs superblock magic, as reported by `statfs(2)`'s `f_type`.
const BTRFS_SUPER_MAGIC: i64 = 0x9123_683E;

/// Inode number of a btrfs subvolume root (`BTRFS_FIRST_FREE_OBJECTID`).
/// Every subvolume's top directory has this inode; plain directories do
/// not, so `statfs == btrfs && st_ino == 256` reliably identifies a
/// subvolume root.
const BTRFS_SUBVOL_ROOT_INO: u64 = 256;

/// Whether `path` lives on a btrfs filesystem (via `statfs(2)`).
fn is_on_btrfs(path: &Path) -> Result<bool> {
    use std::os::unix::ffi::OsStrExt as _;
    let c_path = std::ffi::CString::new(path.as_os_str().as_bytes())
        .with_context(|| format!("path {} has an interior null byte", path.display()))?;
    // SAFETY: `c_path` is a valid NUL-terminated C string that outlives the
    // call; `statfs` only writes into the zero-initialised `buf`.
    let mut buf: libc::statfs = unsafe { std::mem::zeroed() };
    let rc = unsafe { libc::statfs(c_path.as_ptr(), &raw mut buf) };
    if rc != 0 {
        return Err(std::io::Error::last_os_error())
            .with_context(|| format!("statfs {}", path.display()));
    }
    Ok(buf.f_type == BTRFS_SUPER_MAGIC)
}

/// Whether `path` is the root of a btrfs subvolume (on btrfs and inode 256).
fn is_btrfs_subvolume(path: &Path) -> bool {
    use std::os::unix::fs::MetadataExt as _;
    let on_btrfs = is_on_btrfs(path).unwrap_or(false);
    let ino_match = std::fs::metadata(path).is_ok_and(|m| m.ino() == BTRFS_SUBVOL_ROOT_INO);
    on_btrfs && ino_match
}

/// `EnsureAgentSubvolume` — make the agent's state root a btrfs subvolume
/// when the FS supports it. Idempotent + progressive: no-op when the root
/// already exists or the FS isn't btrfs. See the wire doc on the variant.
async fn ensure_agent_subvolume(agent_name: &str) -> Result<(String, String)> {
    use std::os::unix::fs::MetadataExt as _;

    let root = PathBuf::from(AGENT_STATE_ROOT);
    let agent_root = root.join(agent_name);

    // Progressive: existing agents (plain dir OR already a subvol) are left
    // untouched — never auto-migrated.
    if agent_root.exists() {
        return Ok((String::new(), String::new()));
    }

    // Only btrfs supports subvolumes; on anything else hive-c0re's normal
    // `create_dir_all` makes a plain dir (the pre-subvolume behaviour). The
    // parent must exist for both statfs and `btrfs subvolume create`.
    std::fs::create_dir_all(&root)
        .with_context(|| format!("create agents root {}", root.display()))?;
    if !is_on_btrfs(&root)? {
        return Ok((String::new(), String::new()));
    }

    let out = Command::new("btrfs")
        .args(["subvolume", "create"])
        .arg(&agent_root)
        .output()
        .await
        .with_context(|| format!("spawn btrfs subvolume create {}", agent_root.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs subvolume create {} failed: {}",
            agent_root.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }

    // The subvol root is created root-owned, but hive-c0re (the `hive-core`
    // user) must be able to mkdir state/ claude/ harness/ inside it — exactly
    // as it would in a plain dir. Chown it to AGENT_STATE_ROOT's owner
    // (hive-core). This MUST succeed: a root-owned subvol would make the
    // downstream dir creation fail with a confusing permission error, and the
    // c0re-side exists-check would then skip re-running this op on retry,
    // wedging the agent. So on any failure roll the subvol back and bail — the
    // create path surfaces a clear error and a retry starts clean.
    let chown_result = std::fs::metadata(&root)
        .with_context(|| format!("stat agents root {} for ownership", root.display()))
        .and_then(|meta| {
            std::os::unix::fs::chown(&agent_root, Some(meta.uid()), Some(meta.gid())).with_context(
                || format!("chown subvol {} to agents-root owner", agent_root.display()),
            )
        });
    if let Err(e) = chown_result {
        // Best-effort rollback so we never leave a root-owned subvol behind.
        let _ = Command::new("btrfs")
            .args(["subvolume", "delete"])
            .arg(&agent_root)
            .output()
            .await;
        return Err(e.context(format!(
            "rolled back subvolume {} after chown failed",
            agent_root.display()
        )));
    }
    tracing::info!(agent = %agent_name, path = %agent_root.display(), "created agent state subvolume");
    Ok((String::new(), String::new()))
}

/// `DeleteAgentSubvolume` — delete the agent's state root iff it's a btrfs
/// subvolume (purge path only). No-op for plain dirs / missing paths;
/// hive-c0re's own `remove_dir_all` covers those. See the wire doc.
async fn delete_agent_subvolume(agent_name: &str) -> Result<(String, String)> {
    let agent_root = PathBuf::from(AGENT_STATE_ROOT).join(agent_name);
    if !is_btrfs_subvolume(&agent_root) {
        return Ok((String::new(), String::new()));
    }
    let out = Command::new("btrfs")
        .args(["subvolume", "delete"])
        .arg(&agent_root)
        .output()
        .await
        .with_context(|| format!("spawn btrfs subvolume delete {}", agent_root.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs subvolume delete {} failed: {}",
            agent_root.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(agent = %agent_name, path = %agent_root.display(), "deleted agent state subvolume");
    Ok((String::new(), String::new()))
}

/// `EnsureBtrfsQuota` — enable btrfs qgroup accounting on the filesystem
/// holding `AGENT_STATE_ROOT`. Idempotent + statfs-gated (no-op off btrfs).
/// Operator opt-in only; see the wire doc.
async fn ensure_btrfs_quota() -> Result<(String, String)> {
    let root = PathBuf::from(AGENT_STATE_ROOT);
    std::fs::create_dir_all(&root)
        .with_context(|| format!("create agents root {}", root.display()))?;
    if !is_on_btrfs(&root)? {
        // Non-btrfs host: quota/qgroups don't apply. No-op success so the
        // operator-facing verb degrades cleanly.
        return Ok((
            String::new(),
            "filesystem is not btrfs — quota not applicable".to_owned(),
        ));
    }
    let out = Command::new("btrfs")
        .args(["quota", "enable"])
        .arg(&root)
        .output()
        .await
        .with_context(|| format!("spawn btrfs quota enable {}", root.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs quota enable {} failed: {}",
            root.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(path = %root.display(), "enabled btrfs qgroup accounting");
    Ok((String::new(), String::new()))
}

/// `ReadSubvolumeUsage` — return an agent subvolume's qgroup rows
/// (`btrfs qgroup show -f --raw <…/agent_name>`) verbatim in stdout for
/// hive-c0re to parse. `-f` lists the qgroups impacting the given path,
/// excluding ancestral qgroups (per btrfs-qgroup-show(8)) — so it scopes
/// to this subvolume and never mixes in other agents'. hive-c0re then
/// selects the level-0 (`0/<subvolid>`) leaf row. See the wire doc.
async fn read_subvolume_usage(agent_name: &str) -> Result<(String, String)> {
    let agent_root = PathBuf::from(AGENT_STATE_ROOT).join(agent_name);
    let out = Command::new("btrfs")
        .args(["qgroup", "show", "-f", "--raw"])
        .arg(&agent_root)
        .output()
        .await
        .with_context(|| format!("spawn btrfs qgroup show {}", agent_root.display()))?;
    if !out.status.success() {
        // The common failure is "quota not enabled" — pass the stderr
        // through so hive-c0re can surface it gracefully.
        bail!(
            "btrfs qgroup show {} failed: {}",
            agent_root.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    Ok((
        String::from_utf8_lossy(&out.stdout).into_owned(),
        String::new(),
    ))
}

/// Best-effort removal of a leftover migration path from a prior aborted
/// upgrade: try `btrfs subvolume delete` (in case it's a half-created
/// subvolume) then a plain recursive remove. Both failures are ignored —
/// the path may simply not exist.
async fn cleanup_stale_path(path: &Path) {
    if path.exists() {
        let _ = Command::new("btrfs")
            .args(["subvolume", "delete"])
            .arg(path)
            .output()
            .await;
        let _ = std::fs::remove_dir_all(path);
    }
}

/// Stage a populated subvolume at `tmp` mirroring `agent_root`: create the
/// subvolume, copy `agent_root`'s contents into it preserving
/// ownership/permissions/xattrs, then match the subvolume root's owner + mode
/// to the original. On any failure the partially-staged `tmp` is cleaned up
/// (so the caller can bail with the original dir still untouched).
async fn stage_upgrade_subvolume(agent_root: &Path, tmp: &Path) -> Result<()> {
    use std::os::unix::fs::{MetadataExt as _, PermissionsExt as _};

    // Fresh subvolume to receive the copy.
    let out = Command::new("btrfs")
        .args(["subvolume", "create"])
        .arg(tmp)
        .output()
        .await
        .with_context(|| format!("spawn btrfs subvolume create {}", tmp.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs subvolume create {} failed: {}",
            tmp.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }

