Voluta.OpenTelemetry 0.4.0

Stateful agent graphs for .NET — cycles, typed channels, checkpoints, streaming, and human-in-the-loop. You describe nodes and edges; Voluta runs them in Pregel-style supersteps and can pause a thread for days, then resume in another process.

→ cycles not DAGs
→ typed channels not dictionary soup
→ checkpoints not in-process memory
→ .NET-native not a Python port
→ AOT-ready core not a kitchen sink

v0.4.0 is on NuGet. Shipped surface is frozen (PublicAPI.Shipped.txt). Host time-travel (GetStateAsync / GetHistoryAsync / UpdateStateAsync / ForkAsync / Continue*) is available but still listed in PublicAPI.Unshipped.txt (can still move). dotnet add package Voluta --version 0.4.0 — see Quick Start.

See it in action

A ReAct-style loop (agent ⇄ tools) with no LLM — pure simulation so you can run it offline. Real output of dotnet run --project samples/HelloWorld:

  ◆  voluta · HelloWorld

  simulated ReAct · agent ⇄ tools · no LLM
  thread   react-sample-1
  stream   Updates
  ────────────────────────────────────────
  [agent] round 0 · requesting tools
  · step 1  Updates  [agent]
      status ← tools
      messages ← agent: call get_weather (round 1)
  [tools] executing simulated tool · round 1
  · step 2  Updates  [tools]
      tool_rounds ← 1
      messages ← tools: observation — temp=12C (round 1)
      status ← agent
  …
  [agent] enough tool data · finishing
  · step 5  Updates  [agent]
      status ← done
      messages ← agent: final answer — cloudy, 12°C in Oslo
  · step 5  End  [—]

  ▸ result
  status      Done
  ✓ done

The loop exists because one edge is conditional. messages accumulates (Append); status replaces (LastValue):

var graph = new StateGraph()
    .AddChannel("messages", ChannelKind.Append)
    .AddChannel("status", ChannelKind.LastValue)
    .AddChannel("tool_rounds", ChannelKind.LastValue)
    .AddNode("agent", AgentNodeAsync)
    .AddNode("tools", ToolsNodeAsync)
    .AddEdge(GraphConstants.Start, "agent")
    .AddConditionalEdges(
        "agent",
        static context => context.Read<string>("status") == "tools" ? "tools" : GraphConstants.End)
    .AddEdge("tools", "agent")
    .Compile(checkpointer, new CompileOptions { RecursionLimit = 32 });

await foreach (var item in graph.StreamAsync(
                   input,
                   new RunOptions { ThreadId = "react-1", StreamMode = StreamMode.Updates }))
{
    // item.Kind, item.NodeNames, item.Writes
}

<details> <summary><strong>Human-in-the-loop — interrupt, then resume (even later, another process)</strong></summary>

A node returns NodeResult.Interrupt instead of writes. The run stops, the checkpoint holds the payload, and ResumeInvokeAsync continues with a Command. Real output of samples/InterruptResume:

  ▸ invoke · expect interrupt

  · step 0  Start  [—]
  [gate] interrupting for human approval
  · step 1  Interrupt  [gate]
      payload ← { action = transfer, amount = 50, currency = USD }
  checkpoint  Interrupted

  ▸ resume · Command.Kind = approve

  [gate] resumed · payload=ok · approving
  · step 2  End  [—]
  status      Done
  ✓ done

static Task<NodeResult> GateNodeAsync(GraphContext context, CancellationToken cancellationToken)
{
    if (!context.IsResume)
    {
        return Task.FromResult<NodeResult>(
            NodeResult.Interrupt(new { action = "transfer", amount = 50, currency = "USD" }));
    }

    return Task.FromResult<NodeResult>(
        NodeResult.Continue(new ChannelWrite("messages", "gate: transfer approved")));
}

// first process
var terminal = await graph.InvokeAsync(input, new RunOptions { ThreadId = "hitl-1" });
// terminal.Kind == StreamEventKind.Interrupt

// later — same or new process, same checkpointer root / store
// closed kinds: Command.Approve / Reject / Update (Command.Kinds.*)
var done = await graph.ResumeInvokeAsync(
    "hitl-1",
    Command.Approve(
        "ok",
        // optional: patch channels before the node re-runs
        new Dictionary<string, object?> { ["decision"] = "go" }));

</details>

<details> <summary><strong>Time-travel read (GetState / GetHistory)</strong></summary>

ICheckpointer is the storage seam (shipped). There is no putWrites — a put is always a full C-shape snapshot:

Method	Contract
PutAsync(CheckpointSnapshot)	Persist this snapshot (and its step in history when the provider supports it)
GetAsync(threadId)	Latest snapshot only. Miss returns null (does not throw)
ListAsync(threadId)	Full step history, oldest first. Providers that cannot list must throw NotSupportedException rather than return a silent partial

InMemory, File, EF, S3, and Redis all implement history. IVolutaStore is a separate cross-thread KV (Put/Get/List/Delete by namespace) — ListAsync(namespace) lists all keys in that namespace, not checkpoints.

