harn_vm/

harness.rs

//! Capability handle threaded into every Harn script as the `harness`
//! parameter of `main`.
//!
//! `Harness` is the Harn-language analog of an explicit-capability handle: a
//! single value the runtime hands to a script's `main` so that stdio, clock,
//! filesystem, environment, randomness, and network access become surface in
//! the type system instead of ambient globals. Each sub-handle (`stdio`,
//! `clock`, `fs`, `env`, `random`, `net`) is a distinct named type that
//! anchors the surface for its capability slice.
//!
//! This module defines:
//!   * The runtime [`Harness`] value (and six sub-handle wrappers).
//!   * [`Harness::real`], the production constructor that wraps wall-clock
//!     time, `tokio::fs`, `std::env`, `rand::thread_rng`, and `reqwest`. The
//!     downstream migration tickets (E4.2-E4.4) populate the per-handle
//!     method surface against this concrete state; the E4.2 stdio surface is
//!     wired while filesystem, environment, randomness, and network methods
//!     still land in later slices.
//!   * [`VmHarness`], the compact `VmValue` payload that carries the same
//!     state through the bytecode VM and distinguishes the root handle from
//!     its sub-handles via [`HarnessKind`].

use std::collections::{BTreeMap, VecDeque};
use std::fmt;
use std::rc::Rc;
use std::sync::{Arc, Mutex};
use std::time::Duration;

use async_trait::async_trait;
use harn_clock::{Clock, PausedClock, RealClock};
use time::OffsetDateTime;

/// Six capability slices exposed by a [`Harness`].
///
/// `Root` is the parent handle; the others are the typed sub-handles users
/// reach through field access (`harness.stdio`, `harness.clock`, ...).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum HarnessKind {
    Root,
    Stdio,
    Clock,
    Fs,
    Env,
    Random,
    Net,
}

impl HarnessKind {
    /// The Harn-language type name for this kind (`Harness`, `HarnessStdio`,
    /// etc.). Used by the typechecker primitive registration and by
    /// `VmValue::type_name`.
    pub const fn type_name(self) -> &'static str {
        match self {
            HarnessKind::Root => "Harness",
            HarnessKind::Stdio => "HarnessStdio",
            HarnessKind::Clock => "HarnessClock",
            HarnessKind::Fs => "HarnessFs",
            HarnessKind::Env => "HarnessEnv",
            HarnessKind::Random => "HarnessRandom",
            HarnessKind::Net => "HarnessNet",
        }
    }

    /// Field name a parent `Harness` exposes for this sub-handle (e.g. the
    /// `stdio` in `harness.stdio`). Returns `None` for the root.
    pub const fn field_name(self) -> Option<&'static str> {
        match self {
            HarnessKind::Root => None,
            HarnessKind::Stdio => Some("stdio"),
            HarnessKind::Clock => Some("clock"),
            HarnessKind::Fs => Some("fs"),
            HarnessKind::Env => Some("env"),
            HarnessKind::Random => Some("random"),
            HarnessKind::Net => Some("net"),
        }
    }

    /// Parse the field name a script uses to reach a sub-handle.
    pub fn from_field_name(name: &str) -> Option<Self> {
        match name {
            "stdio" => Some(HarnessKind::Stdio),
            "clock" => Some(HarnessKind::Clock),
            "fs" => Some(HarnessKind::Fs),
            "env" => Some(HarnessKind::Env),
            "random" => Some(HarnessKind::Random),
            "net" => Some(HarnessKind::Net),
            _ => None,
        }
    }

    /// All six sub-handle kinds, in the canonical field order.
    pub const SUB_HANDLES: &'static [HarnessKind] = &[
        HarnessKind::Stdio,
        HarnessKind::Clock,
        HarnessKind::Fs,
        HarnessKind::Env,
        HarnessKind::Random,
        HarnessKind::Net,
    ];

    /// Every kind a Harn-script type annotation may reference.
    pub const ALL: &'static [HarnessKind] = &[
        HarnessKind::Root,
        HarnessKind::Stdio,
        HarnessKind::Clock,
        HarnessKind::Fs,
        HarnessKind::Env,
        HarnessKind::Random,
        HarnessKind::Net,
    ];
}