    // Copy contents preserving everything (`-a` = --preserve=all → mode,
    // ownership, timestamps, links, xattrs); reflink for fast CoW clones on the
    // same btrfs. `<src>/.` copies the directory's contents (incl. dotfiles)
    // into the subvolume rather than nesting it.
    let copy = Command::new("cp")
        .arg("-a")
        .arg("--reflink=auto")
        .arg(format!("{}/.", agent_root.display()))
        .arg(tmp)
        .output()
        .await
        .with_context(|| format!("spawn cp into {}", tmp.display()))?;
    if !copy.status.success() {
        cleanup_stale_path(tmp).await;
        bail!(
            "copy {} -> {} failed (original left untouched): {}",
            agent_root.display(),
            tmp.display(),
            String::from_utf8_lossy(&copy.stderr).trim()
        );
    }

    // Match the new subvolume root's ownership + mode to the original dir.
    // `cp -a <src>/.` copies the *contents* but the subvolume root keeps its
    // create-time root ownership, so set it explicitly — the swapped-in
    // subvolume must be indistinguishable from the original to hive-c0re.
    let apply = std::fs::metadata(agent_root)
        .with_context(|| format!("stat {} for ownership", agent_root.display()))
        .and_then(|m| {
            std::os::unix::fs::chown(tmp, Some(m.uid()), Some(m.gid()))
                .with_context(|| format!("chown {} to match original", tmp.display()))?;
            std::fs::set_permissions(tmp, std::fs::Permissions::from_mode(m.mode()))
                .with_context(|| format!("chmod {} to match original", tmp.display()))?;
            Ok(())
        });
    if let Err(e) = apply {
        cleanup_stale_path(tmp).await;
        return Err(e.context("upgrade aborted before swap; original left untouched"));
    }
    Ok(())
}

/// `UpgradeAgentSubvolume` — convert an existing plain-dir agent state root
/// into a btrfs subvolume in place. Operator opt-in; the caller (hivectl)
/// stops the agent first and restarts it after. See the wire doc.
///
/// Migration: stage a sibling subvolume mirroring the dir
/// ([`stage_upgrade_subvolume`]), then rename the original aside and the
/// subvolume into place, then remove the original. Any failure before the
/// rename-swap leaves the original dir untouched.
async fn upgrade_agent_subvolume(agent_name: &str) -> Result<(String, String)> {
    let root = PathBuf::from(AGENT_STATE_ROOT);
    let agent_root = root.join(agent_name);

    if !agent_root.exists() {
        // A crash between the two swap renames (original → `.<name>.old`
        // succeeded, `.<name>.migrating` → agent_root did not) leaves the
        // agent root missing but the original data intact under `.<name>.old`.
        // Point at the recovery rather than a bare "nothing to do" so the
        // operator isn't left guessing where the data went.
        let old = root.join(format!(".{agent_name}.old"));
        if old.exists() {
            bail!(
                "no state dir at {agent} — but {old} holds the original data from an \
                 interrupted upgrade (host crashed mid-swap). Restore it with \
                 `mv {old} {agent}`, then re-run the upgrade.",
                agent = agent_root.display(),
                old = old.display(),
            );
        }
        bail!(
            "no state dir to upgrade at {} — nothing to do",
            agent_root.display()
        );
    }
    // Idempotent: already a subvolume → nothing to do.
    if is_btrfs_subvolume(&agent_root) {
        return Ok((String::new(), String::new()));
    }
    if !is_on_btrfs(&root)? {
        bail!(
            "{} is not on btrfs — subvolumes are unsupported, cannot upgrade",
            root.display()
        );
    }

    // Sibling temp paths on the same filesystem (so the copy can reflink and
    // the swap renames are atomic). Leading dots keep them out of the agent
    // namespace (`validate_agent_name` rejects dot-prefixed names).
    let tmp = root.join(format!(".{agent_name}.migrating"));
    let old = root.join(format!(".{agent_name}.old"));
    // Clear any debris from a previously interrupted run before starting.
    cleanup_stale_path(&tmp).await;
    cleanup_stale_path(&old).await;

    stage_upgrade_subvolume(&agent_root, &tmp).await?;

    // Swap. `rename` is atomic within a filesystem. The window between the
    //    two renames is the only unsafe point: a crash there leaves the agent
    //    root missing but both `.old` (original) and the new subvolume present
    //    — recoverable by hand, hence the loud logging.
    if let Err(e) = std::fs::rename(&agent_root, &old) {
        cleanup_stale_path(&tmp).await;
        return Err(anyhow::Error::new(e).context(format!(
            "rename {} -> {} failed; original left untouched",
            agent_root.display(),
            old.display()
        )));
    }
    if let Err(e) = std::fs::rename(&tmp, &agent_root) {
        // Restore the original from its renamed-aside copy.
        let restored = std::fs::rename(&old, &agent_root).is_ok();
        cleanup_stale_path(&tmp).await;
        return Err(anyhow::Error::new(e).context(format!(
            "rename {} -> {} failed; original {}",
            tmp.display(),
            agent_root.display(),
            if restored {
                "restored"
            } else {
                "COULD NOT BE RESTORED — manual recovery needed"
            }
        )));
    }

    // 5. Success: drop the original (a plain dir) and report.
    if let Err(e) = std::fs::remove_dir_all(&old) {
        // The migration succeeded; a leftover `.old` is cosmetic. Warn only.
        tracing::warn!(
            agent = %agent_name, path = %old.display(),
            "upgraded subvolume but failed to remove old dir: {e}"
        );
    }
    tracing::info!(
        agent = %agent_name, path = %agent_root.display(),
        "upgraded agent state dir to btrfs subvolume"
    );
    Ok((
        format!("upgraded {} to a btrfs subvolume", agent_root.display()),
        String::new(),
    ))
}

/// Derive a snapshot's path from the agent name + label: a dot-prefixed
/// sibling of the agent's state root so it can never collide with a real
/// agent directory (`validate_agent_name` rejects dot-prefixed names).
fn snapshot_path(agent_name: &str, snapshot_name: &str) -> PathBuf {
    PathBuf::from(AGENT_STATE_ROOT).join(format!(".{agent_name}.snapshot.{snapshot_name}"))
}

/// `SnapshotAgentSubvolume` — create a read-only btrfs snapshot of an
/// agent's state subvolume, for `btrfs send` to stream from during
/// inter-hive migration. See the wire doc.
async fn snapshot_agent_subvolume(
    agent_name: &str,
    snapshot_name: &str,
) -> Result<(String, String)> {
    let agent_root = PathBuf::from(AGENT_STATE_ROOT).join(agent_name);
    if !is_btrfs_subvolume(&agent_root) {
        bail!(
            "{} is not a btrfs subvolume — nothing to snapshot (run `hivectl agent <name> subvol upgrade` first)",
            agent_root.display()
        );
    }
    let snap = snapshot_path(agent_name, snapshot_name);
    if snap.exists() {
        bail!(
            "snapshot {} already exists — delete it first or pick a different name",
            snap.display()
        );
    }
    let out = Command::new("btrfs")
        .args(["subvolume", "snapshot", "-r"])
        .arg(&agent_root)
        .arg(&snap)
        .output()
        .await
        .with_context(|| {
            format!(
                "spawn btrfs subvolume snapshot -r {} {}",
                agent_root.display(),
                snap.display()
            )
        })?;
    if !out.status.success() {
        bail!(
            "btrfs subvolume snapshot -r {} {} failed: {}",
            agent_root.display(),
            snap.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(
        agent = %agent_name, snapshot = %snap.display(),
        "created read-only agent state snapshot"
    );
    Ok((snap.display().to_string(), String::new()))
}

/// `DeleteAgentSnapshot` — delete a previously-created read-only snapshot.
/// No-op if the path doesn't exist. See the wire doc.
async fn delete_agent_snapshot(agent_name: &str, snapshot_name: &str) -> Result<(String, String)> {
    let snap = snapshot_path(agent_name, snapshot_name);
    if !snap.exists() {
        return Ok((String::new(), String::new()));
    }
    let out = Command::new("btrfs")
        .args(["subvolume", "delete"])
        .arg(&snap)
        .output()
        .await
        .with_context(|| format!("spawn btrfs subvolume delete {}", snap.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs subvolume delete {} failed: {}",
            snap.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(agent = %agent_name, snapshot = %snap.display(), "deleted agent state snapshot");
    Ok((String::new(), String::new()))
}