Host-facing projection — no need to spelunk C-shape fields. These methods are available (PublicAPI.Unshipped.txt, not frozen):

// latest snapshot for ops / HTTP / UI  (wraps ICheckpointer.GetAsync)
var state = await graph.GetStateAsync("order-9");
// state?.Status, state?.Step, state?.Values, state?.InterruptPayload

// full step history, oldest first  (wraps ICheckpointer.ListAsync)
var history = await graph.GetHistoryAsync("order-9");
// ordered by Step ascending; history[^1] matches GetState when present

Ops UI: GET /voluta/api/threads/{id}/history lists steps; inspector shows them after Load.

</details>

<details> <summary><strong>Update state / fork / continue</strong></summary>

Ops and support workflows can edit channel values and branch threads without re-invoking from scratch. There is no putWrites. Channel edits go through UpdateStateAsync(threadId, IEnumerable<ChannelWrite>) (Unshipped): it loads the latest checkpoint, applies the same LastValue / Append reducers as runtime input seeding, and Puts a new history step.

// patch latest checkpoint (Append / LastValue reducers apply)
var patched = await graph.UpdateStateAsync(
    "order-9",
    [new ChannelWrite("messages", "ops-note")]);

// branch a new thread from history step N (same step index on the new thread)
var fork = await graph.ForkAsync(sourceThreadId: "order-9", step: 2, newThreadId: "order-9-retry");

// re-drive a Running thread after update/fork (not for Interrupted — use Resume*)
// WARNING: nodes in NextNodes re-execute; make side effects idempotent
var terminal = await graph.ContinueInvokeAsync("order-9-retry");

• Interrupted → still use ResumeAsync / ResumeInvokeAsync (optionally after UpdateStateAsync).
• Done → UpdateStateAsync may still patch values; Continue* throws graph.invalid_continue.
• Failed/Cancelled → update promotes status to Running so continue can re-drive last NextNodes.

</details>

<details> <summary><strong>Typed state with <code>[GraphState]</code> (source generator)</strong></summary>

String channel names work. When you want compile-time names and updates that only write what you set:

[GraphState]
public partial class ReviewState
{
    [Channel(ChannelKind.Append)]
    public IList<object?> Notes { get; set; } = new List<object?>();

    [Channel(ChannelKind.LastValue)]
    public string? Verdict { get; set; }
}

var graph = new StateGraph()
    .AddChannels(ReviewState.CreateSchema())
    .AddNode(
        "review",
        static (context, cancellationToken) => Task.FromResult<NodeResult>(
            NodeResult.Continue(
                new ReviewState.ReviewStateUpdate { Verdict = "approved" }.ToWrites())))
    .AddEdge(GraphConstants.Start, "review")
    .AddEdge("review", GraphConstants.End)
    .Compile(new InMemoryCheckpointer());

Unset properties emit no write. An explicit null is a clear. Interface-typed properties use OptionalValue<T>.Of(value).

</details>

<details> <summary><strong>Typed channels and custom reducers</strong></summary>

Checkpoints stay dumb JSON (allow-listed primitives / lists / string-key dicts). Types live on the compiled graph. AddChannel<T> records T so restore coerces wire values (long → int, JSON object text → Dictionary<string, string>, append list elements to string). Untyped AddChannel(name, kind) still works and coexists on the same graph.

var graph = new StateGraph()
    .AddChannel<int>("score", ChannelKind.LastValue)
    .AddChannel<string>("messages", ChannelKind.Append)
    .AddChannel("notes", ChannelKind.Append) // untyped
    .AddChannel<Dictionary<string, object?>>("artifacts", new DictMergeReducer())
    .AddNode("left", LeftAsync)
    .AddNode("right", RightAsync)
    .AddEdge(GraphConstants.Start, "left")
    .AddEdge(GraphConstants.Start, "right")
    .AddEdge("left", GraphConstants.End)
    .AddEdge("right", GraphConstants.End)
    .Compile(checkpointer);

IChannelReducer is public; IChannel stays internal. Built-ins: LastValueReducer, AppendReducer, DictMergeReducer. Custom reducers use a separate AddChannel(name, reducer) overload — ChannelKind stays LastValue | Append. Durable restore contract: FileCheckpointerRuntimeShould.RehydrateTypedChannelsViaDeclaredValueType.