/// Shared, refcounted state backing every sub-handle of a single `Harness`.
///
/// Method implementations (in `crate::vm::methods::harness`) borrow this to
/// reach the concrete OS-backed primitives. Wrapped in `Arc` so handles are
/// `Send + Sync` for VM contexts that move work onto other tasks.
#[derive(Debug)]
pub struct HarnessInner {
    clock: Arc<dyn Clock>,
    mode: HarnessMode,
}

impl HarnessInner {
    pub fn clock(&self) -> &Arc<dyn Clock> {
        &self.clock
    }

    pub(crate) fn mode(&self) -> &HarnessMode {
        &self.mode
    }
}

#[derive(Debug)]
pub(crate) enum HarnessMode {
    Real,
    Null(NullHarnessState),
    Mock(Box<MockHarnessState>),
}

#[derive(Debug, Default)]
pub(crate) struct NullHarnessState {
    deny_events: Mutex<Vec<DenyEvent>>,
}

impl NullHarnessState {
    pub(crate) fn record_deny(
        &self,
        sub_handle: HarnessKind,
        method: &str,
        args: &[crate::VmValue],
    ) {
        self.deny_events
            .lock()
            .expect("deny events poisoned")
            .push(DenyEvent::new(
                sub_handle,
                method,
                args.iter().map(crate::VmValue::display).collect(),
            ));
    }

    pub(crate) fn deny_events(&self) -> Vec<DenyEvent> {
        self.deny_events
            .lock()
            .expect("deny events poisoned")
            .clone()
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DenyEvent {
    pub sub_handle: HarnessKind,
    pub method: String,
    pub args: Vec<String>,
}

impl DenyEvent {
    fn new(sub_handle: HarnessKind, method: &str, args: Vec<String>) -> Self {
        Self {
            sub_handle,
            method: method.to_string(),
            args,
        }
    }
}

#[derive(Debug)]
pub(crate) struct MockHarnessState {
    calls: Mutex<Vec<HarnessCall>>,
    clock: Arc<PausedClock>,
    env: BTreeMap<String, String>,
    fs_reads: BTreeMap<String, Vec<u8>>,
    net_gets: BTreeMap<String, String>,
    random_u64: Mutex<VecDeque<u64>>,
    stdin_lines: Mutex<VecDeque<String>>,
    stdio: Mutex<String>,
    stderr: Mutex<String>,
}

impl MockHarnessState {
    pub(crate) fn record_call(
        &self,
        sub_handle: HarnessKind,
        method: &str,
        args: &[crate::VmValue],
    ) {
        self.calls
            .lock()
            .expect("calls poisoned")
            .push(HarnessCall::new(
                sub_handle,
                method,
                args.iter().map(crate::VmValue::display).collect(),
            ));
    }

    pub(crate) fn calls(&self) -> Vec<HarnessCall> {
        self.calls.lock().expect("calls poisoned").clone()
    }

    pub(crate) fn env_get(&self, key: &str) -> Option<&str> {
        self.env.get(key).map(String::as_str)
    }

    pub(crate) fn fs_read(&self, path: &str) -> Option<&[u8]> {
        self.fs_reads.get(path).map(Vec::as_slice)
    }

    pub(crate) fn net_get(&self, url: &str) -> Option<&str> {
        self.net_gets.get(url).map(String::as_str)
    }

    pub(crate) fn next_random_u64(&self) -> Option<u64> {
        let mut values = self.random_u64.lock().expect("random values poisoned");
        values.pop_front()
    }

    pub(crate) fn advance_clock(&self, duration: std::time::Duration) {
        self.clock.advance(duration);
    }

    pub(crate) fn push_stdio(&self, text: &str) {
        self.stdio
            .lock()
            .expect("stdio buffer poisoned")
            .push_str(text);
    }

    pub(crate) fn stdio(&self) -> String {
        self.stdio.lock().expect("stdio buffer poisoned").clone()
    }

    pub(crate) fn push_stderr(&self, text: &str) {
        self.stderr
            .lock()
            .expect("stderr buffer poisoned")
            .push_str(text);
    }