/// `SendAgentSnapshotToFile` — stream a read-only snapshot (optionally
/// incremental against `parent_name`) to a file under
/// `MIGRATE_STAGING_ROOT` via `btrfs send`. Local-file half of the
/// inter-hive migration transport; see `PrivRequest::SendAgentSnapshotToFile`
/// for the cross-hive follow-up.
async fn send_agent_snapshot_to_file(
    agent_name: &str,
    snapshot_name: &str,
    parent_name: Option<&str>,
    dest_file_name: &str,
) -> Result<(String, String)> {
    let snap = snapshot_path(agent_name, snapshot_name);
    if !snap.exists() {
        bail!(
            "snapshot {} does not exist — create it with `subvol snapshot create` first",
            snap.display()
        );
    }

    std::fs::create_dir_all(MIGRATE_STAGING_ROOT)
        .with_context(|| format!("create {MIGRATE_STAGING_ROOT}"))?;
    let dest = Path::new(MIGRATE_STAGING_ROOT).join(dest_file_name);
    // `create_new` (O_CREAT|O_EXCL) makes the no-overwrite guarantee atomic
    // instead of a check-then-create race against a concurrent request.
    let dest_file = match std::fs::File::options()
        .write(true)
        .create_new(true)
        .open(&dest)
    {
        Ok(f) => f,
        Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => bail!(
            "{} already exists — pick a different destination or remove it first \
             (send never overwrites an existing export)",
            dest.display()
        ),
        Err(e) => {
            return Err(e).with_context(|| format!("create {}", dest.display()));
        }
    };

    let mut cmd = Command::new("btrfs");
    cmd.arg("send");
    if let Some(parent) = parent_name {
        let parent_path = snapshot_path(agent_name, parent);
        if !parent_path.exists() {
            bail!(
                "parent snapshot {} does not exist — pick an existing parent or omit it for a full send",
                parent_path.display()
            );
        }
        cmd.arg("-p").arg(&parent_path);
    }
    cmd.arg(&snap);
    cmd.stdout(std::process::Stdio::from(dest_file));
    cmd.stderr(std::process::Stdio::piped());

    let out = cmd
        .spawn()
        .with_context(|| format!("spawn btrfs send {}", snap.display()))?
        .wait_with_output()
        .await
        .with_context(|| format!("wait on btrfs send {}", snap.display()))?;
    if !out.status.success() {
        // Clean up a partial/failed export so a retry doesn't trip the
        // "already exists" guard on garbage. Best-effort: warn (don't fail
        // the whole call over it) if removal itself fails, so a stuck
        // partial file that later masquerades as a completed export is at
        // least visible in the log.
        if let Err(rm_err) = std::fs::remove_file(&dest) {
            tracing::warn!(
                dest = %dest.display(), error = %rm_err,
                "failed to remove partial export after btrfs send failure — \
                 next attempt at this dest will hit the already-exists guard"
            );
        }
        bail!(
            "btrfs send {} failed: {}",
            snap.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(
        agent = %agent_name, snapshot = %snap.display(), dest = %dest.display(),
        parent = ?parent_name, "exported agent snapshot to file"
    );
    Ok((dest.display().to_string(), String::new()))
}

/// `SendAgentSnapshotToFd` — stream a read-only snapshot (optionally
/// incremental against `parent_name`) straight into a descriptor the
/// caller passed us.
///
/// The network half of the inter-hive migration transport, arranged so
/// this helper never learns there *is* a network: hive-c0re connects to
/// the peer's snapshot store, writes the header itself, and hands the
/// connected socket over. We only ever see "a thing to write bytes into",
/// which keeps a root process out of any address, protocol or trust
/// decision — and keeps everyone out of the data path once `btrfs send`
/// starts, which matters at multi-gigabyte sizes.
async fn send_agent_snapshot_to_fd(
    agent_name: &str,
    snapshot_name: &str,
    parent_name: Option<&str>,
    dest: OwnedFd,
) -> Result<(String, String)> {
    let snap = snapshot_path(agent_name, snapshot_name);
    if !snap.exists() {
        bail!(
            "snapshot {} does not exist — create it with `subvol snapshot create` first",
            snap.display()
        );
    }

    let mut cmd = Command::new("btrfs");
    cmd.arg("send");
    if let Some(parent) = parent_name {
        let parent_path = snapshot_path(agent_name, parent);
        if !parent_path.exists() {
            bail!(
                "parent snapshot {} does not exist — pick an existing parent or omit it for a full send",
                parent_path.display()
            );
        }
        cmd.arg("-p").arg(&parent_path);
    }
    cmd.arg(&snap);
    cmd.stdout(std::process::Stdio::from(dest));
    cmd.stderr(std::process::Stdio::piped());

    let out = cmd
        .spawn()
        .with_context(|| format!("spawn btrfs send {}", snap.display()))?
        .wait_with_output()
        .await
        .with_context(|| format!("wait on btrfs send {}", snap.display()))?;
    if !out.status.success() {
        // Nothing to clean up: the destination isn't ours. A partial
        // stream is the receiving end's problem, and `btrfs receive`
        // refuses to commit an incomplete subvolume anyway.
        bail!(
            "btrfs send {} failed: {}",
            snap.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(
        agent = %agent_name, snapshot = %snap.display(), parent = ?parent_name,
        "streamed agent snapshot into a passed descriptor"
    );
    Ok((String::new(), String::new()))
}

/// `SetSubvolumeQuota` — set or clear a qgroup size limit on an agent
/// subvolume (`btrfs qgroup limit <bytes|none> <…/agent_name>`). See the
/// wire doc.
async fn set_subvolume_quota(
    agent_name: &str,
    limit_bytes: Option<u64>,
) -> Result<(String, String)> {
    let agent_root = PathBuf::from(AGENT_STATE_ROOT).join(agent_name);
    let limit = limit_bytes.map_or_else(|| "none".to_owned(), |n| n.to_string());
    let out = Command::new("btrfs")
        .args(["qgroup", "limit", &limit])
        .arg(&agent_root)
        .output()
        .await
        .with_context(|| format!("spawn btrfs qgroup limit {}", agent_root.display()))?;
    if !out.status.success() {
        bail!(
            "btrfs qgroup limit {limit} {} failed: {}",
            agent_root.display(),
            String::from_utf8_lossy(&out.stderr).trim()
        );
    }
    tracing::info!(agent = %agent_name, %limit, "set agent subvolume quota");
    Ok((String::new(), String::new()))
}

/// Validate a single argument destined for `forgejo admin`. Rejects
/// null bytes and newlines (which could corrupt the subprocess args list
/// or log output). Shell metacharacters are harmless since the command
/// is spawned directly (no shell), but we reject them defensively.
fn validate_forge_admin_arg(arg: &str) -> Result<()> {
    if arg.bytes().any(|b| b == 0 || b == b'\n' || b == b'\r') {
        bail!("forge admin arg {arg:?} contains null byte or newline");
    }
    Ok(())
}

/// Redact a line before it hits the (root-readable, but still
/// unnecessarily exposed) host journal.
///
/// Two independent rules, because the previous single rule failed open.
/// It matched only the substring "password", chosen to be robust against
/// forgejo *rewording* its password line — and the leak arrived from the
/// other axis entirely: a **different kind of secret** on a differently
/// worded line. `forgejo admin user generate-access-token` prints
/// `Access token was successfully created: <40 hex>`, which contains no
/// "password" and went to the journal verbatim for every agent ever
/// provisioned.
///
/// So the second rule matches on **shape, not vocabulary**: a long
/// unbroken run of secret-alphabet characters. A new secret type is then
/// caught by default rather than by someone remembering to add a keyword.
///
/// ⚠️ This deliberately over-matches. A nix store hash is also a long
/// opaque run and will redact its line. That is the correct direction to
/// be wrong in: the cost of a false positive is one less log line, and
/// the cost of a false negative is a live credential in a journal that
/// any `read_host_journal` holder can read.
fn redact_secret_line(line: &str) -> std::borrow::Cow<'_, str> {
    if line.to_ascii_lowercase().contains("password") {
        return std::borrow::Cow::Borrowed("[redacted: line mentions a password]");
    }
    if contains_secret_shaped_run(line) {
        return std::borrow::Cow::Borrowed("[redacted: line contains a secret-shaped token]");
    }
    std::borrow::Cow::Borrowed(line)
}

/// True when the line contains an unbroken run of at least 32 characters
/// from the hex / base64url alphabet. 32 sits below forgejo's 40-hex
/// access token and above the ordinary words and path segments that
/// appear in `forgejo admin` output.
///
/// ⚠️ Scans for a RUN, not for a whitespace-delimited word. An earlier
/// version split on whitespace and required the whole word to match,
/// which a secret with punctuation glued to it defeats: `"<token>,"` and
/// `"[<token>]"` both fail an all-chars check on the word while still
/// containing the credential in full. Whitespace is not what delimits a
/// secret — the alphabet is (thanks @argus for catching it).
fn contains_secret_shaped_run(line: &str) -> bool {
    const MIN: usize = 32;
    let mut run = 0usize;
    for b in line.bytes() {
        if b.is_ascii_alphanumeric() || matches!(b, b'+' | b'/' | b'=' | b'_' | b'-') {
            run += 1;
            if run >= MIN {
                return true;
            }
        } else {
            run = 0;
        }
    }
    false
}

/// Run `forgejo admin <args>` inside the `hive-forge` container as the
/// `forgejo` unix user. Requires root (for nsenter into the container's
/// namespaces). Returns `(stdout, stderr)`.
async fn run_forge_admin(args: &[String]) -> Result<(String, String)> {
    let mut cmd_args: Vec<&str> = vec![
        "run",
        "hive-forge",
        "--",
        "runuser",
        "-u",
        "forgejo",
        "--",
        "forgejo",
        "--work-path",
        "/var/lib/forgejo",
        "admin",
    ];
    for a in args {
        cmd_args.push(a.as_str());
    }
    let out = Command::new("nixos-container")
        .args(&cmd_args)
        .output()
        .await
        .context("invoke nixos-container run hive-forge -- forgejo admin")?;
    let stdout = String::from_utf8_lossy(&out.stdout).into_owned();
    let stderr = String::from_utf8_lossy(&out.stderr).into_owned();
    // stdout at DEBUG, not INFO: on the success path this stream carries
    // the *product* of the command (the freshly minted token, the created
    // user's details) and nothing an operator needs at default verbosity.
    // Redaction stays on as the second layer — the level decides who sees
    // it, the redactor decides what it says, and neither alone is enough.
    for line in stdout.lines() {
        tracing::debug!(target: "forgejo-admin", "{}", redact_secret_line(line));
    }
    for line in stderr.lines() {
        tracing::warn!(target: "forgejo-admin", "{}", redact_secret_line(line));
    }
    if !out.status.success() {
        // Redact here too. The error string is propagated to the caller and
        // ends up logged; a partial-failure stderr can carry the same
        // material stdout would have. Redacting the log but not the error
        // is the same "two of three sites" gap that makes these leaks
        // survive a fix.
        let safe_stderr: String = stderr
            .lines()
            .map(|l| redact_secret_line(l).into_owned())
            .collect::<Vec<_>>()
            .join("; ");
        bail!(
            "forgejo admin {} failed ({}): {}",
            args.join(" "),
            out.status,
            safe_stderr.trim()
        );
    }
    Ok((stdout, stderr))
}