</details>

<details> <summary><strong>Durable file checkpoint (survive process restart)</strong></summary>

// Host DI (recommended) — same root on every process
services.AddVoluta(v =>
{
    v.Checkpoints.UseFile("/var/lib/voluta/threads");
    v.Graph((sp, checkpointer) => new StateGraph()
        // … nodes …
        .Compile(checkpointer, new CompileOptions { Services = sp }));
});

// process A
var graph = sp.GetRequiredService<CompiledGraph>();
await graph.InvokeAsync(input, new RunOptions { ThreadId = "order-9" });
// → Interrupted

// process B (new host, same UseFile root) — resume
await graph.ResumeInvokeAsync("order-9", Command.Approve("ok"));

Values serialize with System.Text.Json — prefer JSON-friendly types (strings, numbers, lists of primitives). Durable rehydrate is lossy: File / EF / S3 / Redis FromElement restores string / bool / long / double and arrays as List<object?>. JSON objects ({}) become GetRawText() — a JSON string, not the original CLR type and usually not JsonElement. InMemoryCheckpointer keeps CLR references (no JSON). Declare AddChannel<T> so the compiled graph coerces those wire values on restore. Custom POCOs still fail Put unless they are allow-listed shapes.

For tests, InMemoryCheckpointer is enough; every storage implements ICheckpointer and can run CheckpointerConformance.RunAllAsync. Provider types (FileCheckpointer, EF, S3, Redis) are constructed via Use* only — not new.

</details>

<details> <summary><strong>Fan-out with <code>Send</code> / subgraphs</strong></summary>

// Map one item to many dynamic tasks (runtime-scheduled nodes)
return NodeResult.ContinueWithSends(
    new Send("worker", payload: orderLine1),
    new Send("worker", payload: orderLine2));

// Nest a compiled graph as a single node (stable child thread: parentId/child)
.AddNode("child", Subgraph.AsNode(
    childCompiledGraph,
    inputChannels: ["messages"],
    outputChannels: ["result"]));
// Custom multi-agent nest namespace:
// threadIdFactory: ctx => $"{ctx.ThreadId}/agent/{ctx.NodeName}"

Child interrupt → parent interrupt (same HITL Command resume on the parent thread resumes the nested child). Default nested checkpoint key: {parentThreadId}/{nodeName}.

CompiledGraph.Describe() returns topology (nodes, edges, channels) for the ops UI or docs.

</details>

<details> <summary><strong>Host with DI + ops console</strong></summary>

// Program.cs
builder.Services.AddVoluta(sp =>
{
    var checkpointer = sp.GetRequiredService<ICheckpointer>();
    return new StateGraph()
        // …
        .Compile(checkpointer);
});

// Optional ops UI (ASP.NET)
var session = new VolutaUiSession(graph, checkpointer);
builder.Services.AddVolutaUI(session);
app.MapVolutaUI(options => options.PathPrefix = "/voluta");
app.MapStudioApi(); // versioned /api/v1 for the SPA and any FE client
// → Studio SPA:  http://localhost:5188/voluta/studio
// → Legacy shell: http://localhost:5188/voluta  (see samples/UiHost)

</details>

<details> <summary><strong>Testing without fighting the runtime</strong></summary>

Voluta.Testing ships doubles you’d otherwise write by hand:

Helper	Role
RecordingCheckpointer	Records every Put/Get/List
FaultInjectingCheckpointer	Fails the n-th write
CheckpointerConformance.RunAllAsync	Suite every ICheckpointer must pass
GraphFixtures.Linear() / .Cycle() / .Interrupt()	Ready graphs
StreamCapture	Drain a stream in tests

Unit tests cover linear/conditional/cycle, fan-out, Send, HITL (Command.Values, resume payload), stream modes (Updates / Events), Append flatten vs string, LastValue sequential overwrite, and File rehydrate + resume.

dotnet test voluta.slnx

</details>

<details> <summary><strong>Sample: Hybrid-style marketing desk (mock tools)</strong></summary>

Not a product agent — a demo that exercises the graph against Hybrid console.platform nouns (Campaign, SSP, DirectDeal, AdLibrary):

# terminal 1
dotnet run --project samples/MockAdMcp          # http://localhost:5190

# terminal 2
dotnet run --project samples/MarketingAgent -- --offline

Flow: brief → creative → setup (create RK → SSP → banner → Active) → review. Tools are a simplified HTTP tools surface for demos — not the official MCP SDK and not live Hybrid API.