    pub(crate) fn stderr(&self) -> String {
        self.stderr.lock().expect("stderr buffer poisoned").clone()
    }

    pub(crate) fn pop_stdin_line(&self) -> Option<String> {
        self.stdin_lines
            .lock()
            .expect("stdin queue poisoned")
            .pop_front()
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct HarnessCall {
    pub sub_handle: HarnessKind,
    pub method: String,
    pub args: Vec<String>,
}

impl HarnessCall {
    fn new(sub_handle: HarnessKind, method: &str, args: Vec<String>) -> Self {
        Self {
            sub_handle,
            method: method.to_string(),
            args,
        }
    }
}

#[derive(Debug)]
pub struct MockHarnessBuilder {
    clock: Arc<PausedClock>,
    env: BTreeMap<String, String>,
    fs_reads: BTreeMap<String, Vec<u8>>,
    net_gets: BTreeMap<String, String>,
    random_u64: Vec<u64>,
    stdin_lines: Vec<String>,
}

impl MockHarnessBuilder {
    fn new() -> Self {
        Self {
            clock: paused_clock_at_unix_ms(0),
            env: BTreeMap::new(),
            fs_reads: BTreeMap::new(),
            net_gets: BTreeMap::new(),
            random_u64: Vec::new(),
            stdin_lines: Vec::new(),
        }
    }

    pub fn clock_at_unix_ms(mut self, unix_ms: i64) -> Self {
        self.clock = paused_clock_at_unix_ms(unix_ms);
        self
    }

    pub fn clock_at(mut self, origin: OffsetDateTime) -> Self {
        self.clock = PausedClock::new(origin);
        self
    }

    pub fn env(mut self, key: impl Into<String>, value: impl Into<String>) -> Self {
        self.env.insert(key.into(), value.into());
        self
    }

    pub fn fs_read(mut self, path: impl Into<String>, data: impl Into<Vec<u8>>) -> Self {
        self.fs_reads.insert(path.into(), data.into());
        self
    }

    pub fn net_get(mut self, url: impl Into<String>, body: impl Into<String>) -> Self {
        self.net_gets.insert(url.into(), body.into());
        self
    }

    pub fn random_u64(mut self, value: u64) -> Self {
        self.random_u64.push(value);
        self
    }

    /// Queue a line that `harness.stdio.read_line()` or
    /// `harness.stdio.prompt(...)` will return next. Lines are dequeued
    /// FIFO; once the queue is empty subsequent reads surface EOF
    /// (`nil` for the unstructured form, `{ok: false, status: "eof"}`
    /// for the structured form).
    pub fn stdin_line(mut self, line: impl Into<String>) -> Self {
        self.stdin_lines.push(line.into());
        self
    }

    pub fn build(self) -> Harness {
        let clock = self.clock;
        Harness::with_mode(
            clock.clone() as Arc<dyn Clock>,
            HarnessMode::Mock(Box::new(MockHarnessState {
                calls: Mutex::new(Vec::new()),
                clock,
                env: self.env,
                fs_reads: self.fs_reads,
                net_gets: self.net_gets,
                random_u64: Mutex::new(self.random_u64.into()),
                stdin_lines: Mutex::new(self.stdin_lines.into()),
                stdio: Mutex::new(String::new()),
                stderr: Mutex::new(String::new()),
            })),
        )
    }
}

/// The runtime handle threaded into `main(harness: Harness)`.
///
/// Cheap to clone; sub-handles share the same `Arc` inner state.
#[derive(Debug, Clone)]
pub struct Harness {
    inner: Arc<HarnessInner>,
}

impl Harness {
    /// Build the production handle wired to wall-clock time. Filesystem,
    /// environment, randomness, and network access are layered on by the
    /// E4.2-E4.4 migration tickets; the constructor only needs to succeed
    /// without panicking today (per the E4.1 exit criteria).
    ///
    /// The production clock is wrapped in [`MockAwareClock`] so existing
    /// `mock_time(...)` / `advance_time(...)` test fixtures observe
    /// `harness.clock.*` reads identically to the ambient builtins. The
    /// shim is part of the E4.3-E4.6 migration window and goes away once
    /// the ambient `mock_time` test utility is retired by E4.5.
    pub fn real() -> Self {
        Self::with_mode(
            Arc::new(MockAwareClock::new(RealClock::new())),
            HarnessMode::Real,
        )
    }