/// Invoke `nixos-container` with the given args, log output to journald.
async fn container_run(args: &[&str]) -> Result<(String, String)> {
    let out = Command::new("nixos-container")
        .args(args)
        .output()
        .await
        .context("invoke nixos-container")?;
    let stdout = String::from_utf8_lossy(&out.stdout).into_owned();
    let stderr = String::from_utf8_lossy(&out.stderr).into_owned();
    // `list` is a read-only enumeration called on the hot path (dashboard
    // rescan, forge + boot sweeps) — its stdout is the return value, not
    // progress, so logging every container name on every call floods the
    // journal. Log stdout only for the mutating ops, where each line is
    // genuine progress. stderr is always logged (errors matter regardless).
    if args.first() != Some(&"list") {
        for line in stdout.lines() {
            tracing::info!(target: "nixos-container", "{line}");
        }
    }
    for line in stderr.lines() {
        tracing::warn!(target: "nixos-container", "{line}");
    }
    if !out.status.success() {
        bail!(
            "nixos-container {} failed ({}): {}",
            args.join(" "),
            out.status,
            stderr.trim()
        );
    }
    Ok((stdout, stderr))
}

/// Invoke `machinectl` with the given args, log output to journald.
/// Used for operations that nixos-container doesn't expose (e.g. sending
/// signals to running containers).
async fn machinectl_run(args: &[&str]) -> Result<(String, String)> {
    let out = Command::new("machinectl")
        .args(args)
        .output()
        .await
        .context("invoke machinectl")?;
    let stdout = String::from_utf8_lossy(&out.stdout).into_owned();
    let stderr = String::from_utf8_lossy(&out.stderr).into_owned();
    for line in stdout.lines() {
        tracing::info!(target: "machinectl", "{line}");
    }
    for line in stderr.lines() {
        tracing::warn!(target: "machinectl", "{line}");
    }
    if !out.status.success() {
        bail!(
            "machinectl {} failed ({}): {}",
            args.join(" "),
            out.status,
            stderr.trim()
        );
    }
    Ok((stdout, stderr))
}

/// How long to wait for machined to drop a machine's registration after a
/// shutdown has been asked for. Generous: a container with slow-stopping
/// units legitimately takes a while, and escalating early would SIGKILL a
/// shutdown that was going to finish on its own.
const NAME_RELEASE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(20);

/// Poll cadence while waiting for the registration to go away.
const NAME_RELEASE_POLL: std::time::Duration = std::time::Duration::from_millis(500);

/// Cap on a single registration probe. The probe is a D-Bus round trip to
/// machined; if machined itself is wedged the call would otherwise sit on
/// the D-Bus method timeout, which is far longer than the whole stop
/// sequence should take.
const MACHINE_PROBE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(5);

/// True when machined still holds a registration for `machine`.
///
/// This asks machined the same question the registration itself answers —
/// `machinectl show` resolves the name through `GetMachine`, the very lookup
/// that makes a later boot fail with `Failed to register machine: already
/// exists`. So a positive answer here is exactly the condition that breaks
/// the next start, not a proxy for it.
///
/// Deliberately NOT the container's systemd unit state: the unit can be
/// `inactive` while the registration is still held, and that gap is the
/// whole bug this probe exists to catch.
///
/// Errors and timeouts answer "still registered". Being wrong that way costs
/// a redundant SIGKILL to something already gone; being wrong the other way
/// hands back a stop that silently leaked the name.
async fn machine_registered(machine: &str) -> bool {
    let probe = Command::new("machinectl")
        .args(["show", machine, "--property=Name"])
        // Don't leave a probe behind when the timeout below fires.
        .kill_on_drop(true)
        .output();
    match tokio::time::timeout(MACHINE_PROBE_TIMEOUT, probe).await {
        Ok(Ok(out)) => out.status.success(),
        Ok(Err(e)) => {
            tracing::warn!(%machine, error = %e, "machinectl show failed to run; assuming still registered");
            true
        }
        Err(_) => {
            tracing::warn!(%machine, "machinectl show timed out; assuming still registered");
            true
        }
    }
}

/// Poll [`machine_registered`] until the name is free or the timeout expires.
/// Returns true once the registration is gone.
async fn wait_name_released(machine: &str) -> bool {
    let deadline = tokio::time::Instant::now() + NAME_RELEASE_TIMEOUT;
    loop {
        if !machine_registered(machine).await {
            return true;
        }
        if tokio::time::Instant::now() >= deadline {
            return false;
        }
        tokio::time::sleep(NAME_RELEASE_POLL).await;
    }
}

/// Stop `machine` and only report success once machined has actually released
/// the name.
///
/// `nixos-container stop` exiting 0 does not mean the machine is gone. A
/// process that sits in the machine's cgroup without being a child of the
/// container's init — a shell exec'd in from outside, say — never receives
/// the shutdown's SIGTERM if it has been stopped with SIGSTOP, so the
/// registration outlives the "successful" stop. Every later start of that
/// container then fails with `Failed to register machine: already exists`,
/// and machined re-persists the stale record across its own restart, so
/// there is no cleaning it up after the fact. The only place to catch it is
/// here, in the stop.
///
/// So: ask for the stop, wait for the name, and fail loudly if it is still
/// held — a caller that is told the stop worked will go on to start the
/// container and hit the confusing registration error instead of this one.
///
/// This used to escalate to `machinectl kill --signal=SIGKILL` here. Dropped
/// per real incident data: the case this guards is a container genuinely
/// wedged (e.g. a root-login process survived the stop), and SIGKILL
/// doesn't recover that in practice — only a host-level reboot has.
/// Pretending a kill attempt handled it hides a condition that needs a human
/// to look at the host, so this now just reports the failure instead of
/// quietly (and ineffectually) trying to force it.
///
/// The verify-then-fail lives in the helper rather than at a call site so
/// that every stop gets it: dashboard, reconcile, destroy, cold-start
/// fallback. The start path already distrusts its own exit code the same way;
/// this is the missing half of that pair.
async fn stop_and_release(machine: &str) -> Result<(String, String)> {
    let stop = container_run(&["stop", machine]).await;
    if wait_name_released(machine).await {
        // Happy path, and also the path where a stop that reported failure
        // nonetheless brought the machine down. Either way the caller gets
        // the original result untouched.
        return stop;
    }

    tracing::error!(
        %machine,
        "stop finished but machined still holds the registration — the \
         container is likely wedged (a process outside its init tree \
         survived the stop); this needs a host-level look, not another \
         stop attempt"
    );
    bail!(
        "stop {machine}: machined still holds the machine name after {}s. \
         This container is likely wedged and starting it again will fail to \
         register — needs host-level intervention (a reboot has been the \
         only reliable fix in practice).",
        NAME_RELEASE_TIMEOUT.as_secs()
    )
}

/// Invoke `nixos-container` with the given args and forward output lines
/// to the caller as `PrivEvent::Line` messages in real time, logging each
/// line to journald as it arrives. Returns `(String::new(), String::new())`
/// on success (all output was streamed); the error string includes stderr
/// tail on failure.
async fn container_run_streaming(
    args: &[&str],
    writer: &mut OwnedWriteHalf,
) -> Result<(String, String)> {
    use tokio::io::AsyncBufReadExt as _;
    use tokio::process::Command;

    let mut child = Command::new("nixos-container")
        .args(args)
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped())
        .spawn()
        .context("invoke nixos-container (streaming)")?;

    let stdout = child.stdout.take().expect("stdout piped");
    let stderr = child.stderr.take().expect("stderr piped");

    let mut stdout_lines = BufReader::new(stdout).lines();
    let mut stderr_lines = BufReader::new(stderr).lines();

    // Collect stderr for the error message; stream both to the client.
    let mut stderr_buf = String::new();

    // Drive stdout and stderr concurrently. `tokio::select!` interleaves
    // them without bias — both streams drain at roughly the same rate
    // as the subprocess produces output.
    loop {
        tokio::select! {
            line = stdout_lines.next_line() => {
                match line {
                    Ok(Some(l)) => {
                        tracing::info!(target: "nixos-container", "{l}");
                        write_line_event(writer, PrivStream::Stdout, &l).await;
                    }
                    Ok(None) => break,
                    Err(e) => {
                        tracing::warn!(error = %e, "nixos-container stdout read error");
                        break;
                    }
                }
            }
            line = stderr_lines.next_line() => {
                match line {
                    Ok(Some(l)) => {
                        tracing::warn!(target: "nixos-container", "{l}");
                        write_line_event(writer, PrivStream::Stderr, &l).await;
                        if !stderr_buf.is_empty() {
                            stderr_buf.push('\n');
                        }
                        stderr_buf.push_str(&l);
                    }
                    Ok(None) => {}
                    Err(e) => {
                        tracing::warn!(error = %e, "nixos-container stderr read error");
                    }
                }
            }
        }
    }