</details>

Why Voluta

• Cycles are the point — think → act → observe is a loop. Conditional edges + RecursionLimit make loops terminate on purpose.
• The run outlives the process — every superstep can checkpoint. Interrupt, inspect, resume, or replay from storage; ICheckpointer is the only seam.
• Multi-writer state is defined — same-superstep writes go through reducers (Append / LastValue). Concurrent LastValue writers fail fast instead of last-write-wins races.
• Core stays small — Voluta + Abstractions + DI are IsAotCompatible, zero third-party deps on the hot path. No LLM SDK, no logging framework required to run a graph.

Voluta is orchestration, not a Claude Code / OpenCode clone. You bring tools, MCP, prompts, and policy; Voluta runs the stateful graph.

Quick Start

Requires .NET 10 SDK (dotnet --version ≥ 10.0.100).

Scaffold a HITL agent (no clone required once the template pack is installed):

dotnet new install Voluta.Templates
dotnet new voluta-agent -n MyAgent
cd MyAgent && dotnet run

Or clone and run in-repo samples:

git clone https://github.com/dot-stbl/voluta.git
cd voluta
dotnet build voluta.slnx
dotnet run --project samples/HelloWorld
dotnet run --project samples/InterruptResume

Reference from your app:

dotnet add package Voluta --version 0.4.0
# or, from a clone:
dotnet add reference path/to/voluta/src/Voluta/Voluta.csproj

Minimal complete program

Writer + critic loop until score ≥ 8 — prints End after N supersteps:

using Voluta;
using Voluta.Abstractions.Channels;
using Voluta.Abstractions.Results;
using Voluta.Abstractions.Runtime;
using Voluta.Checkpoint;
using Voluta.Graph;
using Voluta.Graph.Builder;
using Voluta.Graph.Options;

var graph = new StateGraph()
    .AddChannel("draft", ChannelKind.LastValue)
    .AddChannel("notes", ChannelKind.Append)
    .AddChannel("score", ChannelKind.LastValue)
    .AddNode("write", WriteAsync)
    .AddNode("critique", CritiqueAsync)
    .AddEdge(GraphConstants.Start, "write")
    .AddEdge("write", "critique")
    .AddConditionalEdges(
        "critique",
        static context => (context.Read<int?>("score") ?? 0) < 8 ? "write" : GraphConstants.End)
    .Compile(new InMemoryCheckpointer(), new CompileOptions { RecursionLimit = 16 });

var final = await graph.InvokeAsync(
    [new ChannelWrite("draft", "checkpoints are nice")],
    new RunOptions { ThreadId = "post-42" });

Console.WriteLine($"{final.Kind} after {final.Step} supersteps");

static Task<NodeResult> WriteAsync(GraphContext context, CancellationToken cancellationToken)
{
    var round = (context.Read<int?>("score") ?? 0) / 4;
    return Task.FromResult<NodeResult>(
        NodeResult.Continue(
            new ChannelWrite("draft", $"revision {round + 1}"),
            new ChannelWrite("notes", $"writer: produced revision {round + 1}")));
}

static Task<NodeResult> CritiqueAsync(GraphContext context, CancellationToken cancellationToken)
{
    var score = (context.Read<int?>("score") ?? 0) + 4;
    return Task.FromResult<NodeResult>(
        NodeResult.Continue(
            new ChannelWrite("score", score),
            new ChannelWrite("notes", $"critic: scored {score}/10")));
}

Swap InvokeAsync for StreamAsync (StreamMode.Values / Updates / Events). Under a host: services.AddVoluta(provider => …).