    /// Build a deny-by-default test handle. Every sub-handle method records a
    /// [`DenyEvent`] and fails with a categorized VM error.
    pub fn null() -> Self {
        Self::with_mode(
            paused_clock_at_unix_ms(0) as Arc<dyn Clock>,
            HarnessMode::Null(NullHarnessState::default()),
        )
    }

    /// Build a record/replay test handle backed by a paused clock.
    pub fn mock() -> MockHarnessBuilder {
        MockHarnessBuilder::new()
    }

    /// Build a handle wired to a caller-supplied clock. Most callers want
    /// [`Self::test`] (which constructs the `PausedClock` for you);
    /// reach for this when an existing `Arc<dyn Clock>` is already in
    /// hand — e.g. a `RecordedClock` wrapper.
    pub fn with_clock(clock: Arc<dyn Clock>) -> Self {
        Self::with_mode(clock, HarnessMode::Real)
    }

    fn with_mode(clock: Arc<dyn Clock>, mode: HarnessMode) -> Self {
        Self {
            inner: Arc::new(HarnessInner { clock, mode }),
        }
    }

    pub fn deny_events(&self) -> Vec<DenyEvent> {
        match self.inner.mode() {
            HarnessMode::Null(state) => state.deny_events(),
            HarnessMode::Real | HarnessMode::Mock(_) => Vec::new(),
        }
    }

    pub fn calls(&self) -> Vec<HarnessCall> {
        match self.inner.mode() {
            HarnessMode::Mock(state) => state.calls(),
            HarnessMode::Real | HarnessMode::Null(_) => Vec::new(),
        }
    }

    pub fn captured_stdio(&self) -> String {
        match self.inner.mode() {
            HarnessMode::Mock(state) => state.stdio(),
            HarnessMode::Real | HarnessMode::Null(_) => String::new(),
        }
    }

    pub fn captured_stderr(&self) -> String {
        match self.inner.mode() {
            HarnessMode::Mock(state) => state.stderr(),
            HarnessMode::Real | HarnessMode::Null(_) => String::new(),
        }
    }

    /// Build a deterministic test handle wired to a fresh
    /// [`PausedClock`] pinned at the Unix epoch.
    ///
    /// Returns the harness paired with the underlying `PausedClock` so
    /// tests can drive virtual time through `PausedClock::advance`
    /// while passing the same `Harness` value into the VM. The two
    /// share the underlying `Arc<dyn Clock>`, so the harness reflects
    /// every advance immediately.
    ///
    /// Pairs with [`PausedClock::advance`] / [`PausedClock::set`] — see
    /// [`Self::with_paused_clock`] for picking a non-epoch origin.
    pub fn test() -> (Self, Arc<PausedClock>) {
        Self::with_paused_clock(OffsetDateTime::UNIX_EPOCH)
    }

    /// Like [`Self::test`], but pins the paused clock's wall origin to
    /// `origin`. Lets tests anchor virtual time to a meaningful date
    /// without manually advancing past the epoch first.
    pub fn with_paused_clock(origin: OffsetDateTime) -> (Self, Arc<PausedClock>) {
        let paused = PausedClock::new(origin);
        let as_dyn: Arc<dyn Clock> = paused.clone();
        (Self::with_clock(as_dyn), paused)
    }

    /// Field access for `harness.stdio`.
    pub fn stdio(&self) -> HarnessStdio {
        HarnessStdio {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Field access for `harness.clock`.
    pub fn clock(&self) -> HarnessClock {
        HarnessClock {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Field access for `harness.fs`.
    pub fn fs(&self) -> HarnessFs {
        HarnessFs {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Field access for `harness.env`.
    pub fn env(&self) -> HarnessEnv {
        HarnessEnv {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Field access for `harness.random`.
    pub fn random(&self) -> HarnessRandom {
        HarnessRandom {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Field access for `harness.net`.
    pub fn net(&self) -> HarnessNet {
        HarnessNet {
            inner: Arc::clone(&self.inner),
        }
    }

