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https://github.com/agentruntimecontrolprotocol/php-sdk

PHP reference SDK for ARCP (Agent Runtime Control Protocol).
https://github.com/agentruntimecontrolprotocol/php-sdk

agent-protocol agent-runtime-control-protocol agents ai-agents arcp durable-execution llm mcp php sdk streaming

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PHP reference SDK for ARCP (Agent Runtime Control Protocol).

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README 

          
ARCP PHP SDK



PHP SDK for the Agent Runtime Control Protocol (ARCP) — submit, observe, and control long-running agent jobs from PHP.





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  Specification ·

  Concepts ·

  Install ·

  Quick start ·

  Guides ·

  API reference




---



`arcp/sdk` is the PHP reference implementation of [ARCP](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md), the Agent Runtime Control Protocol. It covers both sides of the wire — `Arcp\Client\ARCPClient` for submitting and observing jobs, `Arcp\Runtime\ARCPRuntime` for hosting agents — so either side can talk to any conformant peer in any language without hand-rolling the envelope, sequencing, or lease enforcement.



ARCP itself is a transport-agnostic wire protocol for long-running AI agent jobs. It owns the parts of agent infrastructure that don't change between products — sessions, durable event streams, capability leases, budgets, resume — and stays out of the parts that do. ARCP wraps the agent function; it does not define how agents are built, how tools are exposed (that's MCP), or how telemetry is exported (that's OpenTelemetry).



## Installation



Requires PHP 8.4 or newer and Composer 2.x. The SDK ships as a single Composer package; the `bin/arcp` CLI is registered automatically so `vendor/bin/arcp` is available in any project that pulls it in.



```sh

composer require arcp/sdk

```



The `pdo_sqlite`, `mbstring`, and `json` extensions are required (all bundled with most PHP distributions). The runtime uses [Amp v3](https://amphp.org/) + fibers; no extra extension is needed for async.



## Quick start



Connect to a runtime, submit a job, stream its events to completion:



```php

open(

    Auth::bearer((string) getenv('ARCP_TOKEN')),

    new PeerInfo('quickstart', '1.0.0'),

    new Capabilities(streaming: true, subscriptions: true),

);



$client->subscribe(

    ['types' => ['job.progress', 'log', 'metric']],

    static function (Envelope $env): void {

        if ($env->payload instanceof JobProgress) {

            printf("[progress %d%%] %s\n", $env->payload->percent, $env->payload->message ?? '');

        }

    },

);



$result = $client->invokeTool('data-analyzer', ['dataset' => 's3://example/sales.csv']);

printf("final: %s\n", json_encode($result->value));



$client->close();

```



This is the whole shape of the SDK: open a session, submit work, consume an ordered event stream, get a terminal result or error. Everything below is detail on those four moves.



## Concepts



ARCP organizes everything around four concerns — **identity**, **durability**, **authority**, and **observability** — expressed through five core objects:



- **Session** — a connection between a client and a runtime. A session carries identity (a bearer token), negotiates a feature set in a `hello`/`welcome` handshake, and is *resumable*: if the transport drops, you reconnect with a resume token and the runtime replays buffered events. Jobs outlive the session that started them. See [§6](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md).

- **Job** — one unit of agent work submitted into a session. A job has an identity, an optional idempotency key, a resolved agent version, and a lifecycle that ends in exactly one terminal state: `success`, `error`, `cancelled`, or `timed_out`. See [§7](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md).

- **Event** — the ordered, session-scoped stream a job emits: logs, thoughts, tool calls and results, status, metrics, artifact references, progress, and streamed result chunks. Events carry strictly monotonic sequence numbers so the stream survives reconnects gap-free. See [§8](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md).

- **Lease** — the authority a job runs under, expressed as capability grants (`fs.read`, `fs.write`, `net.fetch`, `tool.call`, `agent.delegate`, `cost.budget`, `model.use`). The runtime enforces the lease at every operation boundary; a job can never act outside it. Leases may carry a budget and an expiry, and may be subset and handed to sub-agents via delegation. See [§9](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md).

- **Subscription** — read-only attachment to a job started elsewhere (e.g. a dashboard watching a job a CLI submitted). A subscriber observes the live event stream but cannot cancel or mutate the job. Distinct from *resume*, which continues the original session and carries cancel authority. See [§7.6](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md).



The SDK models each of these as first-class objects; the rest of this README shows how.