DI nodes + Microsoft AI (optional)

Native path — no extension-method glue:

// 1) IGraphNode + DI (core)
services.AddSingleton<PlanNode>();
services.AddVoluta(v =>
{
    v.Checkpoints.UseInMemory();
    v.Graph((sp, checkpointer) => new StateGraph()
        .AddNode<PlanNode>("plan")
        .AddEdge(GraphConstants.Start, "plan")
        .AddEdge("plan", GraphConstants.End)
        .Compile(checkpointer, new CompileOptions { Services = sp }));
});

// 2) MEAI IChatClient as a node (Voluta.Agents.AI)
ChatClientNodes.Add(
    graph, "answer", "answer",
    context => [new ChatMessage(ChatRole.User, context.Read<string>("question") ?? "")],
    stream: true,
    usageChannel: "usage",
    toolCallsChannel: "tool_calls");

// 3) Microsoft Agent Framework AIAgent as a node
AgentNodes.Add(graph, "research", agent, outputChannel: "draft", inputChannel: "question");

ChatClientNodes covers: assistant text → OutputChannel; optional Stream token deltas via GraphContext.Stream (StreamEventKind.Messages); optional UsageChannel (ChatClientUsage from ChatResponse.Usage, best-effort on stream from UsageContent); optional ToolCallsChannel (Append-friendly List<object?> of ChatClientToolCall, empty when the model made no calls). Windowing and ReAct routing stay in the host graph.

Long-running / workers

HITL and multi-minute agent turns must not pin to an HTTP request. Pattern:

1. Wake a threadId (queue, bus, or in-process channel).
2. Invoke or ResumeInvoke until the stream hits interrupt / end / fail.
3. Park on interrupt (checkpoint is source of truth — process may exit).
4. Complete on done; dead-letter / alert on fail (last-good checkpoint remains; do not ResumeInvoke a Failed thread).

Package: Voluta.Hosting — IThreadWakeBus, InMemoryThreadWakeBus, GraphThreadRunner, GraphWorkerService, AddVolutaWorkerHosting(). Sample: samples/WorkerHost. No Hangfire/Quartz; NATS/SQS are host-owned implementations of the interface.

services.AddVoluta(v => { /* checkpoints + graph */ });
services.AddVolutaWorkerHosting(); // IThreadWakeBus + BackgroundService worker

// producer (HTTP approve, bus consumer, …)
await wakes.EnqueueAsync(ThreadWake.Start(threadId, inputWrites));
// later, after human approval:
await wakes.EnqueueAsync(ThreadWake.Resume(threadId, Command.Approve("ok")));

Multi-instance (k8s scale-out)

• Use a shared durable checkpointer (File / EF / S3 / Redis), not in-memory, across replicas.
• Wakes are hints; the checkpoint decides invoke vs resume vs already-terminal.
• Partition or lease by threadId so two pods do not run the same thread at once.
• Use a shared durable checkpointer (File / EF / S3 / Redis), not in-memory, across replicas. Checkpointer is the source of truth; wakes are only hints.
• Replace InMemoryThreadWakeBus with a durable queue implementing IThreadWakeBus.
• Partition or lease by threadId so two pods do not run the same thread at once (GraphWorkerService only dedupes in-flight wakes within one process).
• Interrupt park is multi-process safe: pod A parks, pod B resumes hours later against the same store.

Host DI — AddVoluta

One composition root: checkpoints + graph (and later UI hooks). Prefer this over raw AddSingleton<ICheckpointer>(…) / ad-hoc factories.

// Recommended: checkpoints + graph in one call
services.AddVoluta(v =>
{
    v.Checkpoints.UseInMemory(); // or UseFile / UseEntityFrameworkCore / UseS3 / UseRedis
    v.Graph((sp, checkpointer) => new StateGraph()
        // …nodes, edges, channels…
        .Compile(checkpointer, new CompileOptions { Services = sp }));
});

// Graph only (already compiled, or factory that owns its own checkpointer)
services.AddVoluta(prebuiltGraph);
services.AddVoluta(sp => BuildGraph(sp));

// Checkpoints only (resolve ICheckpointer yourself)
services.AddVolutaCheckpoints(c => c.UseFile("./.voluta/checkpoints"));

Checkpoint providers (v.Checkpoints.Use*)

Exactly one Use* per host:

v.Checkpoints.UseInMemory();
v.Checkpoints.UseFile("./.voluta/checkpoints");

// EF — register IDbContextFactory first (any provider: Npgsql, SqlServer, SQLite, …)
services.AddDbContextFactory<AppDbContext>(o => o.UseNpgsql(connectionString));
v.Checkpoints.UseEntityFrameworkCore<AppDbContext>();

// S3 — register IAmazonS3 first
services.AddSingleton<IAmazonS3>(_ => new AmazonS3Client(RegionEndpoint.EUCentral1));
v.Checkpoints.UseS3(o =>
{
    o.BucketName = "voluta";
    o.KeyPrefix = "runs";
});