    /// Lower this handle into the `VmValue::Harness` payload.
    pub fn into_vm_value(self) -> crate::value::VmValue {
        crate::value::VmValue::Harness(VmHarness {
            inner: self.inner,
            kind: HarnessKind::Root,
        })
    }
}

fn paused_clock_at_unix_ms(unix_ms: i64) -> Arc<PausedClock> {
    let nanos = (unix_ms as i128).saturating_mul(1_000_000);
    let origin =
        OffsetDateTime::from_unix_timestamp_nanos(nanos).unwrap_or(OffsetDateTime::UNIX_EPOCH);
    PausedClock::new(origin)
}

pub(crate) fn vm_string(value: impl Into<String>) -> crate::VmValue {
    crate::VmValue::String(Rc::from(value.into()))
}

impl Default for Harness {
    fn default() -> Self {
        Self::real()
    }
}

/// stdio sub-handle: `print`, `println`, `eprint`, `eprintln`, `prompt`,
/// `read_line`.
#[derive(Debug, Clone)]
pub struct HarnessStdio {
    inner: Arc<HarnessInner>,
}

/// clock sub-handle: `now`, `monotonic_now`, `sleep`.
#[derive(Debug, Clone)]
pub struct HarnessClock {
    inner: Arc<HarnessInner>,
}

impl HarnessClock {
    pub fn clock(&self) -> &Arc<dyn Clock> {
        self.inner.clock()
    }
}

/// fs sub-handle: `read_file`, `write_file`, `exists`, `list_dir`,
/// `delete_file`, ...
#[derive(Debug, Clone)]
pub struct HarnessFs {
    inner: Arc<HarnessInner>,
}

/// env sub-handle: `get`, `set`, `vars`.
#[derive(Debug, Clone)]
pub struct HarnessEnv {
    inner: Arc<HarnessInner>,
}

/// random sub-handle: `gen_u64`, `gen_range`, `gen_f64`, ...
#[derive(Debug, Clone)]
pub struct HarnessRandom {
    inner: Arc<HarnessInner>,
}

/// net sub-handle: `http_get`, `http_post`, ...
#[derive(Debug, Clone)]
pub struct HarnessNet {
    inner: Arc<HarnessInner>,
}

macro_rules! sub_handle_inner {
    ($($ty:ty),* $(,)?) => {
        $(
            impl $ty {
                #[allow(dead_code)]
                pub(crate) fn inner(&self) -> &Arc<HarnessInner> {
                    &self.inner
                }
            }
        )*
    };
}
sub_handle_inner!(
    HarnessStdio,
    HarnessFs,
    HarnessEnv,
    HarnessRandom,
    HarnessNet,
);

impl HarnessClock {
    #[allow(dead_code)]
    pub(crate) fn inner(&self) -> &Arc<HarnessInner> {
        &self.inner
    }
}

/// Compact `VmValue` payload for a `Harness` or any of its sub-handles.
///
/// All seven variants share one `Arc<HarnessInner>`; `kind` discriminates the
/// surface the VM exposes for property access and method dispatch.
#[derive(Clone)]
pub struct VmHarness {
    inner: Arc<HarnessInner>,
    kind: HarnessKind,
}

impl VmHarness {
    pub fn kind(&self) -> HarnessKind {
        self.kind
    }

    pub fn type_name(&self) -> &'static str {
        self.kind.type_name()
    }

    pub fn inner(&self) -> &Arc<HarnessInner> {
        &self.inner
    }

    /// Get the sub-handle reached by a field name (`stdio`, `clock`, etc.).
    /// Returns `None` when the receiver is itself a sub-handle or the field
    /// is unknown.
    pub fn sub_handle(&self, field: &str) -> Option<VmHarness> {
        if self.kind != HarnessKind::Root {
            return None;
        }
        let kind = HarnessKind::from_field_name(field)?;
        Some(VmHarness {
            inner: Arc::clone(&self.inner),
            kind,
        })
    }
}

impl fmt::Debug for VmHarness {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("VmHarness")
            .field("kind", &self.kind)
            .finish_non_exhaustive()
    }
}