    // Drain any remaining stderr after stdout closed.
    while let Ok(Some(l)) = stderr_lines.next_line().await {
        tracing::warn!(target: "nixos-container", "{l}");
        write_line_event(writer, PrivStream::Stderr, &l).await;
        if !stderr_buf.is_empty() {
            stderr_buf.push('\n');
        }
        stderr_buf.push_str(&l);
    }

    let status = child.wait().await.context("wait nixos-container")?;
    if !status.success() {
        // Only the last stderr line is embedded — the full stderr was
        // already forwarded line-by-line as PrivEvent::Line messages and
        // is captured in build_logs.sqlite by the caller. Keeping the
        // error message short avoids bloating the anyhow chain.
        bail!(
            "nixos-container {} failed ({}): {}",
            args.join(" "),
            status,
            stderr_buf.lines().last().unwrap_or("").trim()
        );
    }
    Ok((String::new(), String::new()))
}

/// Read a container's journal as root via `journalctl -M`. Returns
/// `(stdout, stderr)`. Unlike `container_run` a non-zero exit is *not* a
/// hard error — journalctl's own diagnostic (folded into `stderr` with
/// the exit status) is what the caller surfaces to the operator, so the
/// helper never bails.
async fn read_container_journal(container: &str, query: &JournalQuery) -> Result<(String, String)> {
    let mut args: Vec<String> = vec![
        "-M".to_owned(),
        container.to_owned(),
        "--no-pager".to_owned(),
        format!("--output={}", query.output.as_journalctl()),
        "-n".to_owned(),
        query.lines.to_string(),
    ];
    if query.boot {
        args.push("-b".to_owned());
    }
    if let Some(u) = &query.unit {
        args.push("-u".to_owned());
        args.push(u.clone());
    }
    if let Some(p) = &query.priority {
        args.push("-p".to_owned());
        args.push(p.clone());
    }
    // `--grep=`/`--since=`/`--until=` use the `=`-joined form so a value
    // can never be parsed as a separate journalctl flag.
    if let Some(g) = &query.grep {
        args.push(format!("--grep={g}"));
    }
    if let Some(s) = &query.since {
        args.push(format!("--since={s}"));
    }
    if let Some(u) = &query.until {
        args.push(format!("--until={u}"));
    }
    let out = Command::new("journalctl")
        .args(&args)
        .output()
        .await
        .context("invoke journalctl -M")?;
    let stdout = String::from_utf8_lossy(&out.stdout).into_owned();
    let stderr = if out.status.success() {
        String::from_utf8_lossy(&out.stderr).into_owned()
    } else {
        format!(
            "journalctl -M {container} exited {}: {}",
            out.status,
            String::from_utf8_lossy(&out.stderr).trim()
        )
    };
    Ok((stdout, stderr))
}

/// Synchronise the host's nginx unit after an `agents.conf` write.
///
/// Queries `ActiveState` and dispatches:
/// - `active`  → `systemctl reload nginx` (SIGHUP, zero-downtime)
/// - `failed`  → `systemctl reset-failed nginx` + `systemctl start nginx`
/// - otherwise → `systemctl start nginx`
///
/// ⚠️ `nginx` is hard-coded on purpose — see `PrivRequest::ReloadGatewayNginx`.
/// The unit name is the scope of this verb: nginx is a host unit, so no
/// namespace bounds it and the literal is the only thing standing between
/// "reload the gateway" and "reload anything".
///
/// Returns `(String::new(), String::new())` on success so it fits the
/// `exec` return type directly.
async fn sync_gateway_nginx() -> Result<(String, String)> {
    let state_out = Command::new("systemctl")
        .args(["show", "--property=ActiveState", "--value", "nginx"])
        .output()
        .await
        .context("query gateway nginx ActiveState")?;
    if !state_out.status.success() {
        tracing::warn!(
            exit_code = ?state_out.status.code(),
            stderr = %String::from_utf8_lossy(&state_out.stderr).trim(),
            "systemctl show ActiveState exited non-zero — gateway nginx may be down"
        );
    }
    let state = String::from_utf8_lossy(&state_out.stdout).trim().to_owned();
    // State-aware dispatch: reload when running; reset+start after
    // start-limit failure; plain start when inactive or unknown.
    match state.as_str() {
        "active" => {
            let out = Command::new("systemctl")
                .args(["reload", "nginx"])
                .output()
                .await
                .context("reload gateway nginx")?;
            if !out.status.success() {
                bail!(
                    "gateway nginx reload failed ({}): {}",
                    out.status,
                    String::from_utf8_lossy(&out.stderr).trim()
                );
            }
        }
        "failed" => {
            // Clear start-limit so the next start can proceed.
            let _ = Command::new("systemctl")
                .args(["reset-failed", "nginx"])
                .status()
                .await;
            let out = Command::new("systemctl")
                .args(["start", "nginx"])
                .output()
                .await
                .context("start gateway nginx after reset-failed")?;
            if !out.status.success() {
                bail!(
                    "gateway nginx start (after reset-failed) failed ({}): {}",
                    out.status,
                    String::from_utf8_lossy(&out.stderr).trim()
                );
            }
        }
        _ => {
            // inactive, activating, deactivating, unknown — just start.
            let out = Command::new("systemctl")
                .args(["start", "nginx"])
                .output()
                .await
                .context("start gateway nginx")?;
            if !out.status.success() {
                bail!(
                    "gateway nginx start failed (state={state:?}) ({}): {}",
                    out.status,
                    String::from_utf8_lossy(&out.stderr).trim()
                );
            }
        }
    }
    Ok((String::new(), String::new()))
}

/// Return the system container name for a logical agent name.
/// All agents (including the manager) use the `h-` prefix.
fn container_system_name(name: &str) -> String {
    format!("{AGENT_PREFIX}{name}")
}

/// Validate a logical agent name (the name hive-c0re uses internally,
/// before the `h-` container prefix is applied).
fn validate_agent_name(name: &str) -> Result<()> {
    validate_name_chars(name)?;
    Ok(())
}

/// Validate a logical agent name and check it maps to a hive-managed container.
fn validate_container_name(name: &str) -> Result<()> {
    if SIBLING_CONTAINERS.contains(&name) {
        return Ok(());
    }
    validate_name_chars(name)?;
    Ok(())
}

/// Validate a system-level container name (already has `h-` prefix for
/// all agents including the manager, or is a sibling service name).
fn validate_container_system_name(name: &str) -> Result<()> {
    if SIBLING_CONTAINERS.contains(&name) {
        return Ok(());
    }
    if let Some(suffix) = name.strip_prefix(AGENT_PREFIX) {
        validate_name_chars(suffix)?;
        return Ok(());
    }
    bail!("container name {name:?} is not managed by hive");
}

fn validate_name_chars(name: &str) -> Result<()> {
    if name.is_empty()
        || !name
            .chars()
            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-')
    {
        bail!("invalid name {name:?}: must be non-empty lowercase ascii + digits + hyphens");
    }
    Ok(())
}

/// Validate a bind-mount path: must be absolute, non-empty, and contain
/// no newlines, null bytes, or double-quotes (which would break the
/// `EXTRA_NSPAWN_FLAGS="..."` conf line format).
fn validate_bind_path(path: &str) -> Result<()> {
    if path.is_empty()
        || !path.starts_with('/')
        || path
            .bytes()
            .any(|b| b == 0 || b == b'\n' || b == b'"' || b == b':')
    {
        bail!(
            "invalid bind path {path:?}: must be an absolute path with no colons, newlines, null bytes, or double-quotes"
        );
    }
    Ok(())
}

/// Update `/etc/nixos-containers/<container>.conf`: strips network-isolation
/// vars (`PRIVATE_NETWORK`, `HOST_ADDRESS*`, `LOCAL_ADDRESS*`, `HOST_BRIDGE`,
/// Update `/etc/nixos-containers/<container>.conf`: strip old network vars,
/// write network isolation settings, then append `EXTRA_NSPAWN_FLAGS`.
/// When `isolation` is `Some`, writes `PRIVATE_NETWORK=1` + veth wiring;
/// when `None`, writes `PRIVATE_NETWORK=0`.
/// `--tmpfs=<mount>/.git` for every bound git repo, hiding its metadata
/// from inside the container.
///
/// Two kinds of mount qualify, for one reason: **the agent is given a
/// working tree, never a repository.** `/knowledge` is the hive's shared
/// docs — whose `.git/config` has held a credential the host-side worker
/// embedded — and `/agents/<name>/config` is a config repo, an agent's own
/// or a parent's read-only view of a child's. In both cases `.git` carries
/// every branch and the full history of a document whose *currently
/// deployed* value is the only thing a reader may act on, and an abandoned
/// branch is indistinguishable from a live one.
///
/// An overlay rather than an exported copy: there is no second tree to
/// keep in sync, so nothing can go stale, and no code path has to remember
/// to refresh it.
///
/// ⚠️ Ordering matters — these must be appended **after** the `--bind`
/// flags so nspawn mounts them on top of the already-mounted trees.
/// Config mounts are matched by shape, not by a name list: the set is
/// dynamic, growing with each child bound into a parent.
fn git_overlay_flags(binds: &[BindMount]) -> Vec<String> {
    binds
        .iter()
        .map(|b| b.container_path.as_str())
        .filter(|p| *p == "/knowledge" || (p.starts_with("/agents/") && p.ends_with("/config")))
        .map(|p| format!("--tmpfs={p}/.git"))
        .collect()
}

