@@ -16,6 +16,7 @@ bytes = "1"
 cap-std = "4.0.3"
 http = "1"
 http-body-util = "0.1"
+hyperlight-host = { workspace = true, features = ["kvm", "mshv3", "hvf"] }
 hyper = { version = "1", features = ["server", "http1"] }
 hyper-util = { version = "0.1", features = ["tokio"] }
 log = "0.4"
 
@@ -17,6 +17,7 @@ pub use cap_fs::{
     CapFs, DescriptorFlags, DescriptorStat, DescriptorType, Dir, DirPerms, FilePerms,
     FilesystemLimits, FsError, OpenFlags,
 };
+pub use hyperlight_host::HyperlightError;
 pub use network::{HttpMethod, MethodFilter, NetworkPermission, NetworkPermissions};
 use serde::{Deserialize, Serialize};
 pub use tools::{ArgType, ToolRegistry, ToolSchema};
@@ -106,6 +107,30 @@ impl<T> Snapshot<T> {
 // Guest traits
 // ---------------------------------------------------------------------------
 
+/// An independently owned handle for interrupting guest execution.
+///
+/// Host callbacks are not interrupted. After an interruption, restore a
+/// snapshot before reusing the sandbox.
+#[derive(Clone)]
+pub struct InterruptHandle {
+    inner: std::sync::Arc<dyn hyperlight_host::hypervisor::InterruptHandle>,
+}
+
+impl InterruptHandle {
+    pub fn new(inner: std::sync::Arc<dyn hyperlight_host::hypervisor::InterruptHandle>) -> Self {
+        Self { inner }
+    }
+
+    /// Request interruption, returning whether the vCPU was running.
+    ///
+    /// This may block until the running vCPU stops. A false return during a
+    /// host callback can still leave cancellation pending until it returns.
+    /// A request just before guest entry can be missed; callers can retry.
+    pub fn kill(&self) -> bool {
+        self.inner.kill()
+    }
+}
+
 pub trait Guest: Sized {
     type Sandbox: GuestSandbox;
     fn build(
@@ -129,6 +154,10 @@ pub trait GuestSandbox: Send {
     fn snapshot(&mut self) -> Result<Snapshot<Self::SnapshotData>>;
     /// Restore a previously captured guest runtime state.
     fn restore(&mut self, snapshot: &Snapshot<Self::SnapshotData>) -> Result<()>;
+    /// Obtain an independently owned interruption handle.
+    fn interrupt_handle(&self) -> Result<InterruptHandle> {
+        anyhow::bail!("guest backend does not support interruption")
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -173,6 +202,10 @@ impl<G: Guest> Sandbox<G> {
         self.inner.run(code)
     }
 
+    pub fn interrupt_handle(&self) -> Result<InterruptHandle> {
+        self.inner.interrupt_handle()
+    }
+
     pub fn snapshot(&mut self) -> Result<Snapshot<<G::Sandbox as GuestSandbox>::SnapshotData>> {
         self.inner.snapshot()
     }
@@ -373,6 +406,12 @@ where
 mod tests {
     use super::*;
 
+    #[test]
+    fn interrupt_handle_is_send_and_sync() {
+        fn assert_send_sync<T: Send + Sync>() {}
+        assert_send_sync::<InterruptHandle>();
+    }
+
     struct TestGuest;
 
     struct TestGuestSandbox;
 
@@ -7,8 +7,8 @@ use hyperlight_js::{
 };
 use hyperlight_sandbox::runtime::BlockOn;
 use hyperlight_sandbox::{
-    CapFs, ExecutionResult, Guest, GuestSandbox, NetworkPermissions, SandboxConfig, Snapshot,
-    ToolRegistry, http as sandbox_http,
+    CapFs, ExecutionResult, Guest, GuestSandbox, InterruptHandle, NetworkPermissions,
+    SandboxConfig, Snapshot, ToolRegistry, http as sandbox_http,
 };
 use serde::Deserialize;
 
@@ -393,6 +393,15 @@ impl JsGuestSandbox {
                     exit_code: response.exit_code,
                 })
             }
+            Err(error)
+                if matches!(
+                    error,
+                    hyperlight_sandbox::HyperlightError::ExecutionCanceledByHost()
+                        | hyperlight_sandbox::HyperlightError::PoisonedSandbox
+                ) =>
+            {
+                Err(error.into())
+            }
             Err(error) => {
                 let mut stderr = error.to_string();
                 let stdout = match self.stdout.lock() {
@@ -415,6 +424,11 @@ impl JsGuestSandbox {
 impl GuestSandbox for JsGuestSandbox {
     type SnapshotData = JsSnapshot;
 
+    fn interrupt_handle(&self) -> Result<InterruptHandle> {
+        let handle = self.sandbox.interrupt_handle();
+        Ok(InterruptHandle::new(handle))
+    }
+
     fn run(&mut self, code: &str) -> Result<ExecutionResult> {
         self.run_impl(code)
     }
 