/// Clock wrapper that consults the crate-wide `clock_mock` thread-local
/// before delegating to an inner [`Clock`]. Used by [`Harness::real`] so
/// `harness.clock.*` reads honor `mock_time(...)` / `advance_time(...)`
/// during the E4.3-E4.6 migration. New tests should prefer
/// [`Harness::test`] / [`PausedClock`] directly.
#[derive(Debug)]
pub struct MockAwareClock<C: Clock + 'static> {
    inner: C,
}

impl<C: Clock + 'static> MockAwareClock<C> {
    pub fn new(inner: C) -> Self {
        Self { inner }
    }
}

#[async_trait]
impl<C: Clock + 'static> Clock for MockAwareClock<C> {
    fn now_utc(&self) -> OffsetDateTime {
        if let Some(mock) = crate::clock_mock::active_mock_clock() {
            return mock.now_utc();
        }
        self.inner.now_utc()
    }

    fn monotonic_ms(&self) -> i64 {
        if let Some(mock) = crate::clock_mock::active_mock_clock() {
            return mock.monotonic_ms();
        }
        self.inner.monotonic_ms()
    }

    async fn sleep(&self, duration: Duration) {
        if duration.is_zero() {
            return;
        }
        if let Some(mock) = crate::clock_mock::active_mock_clock() {
            // Single-script tests under `mock_time(...)` rely on `sleep(...)`
            // advancing the mock and returning immediately — the same
            // semantics as the legacy ambient `sleep_ms` builtin. Waiting
            // on `mock.sleep` would deadlock because nothing else is
            // driving `advance(...)` in the same task.
            mock.advance_std_sync(duration);
            return;
        }
        self.inner.sleep(duration).await;
    }

    async fn sleep_until_utc(&self, deadline: OffsetDateTime) {
        if let Some(mock) = crate::clock_mock::active_mock_clock() {
            let now = mock.now_utc();
            if deadline > now {
                if let Ok(delta) = Duration::try_from(deadline - now) {
                    mock.advance_std_sync(delta);
                }
            }
            return;
        }
        self.inner.sleep_until_utc(deadline).await;
    }
}

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

    #[test]
    fn real_constructs_without_panic() {
        let _harness = Harness::real();
    }

    #[test]
    fn sub_handles_share_inner_state() {
        let harness = Harness::real();
        let stdio_inner = Arc::as_ptr(harness.stdio().inner());
        let clock_inner = Arc::as_ptr(harness.clock().inner());
        assert_eq!(stdio_inner, clock_inner, "sub-handles share Arc<Inner>");
    }

    #[test]
    fn kinds_round_trip_through_field_names() {
        for kind in HarnessKind::SUB_HANDLES {
            let field = kind.field_name().unwrap();
            assert_eq!(HarnessKind::from_field_name(field), Some(*kind));
        }
        assert!(HarnessKind::from_field_name("nope").is_none());
        assert!(HarnessKind::Root.field_name().is_none());
    }

    #[test]
    fn vm_harness_property_access_returns_sub_handle() {
        let root = match Harness::real().into_vm_value() {
            crate::value::VmValue::Harness(h) => h,
            other => panic!("expected Harness variant, got {}", other.type_name()),
        };
        let stdio = root.sub_handle("stdio").expect("stdio sub-handle");
        assert_eq!(stdio.kind(), HarnessKind::Stdio);
        assert!(stdio.sub_handle("clock").is_none(), "nested access denied");
        assert!(root.sub_handle("not_a_field").is_none());
    }

    #[test]
    fn test_constructor_clock_advances_under_paused_clock_advance() {
        let (harness, paused) = Harness::test();
        let clock = harness.clock();
        let start_wall = clock.clock().now_utc();
        assert_eq!(start_wall, OffsetDateTime::UNIX_EPOCH);
        assert_eq!(clock.clock().monotonic_ms(), 0);

        paused.advance(Duration::from_millis(1_500));
        assert_eq!(clock.clock().monotonic_ms(), 1_500);
        let after_wall = clock.clock().now_utc();
        assert_eq!(after_wall - start_wall, time::Duration::milliseconds(1_500));
    }

