ARCP — Agent Runtime Control Protocol (C# / .NET reference)

Reference C# / .NET 10 implementation of ARCP v1.1, the Agent Runtime Control Protocol — a transport-agnostic wire protocol for submitting, observing, and controlling long-running AI agent jobs.

Install

dotnet add package Arcp

Package	Purpose
Arcp	Umbrella meta-package; pulls Core + Client + Runtime.
Arcp.Core	Wire primitives — envelopes, messages, errors, IDs, transports, event log.
Arcp.Client	ArcpClient, JobHandle, JobEvent.
Arcp.Runtime	ArcpServer, JobManager, LeaseManager, SessionState.
Arcp.AspNetCore	IEndpointRouteBuilder.MapArcp("/arcp") over Kestrel.
Arcp.Otel	ITransport.WithTracing() — W3C trace propagation, ARCP span attributes.
Arcp.Hosting	IServiceCollection.AddArcpRuntime() for non-ASP.NET workers.
Arcp.Cli	arcp executable — serve, submit, version.

20-line quickstart

using Arcp.Client;
using Arcp.Core.Messages;
using Arcp.Core.Transport;
using Arcp.Runtime;

var server = new ArcpServer(new ArcpServerOptions
{
    Runtime = new RuntimeInfo { Name = "demo-runtime", Version = "1.0.0" },
});
server.RegisterAgent("echo", async (ctx, ct) =>
{
    await ctx.LogAsync("info", "received", ct);
    return ctx.Input;
});

var (clientTransport, serverTransport) = MemoryTransport.Pair();
_ = server.AcceptAsync(serverTransport);

await using var client = await ArcpClient.ConnectAsync(clientTransport, new ArcpClientOptions
{
    Client = new ClientInfo { Name = "demo-client", Version = "1.0.0" },
});
var handle = await client.SubmitAsync("echo", new { hi = 1 });
var result = await handle.Result;
// result.Success == true; result.Result.FinalStatus == "success"

v1.1 feature surface

Every feature ships behind a feature flag negotiated in session.hello / session.welcome (spec §6.2). The C# SDK advertises all of them by default:

Flag	Spec	Surface
heartbeat	§6.4	PeriodicTimer ping/pong; not counted in event_seq.
ack	§6.5	ArcpClient.AckAsync(long); runtime emits status{phase:"back_pressure"} when lag is high.
list_jobs	§6.6	ArcpClient.ListJobsAsync() returns paginated JobListEntrys.
subscribe	§7.6	ArcpClient.SubscribeAsync(jobId) returns a JobSubscription with IAsyncEnumerable<JobEvent>.
agent_versions	§7.5	AgentRef.Parse("name@version"); RegisterAgentVersion(); AGENT_VERSION_NOT_AVAILABLE.
progress	§8.2.1	JobContext.ProgressAsync(current, total?, units?, message?).
result_chunk	§8.4	JobContext.BeginResultStream() + WriteChunkAsync; JobHandle.Chunks().
lease_expires_at	§9.5	LeaseConstraints { ExpiresAt = DateTimeOffset }; watchdog emits LEASE_EXPIRED.
cost.budget	§9.6	BudgetAmount("USD:5.00") patterns; cost.* metrics decrement the ledger; BUDGET_EXHAUSTED.

Repository layout

src/
  Arcp.Core/           wire types, IDs, envelopes, transports, event log
  Arcp.Client/         ArcpClient + JobHandle
  Arcp.Runtime/        ArcpServer + JobManager + LeaseManager + SessionState
  Arcp/                umbrella package
  Arcp.AspNetCore/     IEndpointRouteBuilder.MapArcp("/arcp")
  Arcp.Otel/           ITransport.WithTracing()
  Arcp.Hosting/        IServiceCollection.AddArcpRuntime()
  Arcp.Cli/            arcp serve / submit
samples/               20 runnable demos covering v1.0 core + v1.1 features
tests/
  Arcp.UnitTests/        envelope, parsers, event log
  Arcp.IntegrationTests/ end-to-end flows over MemoryTransport
  Arcp.ConformanceTests/ one [Fact] per spec § requirement
  Arcp.AspNetCore.Tests/ loopback Kestrel + ClientWebSocket
docs/                  narrative documentation
docs/diagrams/         6 Graphviz pairs (light/dark)
planning/v1.1/         design plan

Run the samples

dotnet run --project samples/SubmitAndStream
dotnet run --project samples/Progress
dotnet run --project samples/ResultChunk
dotnet run --project samples/Heartbeat
dotnet run --project samples/CostBudget
dotnet run --project samples/AspNetCore   # listens on http://127.0.0.1:5519

Conformance

See CONFORMANCE.md — one row per spec § with a pointer to the test that demonstrates it.

Development

dotnet restore
dotnet build
dotnet test

Spec text lives in ../spec/docs/draft-arcp-02.1.md. The C#-specific plan that drove this implementation is at planning/v1.1/.