@@ -266,7 +266,8 @@ just dotnet copilot-sdk-example       # Run Copilot SDK example
 | Method | Description |
 |--------|-------------|
 | `Run(string code)` | Execute guest code, returns `ExecutionResult` |
-| `RunAsync(string, CancellationToken)` | Async version on thread pool |
+| `Run(string, CancellationToken)` | Execute guest code with interruption on cancellation |
+| `RunAsync(string, CancellationToken)` | Execute on the thread pool with interruption on cancellation |
 | `RegisterTool<TArgs,TResult>(name, handler)` | Register typed tool |
 | `RegisterTool(name, Func<string,string>)` | Register raw JSON tool |
 | `AllowDomain(target, methods?)` | Add domain to network allowlist |
@@ -275,6 +276,13 @@ just dotnet copilot-sdk-example       # Run Copilot SDK example
 | `Snapshot()` | Capture sandbox state |
 | `Restore(snapshot)` | Restore to captured state |
 
+Cancellation stops running guest execution on both backends and throws
+`OperationCanceledException` only after native execution and interruption callbacks
+have finished. Runtime initialization and host tool callbacks cannot be interrupted.
+Capture a snapshot before execution and restore it after cancellation before reusing
+the sandbox. Use a `CancellationTokenSource` with a finite timeout to bound guest
+execution; host tools must enforce their own cancellation policy.
+
 ### `ExecutionResult`
 
 | Property | Type | Description |
 
@@ -319,6 +319,21 @@ public void RegisterToolAsync(string name, Func<string, Task<string>> handler)
     /// permissions). Subsequent calls reuse the initialized runtime.
     /// </remarks>
     public ExecutionResult Run(string code)
+        => Run(code, CancellationToken.None);
+
+    /// <summary>Executes guest code with cancellation of running guest execution.</summary>
+    /// <param name="code">The code to execute.</param>
+    /// <param name="cancellationToken">Token used to interrupt guest execution.</param>
+    /// <returns>The execution result.</returns>
+    /// <remarks>
+    /// Runtime initialization and host callbacks cannot be interrupted.
+    /// Cancellation waits for native execution to stop before returning.
+    /// Completed results and unrelated failures are preserved if cancellation arrives late.
+    /// Restore a snapshot before reusing an interrupted sandbox.
+    /// </remarks>
+    /// <exception cref="OperationCanceledException">Thrown before execution if cancellation is
+    /// requested, or when native execution reports cancellation for this token.</exception>
+    public ExecutionResult Run(string code, CancellationToken cancellationToken)
     {
         lock (_gate)
         {
@@ -333,9 +348,43 @@ public ExecutionResult Run(string code)
                     nameof(code));
             }
 
-            var result = SafeNativeMethods.hyperlight_sandbox_run(_handle, code);
-            GC.KeepAlive(this);
-            result.ThrowIfError();
+            cancellationToken.ThrowIfCancellationRequested();
+            using var completed = new ManualResetEventSlim();
+            using var interruptHandle = cancellationToken.CanBeCanceled ? GetInterruptHandle() : null;
+            Task? interruption = null;
+            using var registration = cancellationToken.Register(() =>
+            {
+                // kill() can miss an idle guest just before native execution starts.
+                // Retry off the callback thread, which may itself be a host tool.
+                interruption = Task.Factory.StartNew(() =>
+                {
+                    while (!completed.IsSet)
+                    {
+                        if (SafeNativeMethods.hyperlight_sandbox_interrupt(interruptHandle!))
+                        {
+                            break;
+                        }
+
+                        completed.Wait(10);
+                    }
+                }, CancellationToken.None, TaskCreationOptions.LongRunning, TaskScheduler.Default);
+            });
+
+            FFIResult result;
+            try
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                result = SafeNativeMethods.hyperlight_sandbox_run(_handle, code);
+            }
+            finally
+            {
+                completed.Set();
+                registration.Dispose();
+                interruption?.GetAwaiter().GetResult();
+                GC.KeepAlive(this);
+            }
+
+            result.ThrowIfError(cancellationToken);
 
             var json = FFIResult.StringFromPtr(result.value);
             if (json == null)
@@ -359,14 +408,25 @@ public ExecutionResult Run(string code)
     /// For ASP.NET Core, prefer calling <see cref="Run"/> directly.
     /// </summary>
     /// <remarks>
-    /// The cancellation token prevents scheduling of the task but cannot
-    /// cancel an in-progress FFI call. Once <see cref="Run"/> starts
-    /// executing in the native layer, it will run to completion.
+    /// Cancellation interrupts running guest execution, but not runtime
+    /// initialization or host callbacks. Restore a snapshot after interruption.
     /// </remarks>
     /// <param name="code">The code to execute.</param>
-    /// <param name="cancellationToken">Token to prevent scheduling (does not cancel in-progress execution).</param>
+    /// <param name="cancellationToken">Token to prevent scheduling or interrupt running guest execution.</param>
     public Task<ExecutionResult> RunAsync(string code, CancellationToken cancellationToken = default)
-        => Task.Run(() => Run(code), cancellationToken);
+        => Task.Run(() => Run(code, cancellationToken), cancellationToken);
+
+    private InterruptSafeHandle GetInterruptHandle()
+    {
+        var result = SafeNativeMethods.hyperlight_sandbox_get_interrupt_handle(_handle);
+        result.ThrowIfError();
+        if (result.value == IntPtr.Zero)
+        {
+            throw new SandboxException("Native interruption handle was null.");
+        }
+
+        return new InterruptSafeHandle(result.value);
+    }
 