    #[test]
    fn with_paused_clock_pins_origin() {
        let origin = OffsetDateTime::from_unix_timestamp(1_700_000_000).unwrap();
        let (harness, paused) = Harness::with_paused_clock(origin);
        assert_eq!(harness.clock().clock().now_utc(), origin);
        paused.advance(Duration::from_secs(60));
        assert_eq!(
            harness.clock().clock().now_utc() - origin,
            time::Duration::seconds(60)
        );
    }

    #[test]
    fn null_harness_records_deny_events_for_every_sub_handle() {
        let harness = Harness::null();
        for source in [
            r#"fn main(harness: Harness) { harness.stdio.println("blocked") }"#,
            r#"fn main(harness: Harness) { harness.clock.now_ms() }"#,
            r#"fn main(harness: Harness) { harness.fs.read_text("/x") }"#,
            r#"fn main(harness: Harness) { harness.env.get("KEY") }"#,
            r#"fn main(harness: Harness) { harness.random.gen_u64() }"#,
            r#"fn main(harness: Harness) { harness.net.get("https://example.test") }"#,
        ] {
            let error = run_harness_source(source, harness.clone()).expect_err("call denied");
            assert!(
                error.contains("NullHarness denied"),
                "unexpected deny error: {error}"
            );
        }

        let events = harness.deny_events();
        let observed: Vec<_> = events
            .iter()
            .map(|event| (event.sub_handle, event.method.as_str()))
            .collect();
        assert_eq!(
            observed,
            vec![
                (HarnessKind::Stdio, "println"),
                (HarnessKind::Clock, "now_ms"),
                (HarnessKind::Fs, "read_text"),
                (HarnessKind::Env, "get"),
                (HarnessKind::Random, "gen_u64"),
                (HarnessKind::Net, "get"),
            ]
        );
        assert_eq!(events[0].args, vec!["blocked"]);
        assert_eq!(events[2].args, vec!["/x"]);
    }

    #[test]
    fn mock_harness_replays_canned_responses_and_records_calls() {
        let harness = Harness::mock()
            .clock_at_unix_ms(1_700_000_000_000)
            .env("KEY", "value")
            .fs_read("/x", b"data".to_vec())
            .random_u64(42)
            .net_get("https://example.test", "body")
            .build();

        let output = run_harness_source(
            r#"
fn main(harness: Harness) {
  harness.stdio.print("partial ")
  harness.stdio.println("line")
  println(harness.clock.now_ms())
  harness.clock.sleep_ms(250)
  println(harness.clock.now_ms())
  println(harness.clock.monotonic_ms())
  println(harness.env.get("KEY"))
  println(harness.fs.read_text("/x"))
  println(harness.fs.exists("/missing"))
  println(harness.random.gen_u64())
  println(harness.net.get("https://example.test"))
}
"#,
            harness.clone(),
        )
        .expect("mock harness run succeeds");

        assert_eq!(harness.captured_stdio(), "partial line\n");
        assert_eq!(
            output,
            "1700000000000\n1700000000250\n250\nvalue\ndata\nfalse\n42\nbody\n"
        );
        let observed: Vec<_> = harness
            .calls()
            .into_iter()
            .map(|call| (call.sub_handle, call.method))
            .collect();
        assert_eq!(
            observed,
            vec![
                (HarnessKind::Stdio, "print".to_string()),
                (HarnessKind::Stdio, "println".to_string()),
                (HarnessKind::Clock, "now_ms".to_string()),
                (HarnessKind::Clock, "sleep_ms".to_string()),
                (HarnessKind::Clock, "now_ms".to_string()),
                (HarnessKind::Clock, "monotonic_ms".to_string()),
                (HarnessKind::Env, "get".to_string()),
                (HarnessKind::Fs, "read_text".to_string()),
                (HarnessKind::Fs, "exists".to_string()),
                (HarnessKind::Random, "gen_u64".to_string()),
                (HarnessKind::Net, "get".to_string()),
            ]
        );
    }