fn write_nspawn_flags(
    container: &str,
    binds: &[BindMount],
    isolation: Option<&NetworkIsolation>,
    load_credentials: &[CredentialMount],
) -> Result<()> {
    use std::fmt::Write as _;
    let path = format!("/etc/nixos-containers/{container}.conf");
    let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
    let lines: Vec<&str> = original
        .lines()
        .filter(|line| {
            let t = line.trim_start();
            !t.starts_with("EXTRA_NSPAWN_FLAGS=")
                && !t.starts_with("PRIVATE_NETWORK=")
                && !t.starts_with("HOST_ADDRESS=")
                && !t.starts_with("LOCAL_ADDRESS=")
                && !t.starts_with("HOST_ADDRESS6=")
                && !t.starts_with("LOCAL_ADDRESS6=")
                && !t.starts_with("HOST_BRIDGE=")
        })
        .collect();
    let mut out = lines.join("\n");
    if !out.is_empty() {
        out.push('\n');
    }
    if let Some(iso) = isolation {
        out.push_str("PRIVATE_NETWORK=1\n");
        // HOST_ADDRESS = the bridge gateway IP. nixos-container's
        // container-side setup only installs a default route
        // (`ip route add default via $HOST_ADDRESS`) when HOST_ADDRESS is
        // non-empty; leaving it blank gave the container an address but no
        // route off the bridge subnet (no internet, no api.anthropic.com).
        // In bridge mode (HOST_BRIDGE set) the host-side address/route
        // setup is skipped, so this only affects the container's route —
        // exactly what we want.
        let _ = writeln!(out, "HOST_ADDRESS={}", iso.gateway_ip);
        // LOCAL_ADDRESS is intentionally empty: agent containers receive their
        // IP dynamically via DHCP from the bridge dnsmasq pool.  HOST_ADDRESS
        // (the gateway IP) is still written so nixos-container's container-side
        // init installs a default route before the DHCP lease arrives.
        out.push_str("LOCAL_ADDRESS=\n");
        out.push_str("HOST_ADDRESS6=\n");
        out.push_str("LOCAL_ADDRESS6=\n");
        let _ = writeln!(out, "HOST_BRIDGE={}", iso.bridge);
    } else {
        out.push_str("PRIVATE_NETWORK=0\n");
        out.push_str("HOST_ADDRESS=\n");
        out.push_str("LOCAL_ADDRESS=\n");
        out.push_str("HOST_ADDRESS6=\n");
        out.push_str("LOCAL_ADDRESS6=\n");
        out.push_str("HOST_BRIDGE=\n");
    }
    let mut flags: Vec<String> = binds
        .iter()
        .map(|b| {
            let flag = if b.read_only { "--bind-ro" } else { "--bind" };
            format!("{flag}={}:{}", b.host_path, b.container_path)
        })
        .collect();
    flags.extend(git_overlay_flags(binds));
    // Credential forwarding: nspawn loads each host secret into the
    // container's credential store under `<name>`; inner units inherit it
    // via `LoadCredential=<name>`. Validated (name charset + bind-path
    // rules) in handle_write_nspawn_flags above.
    for cred in load_credentials {
        flags.push(format!(
            "--load-credential={}:{}",
            cred.name, cred.host_path
        ));
    }
    let flags_joined = flags.join(" ");
    let _ = writeln!(out, "EXTRA_NSPAWN_FLAGS=\"{flags_joined}\"");
    std::fs::write(&path, out).with_context(|| format!("write {path}"))?;

    // DNS marker for the in-container resolver oneshot. nixos-container
    // copies the *host's* /etc/resolv.conf into the container at every
    // start (its host resolver — e.g. 127.0.0.53 — is unreachable from a
    // private netns, and isn't authoritative for the hive's own zones
    // anyway). The `hyperhive-isolated-dns` oneshot in harness-base.nix
    // rewrites resolv.conf to point at the bridge resolver, but only when
    // this marker exists; it carries the gateway IP so the container
    // doesn't have to re-derive it. Written on isolate, removed otherwise,
    // so the same shared container toplevel behaves correctly in both modes.
    write_bridge_dns_marker(container, isolation)?;
    Ok(())
}

/// Path to the in-container DNS marker (the container's own `/etc`).
fn bridge_dns_marker_path(container: &str) -> String {
    format!("/var/lib/nixos-containers/{container}/etc/hyperhive-bridge-dns")
}

/// Write (isolated) or remove (host-netns) the bridge-DNS marker the
/// `hyperhive-isolated-dns` oneshot keys off. The marker file contains
/// just the gateway IP. Best-effort on removal (absence is the goal).
fn write_bridge_dns_marker(container: &str, isolation: Option<&NetworkIsolation>) -> Result<()> {
    let path = bridge_dns_marker_path(container);
    match isolation {
        Some(iso) => {
            // On a fresh install the container's `/etc` may not exist yet
            // (rootfs not fully materialised before the first start), so
            // `write` would fail with ENOENT. Create the parent dir first
            // — it's the container's own `/etc`, which nixos-container
            // populates on start; a pre-created dir + our marker persist.
            if let Some(parent) = std::path::Path::new(&path).parent() {
                std::fs::create_dir_all(parent).with_context(|| {
                    format!("create bridge-DNS marker dir {}", parent.display())
                })?;
            }
            std::fs::write(&path, format!("{}\n", iso.gateway_ip))
                .with_context(|| format!("write bridge-DNS marker {path}"))?;
        }
        None => match std::fs::remove_file(&path) {
            Ok(()) => {}
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
            Err(e) => return Err(e).with_context(|| format!("remove bridge-DNS marker {path}")),
        },
    }
    Ok(())
}

/// `SyncAgentTmpfiles` — write `/etc/tmpfiles.d/hyperhive-agents.conf` for
/// the given agent set and immediately apply it with `systemd-tmpfiles --create`.
///
/// Each call atomically replaces the file with entries for all current agents,
/// then creates any missing dirs on the running host. The file survives reboots
/// and is read by `systemd-tmpfiles-setup.service` (runs in `sysinit.target`,
/// before any container units can start), so bind-mount source dirs are always
/// pre-created regardless of whether hive-c0re has reached `ensure_agent_runtime_dir`.
///
/// Directories written per agent:
/// - `/run/hyperhive/agents/<name>` (MCP socket dir, bind-mounted into container
///   as `/run/hive`)
/// - `/run/hive-agent/<name>` (web socket dir, bind-mounted into container)
const TMPFILES_PATH: &str = "/etc/tmpfiles.d/hyperhive-agents.conf";

async fn sync_agent_tmpfiles(agents: &[AgentTmpfilesEntry]) -> Result<(String, String)> {
    use std::fmt::Write as _;
    for entry in agents {
        validate_agent_name(&entry.name)?;
    }

    // Build tmpfiles.d content. Root dirs first, then per-agent.
    let mut content =
        String::from("# managed by hive-c0re — do not edit (regenerated on spawn/destroy)\n");
    // Parent dirs — created with permissive mode so hive-c0re can make subdirs.
    // /run/hyperhive itself is also a RuntimeDirectory of hive-c0re.service; the
    // tmpfiles.d entry here ensures it exists before hive-c0re starts (boot race).
    content.push_str("d /run/hyperhive 0750 hive-core hive-core -\n");
    writeln!(content, "d {AGENT_RUNTIME_ROOT} 0755 hive-core hive-core -").ok();
    // `hive-core`, not root: c0re does the `create_dir_all` for a new agent's
    // subdir itself, so a root-owned parent EACCESes on the first spawn of a
    // fresh host. This must stay in step with the identical rule in
    // `nix/host-modules/hive-gateway/default.nix` — the two files declared
    // different owners for this one path, and which won depended on the order
    // systemd happened to read them in.
    writeln!(content, "d {SOCKET_DIR_ROOT} 0755 hive-core hive-core -").ok();
    // Per-agent dirs.
    for entry in agents {
        let name = &entry.name;
        writeln!(
            content,
            "d {AGENT_RUNTIME_ROOT}/{name} 0755 hive-core hive-core -"
        )
        .ok();
        // The agent's socket dir. Three principals need it and no two share a
        // group, so the mode has to say so explicitly:
        //
        //   owner = the agent user   rwx  binds + unlinks agent.sock/web.sock
        //   other =                  --x  traverse only, no listing
        //
        // "other" covers hive-c0re (dials agent.sock) and the gateway's nginx
        // (dials web.sock, and has all of /run/hive-agent bind-mounted in).
        // Both sockets are 0666, so traversal is all they need.
        //
        // 0751 rather than the historical 0777 is a fix, not a tidy-up:
        // write permission on a *directory* is what confers the right to
        // unlink its entries, whoever owns them — the sticky bit is the only
        // thing that would restrain that, and it was never set here. So the
        // old world-writable mode let anything able to reach the path delete
        // an agent's socket, bind its own, and receive that agent's todos.
        // Dropping `o=w` removes that permission outright rather than
        // qualifying it. Declaring the owner here also ends the tug-of-war
        // with the
        // old ChownSocketDir: `d` re-applies on every sync, so a chown made
        // afterwards was reset by the next agent's spawn.
        if let (Some(uid), Some(gid)) = (entry.uid, entry.gid) {
            writeln!(content, "d {SOCKET_DIR_ROOT}/{name} 0751 {uid} {gid} -").ok();
        } else {
            // Before the container's /etc/passwd exists there is no uid to
            // name, and the harness must still be able to bind. Keep the old
            // permissive mode for that agent alone; the next sync (any spawn
            // or destroy, or c0re restart) resolves the uid and tightens it.
            tracing::info!(%name, "tmpfiles.d: agent uid unknown, deferring 0751 on socket dir");
            writeln!(content, "d {SOCKET_DIR_ROOT}/{name} 0777 root root -").ok();
        }
    }