// Redis — register IConnectionMultiplexer first
services.AddSingleton<IConnectionMultiplexer>(_ => ConnectionMultiplexer.Connect("localhost:6379"));
v.Checkpoints.UseRedis(o =>
{
    o.KeyPrefix = "voluta:";
    // o.Database = 0;
});

<details> <summary><strong>Host DbContext shape (EF)</strong></summary>

public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
    : DbContext(options), IVolutaCheckpointDbContext
{
    public DbSet<CheckpointRecord> Checkpoints => Set<CheckpointRecord>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyVolutaCheckpointModel(); // table voluta_checkpoints
        // …your entities…
    }
}

Schema ownership is yours: migrations or EnsureCreated() in tests. Column names follow your EF naming convention (no forced snake_case). Snapshot payload is a JSON column via EF value conversion — the checkpointer itself does not call JsonSerializer.

</details>

<details> <summary><strong>Errors and limits</strong></summary>

• Miss on Get → null (not an exception).
• Storage failures → CheckpointStoreException with stable Code (checkpoint.put_failed / get_failed / list_failed). Graph logic still uses GraphException and friends.
• Channel values (wire format v1) on File / EF / S3 / Redis: allow-list only — null, primitives, string, Guid, date/time, JsonElement, byte[], lists and string-key dictionaries of those (depth ≤ 8). Unsupported types fail Put with checkpoint.unsupported_value_type (no silent loss). InMemory is process-local and does not enforce the allow-list.
• S3 keys: {prefix}/{safeThreadId}/{step:D12}.json.

Every provider is exercised by CheckpointerConformance.RunAllAsync in Voluta.Testing (InMemory, File, EF SQLite + EF InMemory, S3 with a fake client).

Full code + EventId catalog and host HTTP mapping sample: Error codes & EventIds.

</details>

Error codes & EventIds

Voluta does not ship an ASP.NET package. Exceptions carry a stable Code (dot.case); hosts map codes to HTTP/gRPC/worker outcomes themselves. Catalog types:

Type	Package	Role
VolutaErrorCodes	Voluta.Abstractions	Stable code strings
VolutaEventIds	Voluta	MEL EventId (id + name = code)
VolutaExceptionLogging.GetEventId(...)	Voluta	Code / exception → EventId

Log full exception + Code + EventId; never put secrets or PII in Message.

catch (GraphException exception)
{
    logger.LogError(
        VolutaExceptionLogging.GetEventId(exception),
        exception,
        "Graph failed with {ErrorCode}",
        exception.Code);
    // host maps exception.Code → ProblemDetails / status
}

Code → suggested HTTP status (host sample)

Code	Typical status	Notes
graph.invalid_* / graph.duplicate_* / graph.no_nodes / graph.missing_start / graph.unknown_endpoint	400	Compile-time topology errors
graph.invalid_resume	409	Resume when thread is not interrupted
graph.out_of_steps	422 or 400	Recursion limit; product choice
graph.run_failed	500	Uncaught node/superstep fault
channel.concurrent_update	409	LastValue multi-writer in one superstep
checkpoint.put_failed / get_failed / list_failed / corrupt_payload	502 / 500	Store / IO / corrupt payload
checkpoint.unsupported_format_version	409 or 500	Wire newer than this package
checkpoint.unsupported_value_type	400	Reserved (serde #31)
command.invalid_kind / command.invalid_payload	400	Reserved (command taxonomy #32)

Get miss stays null — not an exception. Interrupt control flow stays NodeResult.Interrupt (not exceptions).

<details> <summary><strong>Failure & recovery (checkpoint policy)</strong></summary>

When a node throws, a superstep merge fails, or the recursion limit is hit:

1. Stream surfaces a Failed event (and the invoke/stream API rethrows the graph fault).
2. Checkpoint Put writes a terminal snapshot at the failing superstep with GraphRunStatus.Failed (or Cancelled on cooperative cancel). Incomplete writes from the failed superstep are not applied.
3. Channel values on that terminal snapshot are the last successful apply — last-good payload, not a wipe and not a half-merge.
4. Get returns that latest terminal document (Status = Failed, last-good channels).
5. List (when supported) still enumerates earlier Running / Interrupted / Done steps for tooling; prior step keys are never overwritten by the failure put.
6. Resume (ResumeInvokeAsync) still requires Interrupted — Failed/Cancelled are terminal for HITL resume. Hosts re-invoke with a new thread, or rebuild input from last-good channels / list history.