     // -----------------------------------------------------------------------
     // Network
 
@@ -33,4 +33,7 @@ internal enum FFIErrorCode : uint
 
     /// <summary>Filesystem I/O error.</summary>
     IoError = 7,
+
+    /// <summary>Guest execution was interrupted by the host.</summary>
+    Cancelled = 8,
 }
@@ -59,7 +59,7 @@ internal struct FFIResult
     /// Maps <see cref="FFIErrorCode"/> values to specific exception types
     /// for structured error handling in the API layer.
     /// </remarks>
-    public void ThrowIfError()
+    public void ThrowIfError(CancellationToken cancellationToken = default)
     {
         if (is_success)
         {
@@ -71,6 +71,8 @@ public void ThrowIfError()
 
         throw code switch
         {
+            FFIErrorCode.Cancelled when cancellationToken.IsCancellationRequested =>
+                new OperationCanceledException(errorMessage, cancellationToken),
             FFIErrorCode.Timeout =>
                 new SandboxTimeoutException(errorMessage),
             FFIErrorCode.Poisoned =>
 
@@ -103,3 +103,25 @@ protected override bool ReleaseHandle()
         return true;
     }
 }
+
+/// <summary>Owns a native interruption handle independently of sandbox state.</summary>
+internal sealed class InterruptSafeHandle : SafeHandle
+{
+    public InterruptSafeHandle(IntPtr handle) : base(IntPtr.Zero, ownsHandle: true)
+    {
+        SetHandle(handle);
+    }
+
+    public override bool IsInvalid => handle == IntPtr.Zero;
+
+    protected override bool ReleaseHandle()
+    {
+        IntPtr oldHandle = Interlocked.Exchange(ref handle, IntPtr.Zero);
+        if (oldHandle != IntPtr.Zero)
+        {
+            SafeNativeMethods.hyperlight_sandbox_free_interrupt_handle(oldHandle);
+        }
+
+        return true;
+    }
+}
@@ -214,6 +214,19 @@ internal static partial FFIResult hyperlight_sandbox_run(
         SandboxSafeHandle handle,
         [MarshalAs(UnmanagedType.LPUTF8Str)] string code);
 
+    [LibraryImport(LibName)]
+    [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+    internal static partial FFIResult hyperlight_sandbox_get_interrupt_handle(SandboxSafeHandle handle);
+
+    [LibraryImport(LibName)]
+    [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+    [return: MarshalAs(UnmanagedType.I1)]
+    internal static partial bool hyperlight_sandbox_interrupt(InterruptSafeHandle handle);
+
+    [LibraryImport(LibName)]
+    [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+    internal static partial void hyperlight_sandbox_free_interrupt_handle(IntPtr handle);
+
     // -----------------------------------------------------------------------
     // Filesystem
     // -----------------------------------------------------------------------
Original file line number	Diff line number	Diff line change
`@@ -33,4 +33,7 @@ internal enum FFIErrorCode : uint`
`33`	`33`
`34`	`34`	`/// <summary>Filesystem I/O error.</summary>`
`35`	`35`	`IoError = 7,`
	`36`	`+`
	`37`	`+ /// <summary>Guest execution was interrupted by the host.</summary>`
	`38`	`+ Cancelled = 8,`
`36`	`39`	`}`
Original file line number	Diff line number	Diff line change
`@@ -59,7 +59,7 @@ internal struct FFIResult`
`59`	`59`	`/// Maps <see cref="FFIErrorCode"/> values to specific exception types`
`60`	`60`	`/// for structured error handling in the API layer.`
`61`	`61`	`/// </remarks>`
`62`		`- public void ThrowIfError()`
	`62`	`+ public void ThrowIfError(CancellationToken cancellationToken = default)`
`63`	`63`	`{`
`64`	`64`	`if (is_success)`
`65`	`65`	`{`
`@@ -71,6 +71,8 @@ public void ThrowIfError()`
`71`	`71`
`72`	`72`	`throw code switch`
`73`	`73`	`{`
	`74`	`+ FFIErrorCode.Cancelled when cancellationToken.IsCancellationRequested =>`
	`75`	`+ new OperationCanceledException(errorMessage, cancellationToken),`
`74`	`76`	`FFIErrorCode.Timeout =>`
`75`	`77`	`new SandboxTimeoutException(errorMessage),`
`76`	`78`	`FFIErrorCode.Poisoned =>`