    // Atomic write: write to a tmp file then rename so a concurrent reader
    // always sees a complete file.
    let tmp = format!("{TMPFILES_PATH}.tmp");
    std::fs::write(&tmp, &content).with_context(|| format!("write {tmp}"))?;
    std::fs::rename(&tmp, TMPFILES_PATH)
        .with_context(|| format!("rename {TMPFILES_PATH}.tmp -> {TMPFILES_PATH}"))?;
    tracing::info!(agents = agents.len(), "tmpfiles.d: wrote {TMPFILES_PATH}");

    // Apply immediately so dirs exist on the running host, not just after next boot.
    let out = Command::new("systemd-tmpfiles")
        .args(["--create", TMPFILES_PATH])
        .output()
        .await
        .context("systemd-tmpfiles --create")?;
    if !out.status.success() {
        let stderr = String::from_utf8_lossy(&out.stderr).trim().to_owned();
        anyhow::bail!(
            "systemd-tmpfiles --create failed ({}): {stderr}",
            out.status
        );
    }
    Ok((String::new(), String::new()))
}

#[cfg(test)]
mod tests {
    use super::{
        BindMount, OwnedFd, PAUSED_MARKER_FILE, PrivRequest, check_fd_agreement,
        clear_runner_credentials, contains_secret_shaped_run, git_overlay_flags,
        limits_dropin_body, redact_secret_line, remove_marker_in, toplevel_attr,
        write_state_file_nofollow,
    };
    use std::path::PathBuf;
    use std::sync::atomic::{AtomicU32, Ordering};

    fn bind(container_path: &str) -> BindMount {
        BindMount {
            host_path: "/var/lib/hyperhive/whatever".to_owned(),
            container_path: container_path.to_owned(),
            read_only: true,
        }
    }

    /// Pins the exact attr path we hand to `nix build` — it has to match
    /// `hive-c0re`'s own `lifecycle::prebuild_toplevel` construction, since
    /// that step's whole point is warming the store for this later build.
    /// A drifted attr path defeats the cache-warming silently — no error,
    /// just a slower `update`.
    #[test]
    fn toplevel_attr_matches_prebuild_toplevels_construction() {
        assert_eq!(
            toplevel_attr("atlas"),
            "/var/lib/hyperhive/meta#nixosConfigurations.atlas.config.system.build.toplevel"
        );
    }

    /// Every bound git repo gets its `.git` overlaid — the knowledge tree
    /// and *each* config mount, an agent's own plus every child's.
    ///
    /// The child case is the one worth pinning: that set grows at runtime
    /// as agents gain children, so a rule written as a list of names would
    /// silently stop covering new ones.
    #[test]
    fn every_bound_git_repo_gets_its_dot_git_hidden() {
        let flags = git_overlay_flags(&[
            bind("/knowledge"),
            bind("/agents/atlas/config"),
            bind("/agents/kiddo/config"),
        ]);
        assert_eq!(
            flags,
            [
                "--tmpfs=/knowledge/.git",
                "--tmpfs=/agents/atlas/config/.git",
                "--tmpfs=/agents/kiddo/config/.git",
            ]
        );
    }

    /// ...and nothing else does. A blanket "overlay .git on every bind"
    /// would mask a real `.git` under `state/`, where an agent legitimately
    /// keeps working clones of its own.
    #[test]
    fn non_repo_mounts_are_left_alone() {
        let flags = git_overlay_flags(&[
            bind("/agents/atlas/state"),
            bind("/shared"),
            bind("/applied"),
            bind("/agents/atlas/config-notes"),
        ]);
        assert!(flags.is_empty(), "overlaid a non-repo mount: {flags:?}");
    }

    /// A request that streams into a caller-supplied descriptor.
    fn fd_taking_request() -> PrivRequest {
        PrivRequest::SendAgentSnapshotToFd {
            agent_name: "atlas".to_owned(),
            snapshot_name: "hive-migrate".to_owned(),
            parent_snapshot_name: None,
        }
    }

    /// A real descriptor — `/dev/null` rather than a fake, so the drop
    /// that closes it on a rejection path is genuinely exercised.
    fn some_fd() -> OwnedFd {
        std::fs::File::open("/dev/null")
            .expect("open /dev/null")
            .into()
    }

    /// An op that streams into a passed descriptor cannot invent one:
    /// falling back to anything (a temp file, the response socket) would
    /// send an agent's state somewhere the caller never asked for.
    #[test]
    fn an_fd_taking_op_without_a_descriptor_is_rejected() {
        let err = check_fd_agreement(&fd_taking_request(), None)
            .expect_err("no descriptor arrived, so this must not proceed");
        let msg = format!("{err:#}");
        assert!(msg.contains("requires a passed file descriptor"), "{msg}");
    }

    /// The mirror case: a descriptor sent alongside an op that takes
    /// none is a protocol error, not something to ignore. Returning the
    /// error drops the `OwnedFd`, which closes it — the alternative
    /// leaks one descriptor per stray request in a long-lived root
    /// process.
    #[test]
    fn a_descriptor_sent_to_an_op_that_takes_none_is_rejected() {
        let fd = some_fd();
        let err = check_fd_agreement(&PrivRequest::DaemonReload, Some(&fd))
            .expect_err("an unexpected descriptor must not be silently ignored");
        let msg = format!("{err:#}");
        assert!(
            msg.contains("does not take a passed file descriptor"),
            "{msg}"
        );
    }

    /// Both agreeing combinations pass, so the check rejects mismatches
    /// rather than descriptors in general.
    #[test]
    fn agreeing_combinations_are_accepted() {
        let fd = some_fd();
        check_fd_agreement(&fd_taking_request(), Some(&fd))
            .expect("an fd-taking op with its descriptor is the normal case");
        check_fd_agreement(&PrivRequest::DaemonReload, None)
            .expect("every ordinary request arrives without a descriptor");
    }

    /// The whole rendered body, pinned literally — including the values,
    /// so changing the restart policy is a visible test edit rather than a
    /// silent one.
    ///
    /// Placement is the part most worth pinning: `StartLimit*` are `[Unit]`
    /// settings and systemd **silently ignores** them under `[Service]`, so
    /// a bound that moved sections would look configured and do nothing.
    /// An unset weight still emits no line at all, which is what keeps a
    /// hive-c0re older than that field from changing what lands on disk.
    #[test]
    fn dropin_body_is_pinned_exactly() {
        assert_eq!(
            limits_dropin_body("/run/hyperhive/agents/iris", "4G", "200%", None, None),
            "[Unit]\n\
             ConditionPathIsDirectory=/run/hyperhive/agents/iris\n\
             StartLimitIntervalSec=600\n\
             StartLimitBurst=3\n\
             \n\
             [Service]\n\
             RestartSec=5\n\
             MemoryMax=4G\n\
             CPUQuota=200%\n"
        );
    }

    /// The bound is hive-wide **policy**, not a per-agent parameter: it is
    /// rendered from constants and no caller-supplied value can omit or
    /// alter it. This is the property that justifies keeping it out of the
    /// wire protocol — if it ever varies by request, that argument is gone.
    #[test]
    fn the_start_limit_is_present_whatever_the_caller_passes() {
        for (mem, cpu, cw, iw) in [
            ("4G", "200%", None, None),
            ("512M", "50%", Some(10), Some(10)),
            ("infinity", "infinity", Some(10_000), None),
        ] {
            let body = limits_dropin_body("/rt/x", mem, cpu, cw, iw);
            let unit = body
                .split("[Service]")
                .next()
                .expect("the body always has a [Unit] section before [Service]");
            assert!(
                unit.contains("StartLimitIntervalSec=600") && unit.contains("StartLimitBurst=3"),
                "start limit missing from [Unit] for ({mem}, {cpu}): {body}"
            );
            assert!(
                body.contains("\nRestartSec=5\n"),
                "restart backoff missing for ({mem}, {cpu}): {body}"
            );
        }
    }

    /// Weights are appended to the `[Service]` section, each omitted
    /// independently when `None`.
    #[test]
    fn weights_are_emitted_only_when_set() {
        let both = limits_dropin_body("/rt/x", "4G", "200%", Some(80), Some(80));
        assert!(
            both.ends_with("CPUQuota=200%\nCPUWeight=80\nIOWeight=80\n"),
            "{both}"
        );

        let cpu_only = limits_dropin_body("/rt/x", "4G", "200%", Some(80), None);
        assert!(
            cpu_only.ends_with("CPUQuota=200%\nCPUWeight=80\n"),
            "{cpu_only}"
        );
        assert!(!cpu_only.contains("IOWeight"), "{cpu_only}");

        let io_only = limits_dropin_body("/rt/x", "4G", "200%", None, Some(80));
        assert!(
            io_only.ends_with("CPUQuota=200%\nIOWeight=80\n"),
            "{io_only}"
        );
        assert!(!io_only.contains("CPUWeight"), "{io_only}");
    }