Contracts: openspec/specs/error-cancellation/.

</details>

How a superstep works

One tick, in order: collect ready nodes → run them concurrently → barrier → merge writes through channel reducers → checkpoint → evaluate edges.

• Nodes in the same superstep never see each other’s writes (barrier isolation).
• Conditional edges run after the merge, on committed state.

Contracts: openspec/specs/ (12 capabilities).

How it compares

vs. LangGraph (Python) — Origin of the execution model (supersteps, channels, checkpoint-first). Voluta rebuilds the surface on .NET generics, typed reducers, and IAsyncEnumerable. Not a port; a peer.

vs. Microsoft Agent Framework — Better for multi-agent chat and function calling. It does not give cyclic graphs with durable per-thread state. Compose: run MAF agents inside Voluta nodes.

vs. Durable Functions / Durable Task — Stronger storage ecosystem for business workflows. Orchestrator + replay vs graph + explicit channels — Voluta fits think-act-observe loops more directly.

vs. a hand-rolled while — Works until “state at step 7?”, “resume after restart?”, or “two nodes wrote the same field”. Those three questions are the library.

Packages

How-to for checkpoints (DI Use* + host DbContext) is under Durable checkpoints. Behavior contracts: openspec/specs/checkpoint/. Until NuGet publishes, browse source under src/ (each package is one folder; no per-package README yet).

Package	Role	Source
Voluta.Abstractions	Contracts: channels, checkpoints, NodeResult, Send, streaming	src/core/Voluta.Abstractions
Voluta	Pregel runtime + InMemory + Subgraph.AsNode + Describe()	src/core/Voluta
Voluta.DependencyInjection	AddVoluta(v => { v.Checkpoints…; v.Graph… })	src/core/Voluta.DependencyInjection
Voluta.OpenTelemetry	AddVolutaInstrumentation() for OTel Tracer/Meter providers	src/hosting/Voluta.OpenTelemetry
Voluta.Generators	[GraphState] source generator	src/devtools/Voluta.Generators
Voluta.Testing	Test doubles + checkpointer conformance suite	src/devtools/Voluta.Testing
Voluta.Checkpoints.File	JSON file-system checkpointer (UseFile)	src/checkpoints/Voluta.Checkpoints.File
Voluta.Checkpoints.EntityFrameworkCore	Provider-agnostic EF Core (UseEntityFrameworkCore<T>)	src/checkpoints/Voluta.Checkpoints.EntityFrameworkCore
Voluta.Checkpoints.S3	AWS S3 / S3-compatible (UseS3)	src/checkpoints/Voluta.Checkpoints.S3
Voluta.Checkpoints.Redis	Redis sorted-set checkpointer (UseRedis)	src/checkpoints/Voluta.Checkpoints.Redis
Voluta.Agents.AI	MAF AIAgent + MEAI as IGraphNode	src/agents/Voluta.Agents.AI
Voluta.Hosting	Wake bus + GraphWorkerService presets	src/hosting/Voluta.Hosting
Voluta.UI	Studio SPA (React + Fluent) + legacy shell + /api/v1 via MapStudioApi	src/ops/Voluta.UI

Native AOT applies to the core tier only — Voluta, Abstractions, and DependencyInjection are IsAotCompatible, with a publish smoke test in samples/AotSmoke. Checkpoint providers (File / EF / S3 / Redis), UI, Agents.AI, Hosting, and OpenTelemetry are regular-CLR packages and do not claim AOT.

OpenTelemetry

Core Voluta always emits BCL ActivitySource / Meter named "Voluta" (no OTel SDK dependency). Wire the SDK with Voluta.OpenTelemetry:

using OpenTelemetry.Metrics;
using OpenTelemetry.Trace;
using Voluta.OpenTelemetry;

builder.Services.AddOpenTelemetry()
    .WithTracing(tracing => tracing
        .AddVolutaInstrumentation()
        .AddOtlpExporter())
    .WithMetrics(metrics => metrics
        .AddVolutaInstrumentation()
        .AddOtlpExporter());

Spans: voluta.superstep, voluta.node.execute, voluta.checkpoint.put|get|list.
Metrics: voluta.superstep.duration, voluta.node.duration (ms), voluta.interrupt.count, voluta.checkpoint.*.count, voluta.stream.dropped. Tags: node.name, run.status, error.type, provider.name, stream.kind (no raw thread ids).

