github/copilot-sdk · critical · InvalidOperationException

FFI runtime library not found at

Error message

FFI runtime library not found at '{fullLibraryPath}'.

What it means

FfiRuntimeHost.Create resolves the runtime cdylib path and verifies it exists before loading it. This InvalidOperationException reports the fully-resolved path when the native runtime library file is missing, failing fast instead of inside the native loader.

Solutions

1. Verify the resolved path in the message exists (ls / File.Exists) and fix libraryPath to point at the built cdylib (.so/.dylib/.dll)
2. Build/publish the native runtime for the target RID and include it in the output directory
3. Use an absolute path or resolve relative to AppContext.BaseDirectory instead of the current working directory

Example fix

// before
var host = FfiRuntimeHost.Create("libcopilot_runtime.so", ...);
// after
var libPath = Path.Combine(AppContext.BaseDirectory, "runtimes", "linux-x64", "native", "libcopilot_runtime.so");
var host = FfiRuntimeHost.Create(libPath, ...);

var full = Path.GetFullPath(libraryPath);
if (!File.Exists(full)) throw new FileNotFoundException($"FFI runtime library missing: {full}", full);

bool LibraryExists(string path) => File.Exists(Path.GetFullPath(path));

try { var host = FfiRuntimeHost.Create(libraryPath, ...); }
catch (InvalidOperationException ex) when (ex.Message.Contains("not found at")) { /* fix path / publish native lib */ throw new ApplicationException("Runtime library missing", ex); }

When it happens

Trigger: Calling Create with a libraryPath that does not exist on disk — wrong relative path, library not built/installed, wrong platform variant (linux-x64 vs osx), or insufficient resolve of a relative path from a different working directory.

Common situations: Deployment packages omit the native runtime binary; CI publishes for the wrong RID; app's working directory differs from dev so relative paths resolve differently; library deleted by cleanup or antivirus.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

• In-process FFI runtime library not found at
• FFI runtime library not found. Looked for
• An in-process FFI runtime library is already loaded from
• FFI runtime library not found at
• copilot_runtime_host_start failed

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/b1dfabb4c8c597c5. Report an issue: GitHub.

Appendix: source

Thrown at dotnet/src/FfiRuntimeHost.cs:78

        _logger = logger;
    }

    /// <summary>The stream JSON-RPC reads server→client frames from.</summary>
    public Stream ReceiveStream => _receiveStream;

    /// <summary>The stream JSON-RPC writes client→server frames to.</summary>
    public Stream SendStream => _sendStream
        ?? throw new InvalidOperationException("FfiRuntimeHost has not been started.");

    /// <summary>
    /// Loads the runtime cdylib and prepares the FFI host.
    /// </summary>
    public static FfiRuntimeHost Create(string libraryPath, string? cliEntrypoint, IReadOnlyDictionary<string, string>? environment, IReadOnlyList<string> args, ILogger logger)
    {
        var fullLibraryPath = Path.GetFullPath(libraryPath);
        if (!File.Exists(fullLibraryPath))
        {
            throw new InvalidOperationException($"FFI runtime library not found at '{fullLibraryPath}'.");
        }
        PrepareNativeLibrary(fullLibraryPath);
        return new FfiRuntimeHost(
            fullLibraryPath,
            cliEntrypoint is null ? null : Path.GetFullPath(cliEntrypoint),
            environment,
            args,
            logger);
    }

    /// <summary>
    /// The natural platform shared-library file name for the runtime cdylib, as
    /// emitted by the .NET build (the .node file renamed to what the Rust cdylib
    /// would be called on this OS).
    /// </summary>
    internal static string GetRuntimeLibraryFileName()
    {
        if (OperatingSystem.IsWindows()) return "copilot_runtime.dll";

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