    #[test]
    fn mock_harness_replays_random_values_fifo() {
        let harness = Harness::mock()
            .random_u64(7)
            .random_u64(11)
            .random_u64(u64::MAX)
            .build();

        let output = run_harness_source(
            r#"
fn main(harness: Harness) {
  println(harness.random.gen_u64())
  println(harness.random.gen_u64())
  println(harness.random.gen_u64())
}
"#,
            harness,
        )
        .expect("mock random succeeds");

        assert_eq!(output, "7\n11\n9223372036854775807\n");
    }

    #[test]
    fn mock_harness_reports_missing_canned_responses() {
        let cases = [
            (
                r#"fn main(harness: Harness) { harness.fs.read_text("/missing") }"#,
                "MockHarness has no fs_read response for /missing",
            ),
            (
                r#"fn main(harness: Harness) { harness.random.gen_u64() }"#,
                "MockHarness has no random_u64 response",
            ),
            (
                r#"fn main(harness: Harness) { harness.net.get("https://missing.test") }"#,
                "MockHarness has no net_get response for https://missing.test",
            ),
        ];

        for (source, expected) in cases {
            let error = run_harness_source(source, Harness::mock().build())
                .expect_err("missing mock response fails");
            assert!(
                error.contains(expected),
                "expected `{expected}` in `{error}`"
            );
        }
    }

    #[test]
    fn mock_harness_records_failed_calls() {
        let harness = Harness::mock().build();
        let error = run_harness_source(
            r#"fn main(harness: Harness) { harness.net.get("https://missing.test") }"#,
            harness.clone(),
        )
        .expect_err("missing mock response fails");

        assert!(error.contains("MockHarness has no net_get response"));
        assert_eq!(
            harness.calls(),
            vec![HarnessCall {
                sub_handle: HarnessKind::Net,
                method: "get".to_string(),
                args: vec!["https://missing.test".to_string()],
            }]
        );
    }

    #[test]
    fn mock_harness_captures_stderr_separately_from_stdout() {
        let harness = Harness::mock().build();
        run_harness_source(
            r#"
fn main(harness: Harness) {
  harness.stdio.println("stdout line")
  harness.stdio.eprint("err ")
  harness.stdio.eprintln("trail")
}
"#,
            harness.clone(),
        )
        .expect("stderr capture run succeeds");
        assert_eq!(harness.captured_stdio(), "stdout line\n");
        assert_eq!(harness.captured_stderr(), "err trail\n");
    }

    #[test]
    fn mock_harness_replays_stdin_lines_for_read_and_prompt() {
        let harness = Harness::mock()
            .stdin_line("first")
            .stdin_line("second")
            .build();
        let output = run_harness_source(
            r#"
fn main(harness: Harness) {
  harness.stdio.println(harness.stdio.read_line())
  harness.stdio.println(harness.stdio.prompt("answer: "))
  let eof = harness.stdio.read_line({trim: false})
  harness.stdio.println(eof.status)
}
"#,
            harness.clone(),
        )
        .expect("stdin replay succeeds");
        // All stdio writes route to the mock capture buffer; vm.output stays empty.
        assert_eq!(output, "");
        assert_eq!(harness.captured_stdio(), "first\nanswer: second\neof\n");
    }

    #[test]
    fn mock_harness_rejects_wrong_argument_types() {
        let error = run_harness_source(
            r#"fn main(harness: Harness) { harness.fs.read_text(1) }"#,
            Harness::mock().build(),
        )
        .expect_err("wrong argument type fails");

        assert!(error.contains("HarnessFs.read_text expects string argument 1, got int"));
    }

    fn run_harness_source(source: &str, harness: Harness) -> Result<String, String> {
        let rt = tokio::runtime::Builder::new_current_thread()
            .enable_all()
            .build()
            .unwrap();
        rt.block_on(async move {
            let local = tokio::task::LocalSet::new();
            local
                .run_until(async move {
                    let chunk = crate::compile_source(source)?;
                    let mut vm = crate::Vm::new();
                    crate::stdlib::register_vm_stdlib(&mut vm);
                    vm.set_harness(harness);
                    vm.execute(&chunk)
                        .await
                        .map_err(|error| error.to_string())?;
                    Ok(vm.output().to_string())
                })
                .await
        })
    }
}