No library ILogger output — hosts log exceptions via VolutaExceptionLogging.GetEventId

• VolutaErrorCodes. Full catalog: docs/0.x/concepts/observability.mdx.

<details> <summary><strong>Production hardening (Continue / multi-HITL / stream)</strong></summary>

• Continue with PendingSends: schedules incomplete push tasks only — does not re-pull NextNodes (avoids double side effects after a completed map+Send).
• Multi-interrupt: Command.Resumes may be a partial map; remaining PendingInterrupts stay Interrupted until covered. Unknown task ids fail command.invalid_payload.
• Live Custom/Messages: bounded buffer (capacity 256); overflow drops and increments voluta.stream.dropped (stream.kind tag). Order is best-effort per node.

See OpenSpec checkpoint / hitl-interrupt / streaming and issue #63.

</details>

Samples

Sample	What it shows
HelloWorld	Cyclic agent ⇄ tools, StreamMode.Updates
InterruptResume	HITL interrupt + Command resume
AotSmoke	Native AOT publish smoke
ReviewBot	CLI: plan → sandbox tools → review (+ optional HITL)
DocQ	Docs Q&A over a sandboxed folder
MarketingAgent	Hybrid desk setup over mock tools
MockAdMcp	Hybrid-shaped tool server (Campaign / SSP / deal / AdLibrary)
UiHost	ASP.NET host: MapVolutaUI + MapStudioApi + Studio SPA
StudioHost	Studio /api/v1 contract host with seeded demo threads
WorkerHost	Durable BackgroundService runner (wake / park / resume)

Index: samples/README.md.

dotnet run --project samples/HelloWorld
dotnet run --project samples/InterruptResume
dotnet run --project samples/WorkerHost
dotnet run --project samples/ReviewBot -- --offline --root .
dotnet run --project samples/DocQ -- --offline --root . --question "What is Voluta?"
dotnet run --project samples/MockAdMcp          # :5190
dotnet run --project samples/MarketingAgent -- --offline
dotnet run --project samples/UiHost             # Studio: http://localhost:5188/voluta/studio

What isn't here yet

Stated plainly so you can judge the fit:

• PublicAPI surface can still move before a major bump (tracked with PublicApiAnalyzers). Shipped surface up to v0.4.0 is frozen in PublicAPI.Shipped.txt. Host time-travel (GetStateAsync / GetHistoryAsync / UpdateStateAsync / ForkAsync / Continue*) is available but still Unshipped.
• Studio SPA auth is not built in; /api/v1 supports an optional single API key (StudioApiOptions.ApiKey). Multi-tenant auth is out of scope for now.
• Checkpoint serde is JSON at the store; AddChannel<T> coerces declared types on restore (see Typed channels and Durable file checkpoint). Versioning/evolution is still open.
• MCP in samples is a light HTTP bridge (inlined in MarketingAgent), not a product package; real MCP is ModelContextProtocol (+ AspNetCore) on top of Voluta.
• No built-in coding agent (bash/edit/permissions) — Voluta is the graph runtime, not Claude Code.

Documentation

Product docs live in docs/ (product.md + version trees such as 0.x/**/*.mdx). On every v*.*.* tag the publish workflow packs them into docs.tgz (tarball root = product.md + 0.x/…, not nested under an extra docs/ folder) and attaches the asset to the GitHub Release for that tag. Public site: docs.stbl.space/voluta.

# local dry-run of the release asset layout
tar -czf docs.tgz -C docs .
tar -tzf docs.tgz | head

Development

dotnet build voluta.slnx                      # 0 warnings, 0 errors — the gate
dotnet test  voluta.slnx                      # xUnit + Shouldly + NSubstitute
dotnet format voluta.slnx --severity hidden   # style drift
dotnet run -c Release --project benchmarks/Voluta.Benchmarks

TreatWarningsAsErrors + EnforceCodeStyleInBuild are on. Specs: openspec/specs/. Agent handbook: CLAUDE.md.

Contributing

Small fixes → PR. Non-trivial changes → issue first (contracts still move).

git config core.hooksPath .githooks   # once per clone

Commit shape: [voluta](feat/scope): subject. Details: CONTRIBUTING.md.

Inspiration

Execution model from LangGraph (MIT) — supersteps, channel/reducer state, checkpoint-first persistence. The API diverges substantially; design mistakes are ours, not theirs.

License

MIT — see LICENSE.