    #[test]
    fn redacts_lines_mentioning_password_case_insensitively() {
        assert_eq!(
            redact_secret_line("New password: hunter2"),
            "[redacted: line mentions a password]"
        );
        assert_eq!(
            redact_secret_line("PASSWORD=hunter2"),
            "[redacted: line mentions a password]"
        );
        assert_eq!(
            redact_secret_line("User \"foo\" was successfully created."),
            "User \"foo\" was successfully created."
        );
    }

    /// The regression this function exists for. The keyword rule passes
    /// this line straight through — it says nothing about a password — so
    /// only the shape rule catches it.
    #[test]
    fn redacts_access_token_line_which_mentions_no_password() {
        let line =
            "Access token was successfully created: 0123456789abcdef0123456789abcdef01234567";
        assert!(
            !line.to_ascii_lowercase().contains("password"),
            "fixture must not contain the keyword, or it proves nothing"
        );
        assert_eq!(
            redact_secret_line(line),
            "[redacted: line contains a secret-shaped token]"
        );
    }

    #[test]
    fn secret_shape_boundaries() {
        // Ordinary forgejo-admin output survives: no run is long enough.
        assert_eq!(
            redact_secret_line("Command 'user' 'create' finished with no errors."),
            "Command 'user' 'create' finished with no errors."
        );
        // 31 chars is below the floor, 32 is at it.
        assert!(!contains_secret_shaped_run(&"a".repeat(31)));
        assert!(contains_secret_shaped_run(&"a".repeat(32)));
        // Punctuation breaks the run — a sentence never trips it however long.
        assert!(!contains_secret_shaped_run(
            "this.is.a.very.long.dotted.identifier.but.not.a.secret"
        ));
        // base64url and hex alphabets both count.
        assert!(contains_secret_shaped_run(
            "ZGVhZGJlZWZkZWFkYmVlZmRlYWRiZWVmZGVhZA=="
        ));
        assert!(contains_secret_shaped_run(
            "aG93-dy_there-aG93dy1theresomething"
        ));
    }

    /// argus on the review: a whitespace-delimited check is defeated by
    /// punctuation glued to the secret — the punctuation joins the "word"
    /// and fails the alphabet test for the whole run, while the credential
    /// sits there in full. Scanning for a RUN rather than a WORD closes it.
    /// These are the shapes that used to slip through.
    #[test]
    fn secret_is_caught_with_punctuation_glued_to_it() {
        const TOK: &str = "0123456789abcdef0123456789abcdef01234567";
        for line in [
            format!("token: {TOK},"),
            format!("token: {TOK}."),
            format!("using [{TOK}] now"),
            format!("value=\"{TOK}\""),
            format!("(created {TOK})"),
            // no whitespace anywhere -- one glued blob
            format!("Bearer:{TOK};next"),
        ] {
            assert_eq!(
                redact_secret_line(&line),
                "[redacted: line contains a secret-shaped token]",
                "leaked through: {line}"
            );
        }
    }

    /// Unique scratch dir per test, no external tempfile dep.
    fn scratch() -> PathBuf {
        static CTR: AtomicU32 = AtomicU32::new(0);
        let n = CTR.fetch_add(1, Ordering::Relaxed);
        let dir = std::env::temp_dir().join(format!(
            "hive-priv-nofollow-test-{}-{n}",
            std::process::id()
        ));
        std::fs::create_dir_all(&dir).unwrap();
        dir
    }

    #[test]
    fn rejects_non_plain_filenames() {
        let dir = scratch();
        for bad in ["", ".", "..", "a/b", "/etc/passwd", "../escape", "sub/tok"] {
            assert!(
                write_state_file_nofollow(&dir, bad, "x").is_err(),
                "must reject filename {bad:?}"
            );
        }
        std::fs::remove_dir_all(&dir).ok();
    }

    #[test]
    fn refuses_symlink_leaf_and_leaves_target_untouched() {
        let dir = scratch();
        let target = dir.join("target");
        std::fs::write(&target, "original").unwrap();
        // Agent plants a symlink where the token would be written.
        std::os::unix::fs::symlink(&target, dir.join("forge-token")).unwrap();

        let res = write_state_file_nofollow(&dir, "forge-token", "PWNED");
        assert!(res.is_err(), "O_NOFOLLOW must refuse a symlink leaf");
        // The root-privileged write must NOT have followed the link.
        assert_eq!(
            std::fs::read_to_string(&target).unwrap(),
            "original",
            "symlink target must be untouched"
        );
        std::fs::remove_dir_all(&dir).ok();
    }

    #[test]
    fn writes_plain_file_0600() {
        use std::os::unix::fs::PermissionsExt as _;
        let dir = scratch();
        write_state_file_nofollow(&dir, "forge-token", "secret").unwrap();
        let path = dir.join("forge-token");
        assert_eq!(std::fs::read_to_string(&path).unwrap(), "secret");
        let mode = std::fs::metadata(&path).unwrap().permissions().mode() & 0o777;
        assert_eq!(mode, 0o600, "token file must be 0600");
        // Overwrite truncates cleanly (O_TRUNC), no residue.
        write_state_file_nofollow(&dir, "forge-token", "new").unwrap();
        assert_eq!(std::fs::read_to_string(&path).unwrap(), "new");
        std::fs::remove_dir_all(&dir).ok();
    }

    /// The runner-credential clear, in all three states that matter. The
    /// PRESENCE arm is the load-bearing one: an implementation that did nothing
    /// at all would pass the "absent is fine" arm perfectly, and the whole point
    /// of the call is that the file is *gone* afterwards — upstream re-registers
    /// on absence and on nothing else we control.
    #[test]
    fn clearing_runner_credentials_removes_it_and_tolerates_absence() {
        let dir = scratch();
        let path = dir.join(".runner");
        let path_str = path.to_str().unwrap();

        // Absent → success (this is the state we are aiming for).
        assert!(!path.exists());
        clear_runner_credentials(path_str).unwrap();

        // Present → success AND actually gone. Without this arm a no-op passes.
        std::fs::write(&path, r#"{"id":7,"address":"http://old.invalid"}"#).unwrap();
        assert!(
            path.exists(),
            "control: the file must exist before the clear"
        );
        clear_runner_credentials(path_str).unwrap();
        assert!(
            !path.exists(),
            "stale credentials must be GONE, or the restart takes upstream's \
             already-registered branch and registration silently never happens"
        );

        std::fs::remove_dir_all(&dir).ok();
    }

    /// A failure that is not `NotFound` must propagate, never read as success.
    /// A directory in the file's place makes `remove_file` fail with a non-
    /// `NotFound` error without needing to drop privileges in a test.
    #[test]
    fn clearing_runner_credentials_propagates_a_real_failure() {
        let dir = scratch();
        let path = dir.join(".runner");
        std::fs::create_dir(&path).unwrap();

        let err = clear_runner_credentials(path.to_str().unwrap())
            .expect_err("a non-NotFound failure must NOT be reported as success");
        assert!(
            format!("{err:#}").contains("remove stale runner credentials"),
            "error must name what it failed to do, got: {err:#}"
        );
        assert!(
            path.exists(),
            "nothing was removed, and the caller must know"
        );

        std::fs::remove_dir_all(&dir).ok();
    }

    /// The pause marker round-trips through the same root-only path the
    /// credential writes use, and BOTH directions are idempotent — the
    /// dashboard toggle and `hivectl pause|resume` fire blind, without
    /// reading the current state first.
    #[test]
    fn pause_marker_create_and_remove_are_idempotent() {
        let dir = scratch();
        let path = dir.join(PAUSED_MARKER_FILE);

        for _ in 0..2 {
            write_state_file_nofollow(&dir, PAUSED_MARKER_FILE, "").unwrap();
            assert!(path.exists(), "marker must exist after pause");
            assert_eq!(std::fs::read_to_string(&path).unwrap(), "");
        }
        for _ in 0..2 {
            remove_marker_in(&dir, PAUSED_MARKER_FILE).unwrap();
            assert!(!path.exists(), "marker must be gone after resume");
        }
        std::fs::remove_dir_all(&dir).ok();
    }

    /// A resume must never follow an agent-planted symlink at the marker
    /// path: this unlink runs as root, so following it would let an agent
    /// delete an arbitrary file on the host.
    #[test]
    fn resume_unlinks_the_symlink_not_its_target() {
        let dir = scratch();
        let target = dir.join("target");
        std::fs::write(&target, "original").unwrap();
        let link = dir.join(PAUSED_MARKER_FILE);
        std::os::unix::fs::symlink(&target, &link).unwrap();

        remove_marker_in(&dir, PAUSED_MARKER_FILE).unwrap();
        // `exists()` follows the link, so it can't tell "link removed" from
        // "target removed, dangling link left" — stat the link itself.
        assert!(
            std::fs::symlink_metadata(&link).is_err(),
            "the link itself must be unlinked"
        );
        assert_eq!(
            std::fs::read_to_string(&target).unwrap(),
            "original",
            "symlink target must survive the root unlink"
        );
        std::fs::remove_dir_all(&dir).ok();
    }
}