## Guides



### Sessions and resume



Open a session, negotiate features, and reconnect transparently after a transport drop using the resume token — jobs keep running server-side while you're gone.



```php

use Amp\Websocket\Client\WebsocketHandshake;

use function Amp\Websocket\Client\connect;

use Arcp\Client\ARCPClient;

use Arcp\Envelope\Envelope;

use Arcp\Envelope\MessageCatalog;

use Arcp\Ids\MessageId;

use Arcp\Json\EnvelopeSerializer;

use Arcp\Messages\Control\Resume;

use Arcp\Messages\Session\Auth;

use Arcp\Messages\Session\Capabilities;

use Arcp\Messages\Session\PeerInfo;

use Arcp\Transport\WebSocketTransport;



$serializer = new EnvelopeSerializer(MessageCatalog::create());

$openTransport = static fn (): WebSocketTransport => new WebSocketTransport(

    connect(new WebsocketHandshake('wss://runtime.example.com/arcp')),

    $serializer,

);



$client = new ARCPClient($openTransport());

$accepted = $client->open(

    Auth::bearer((string) getenv('ARCP_TOKEN')),

    new PeerInfo('resumable', '1.0.0'),

    new Capabilities(streaming: true, durableJobs: true),

);

$sessionId = $accepted->sessionId;

$lastMessageId = null;



// ... transport drops ...



$resumed = new ARCPClient($openTransport());

$resumed->open(Auth::bearer((string) getenv('ARCP_TOKEN')), new PeerInfo('resumable', '1.0.0'), new Capabilities(streaming: true, durableJobs: true));

$resumed->session->transport->send(new Envelope(

    id: MessageId::random(),

    payload: new Resume(afterMessageId: (string) $lastMessageId, includeOpenStreams: true),

    timestamp: $resumed->clock->now(),

    sessionId: $sessionId,

));

// The runtime replays every envelope with id > $lastMessageId, then resumes live streaming.

```



### Submitting jobs



Submit a job with an agent (optionally version-pinned as `name@version`), an input, and an optional lease request, idempotency key, and runtime limit.



```php

use Arcp\Ids\IdempotencyKey;



$result = $client->invokeTool(

    tool: 'weekly-report@2.1.0',

    arguments: [

        'week' => '2026-W19',

        'lease' => ['net.fetch' => ['s3://reports/**']],

        'expires_at' => (new DateTimeImmutable('+60 seconds'))->format(DateTimeInterface::RFC3339_EXTENDED),

    ],

    deadlineSeconds: 300.0,

    idempotencyKey: new IdempotencyKey('weekly-report-2026-W19'),

);



printf("resolved value = %s\n", json_encode($result->value));

```



### Consuming events



Iterate the ordered event stream — `log`, `metric`, `event.emit`, `tool.invoke`, `tool.result`, `job.progress`, `job.result_chunk`, `artifact.ref` — and optionally acknowledge progress so the runtime can release buffered events early.



```php

use Arcp\Envelope\Envelope;

use Arcp\Messages\Execution\JobProgress;

use Arcp\Messages\Execution\ResultChunk;

use Arcp\Messages\Telemetry\EventEmit;

use Arcp\Messages\Telemetry\LogEvent;

use Arcp\Messages\Telemetry\MetricEvent;



$client->subscribe(

    ['session_id' => [(string) $client->session->sessionId]],

    static function (Envelope $env) use ($client): void {

        match (true) {

            $env->payload instanceof LogEvent      => printf("[log] %s\n", $env->payload->message),

            $env->payload instanceof MetricEvent   => printf("[metric] %s=%s %s\n", $env->payload->name, $env->payload->value, $env->payload->unit),

            $env->payload instanceof JobProgress   => printf("[progress %d%%] %s\n", $env->payload->percent, $env->payload->message ?? ''),

            $env->payload instanceof ResultChunk   => $client->resultChunks->push($env->payload),

            $env->payload instanceof EventEmit     => printf("[event] %s\n", $env->payload->eventType),

            default                                => null,

        };

    },

);

```



### Leases and budgets



Request capabilities, a budget, and an expiry; read budget-remaining metrics as they arrive; handle the runtime's enforcement decisions.



```php

use Arcp\Envelope\Envelope;

use Arcp\Errors\BudgetExhaustedException;

use Arcp\Messages\Telemetry\MetricEvent;



$client->subscribe(

    ['types' => ['metric']],

    static function (Envelope $env): void {

        if ($env->payload instanceof MetricEvent && $env->payload->name === 'cost.budget.remaining') {

            printf("budget remaining: %.2f %s\n", $env->payload->value, $env->payload->unit);

        }

    },

);



try {

    $client->invokeTool('web-research', [

        'iterations' => 8,

        'per_call_usd' => 0.30,

        'lease' => [

            'tool.call'   => ['search.*', 'fetch.*'],

            'cost.budget' => ['USD:1.00'],

            'model.use'   => ['anthropic/claude-*'],

        ],

        'expires_at' => (new DateTimeImmutable('+10 minutes'))->format(DateTimeInterface::RFC3339_EXTENDED),

    ]);

} catch (BudgetExhaustedException $e) {

    // BUDGET_EXHAUSTED / LEASE_EXPIRED are never retryable: resubmit with a fresh lease.

    fwrite(STDERR, "job ended: {$e->code()->value}\n");

}

```



### Subscribing to jobs



Attach read-only to a job submitted elsewhere and observe its live stream (with optional history replay) without cancel authority.



```php

use Arcp\Envelope\Envelope;



$listing = $observer->listJobs(['status' => ['running']], limit: 10);

$first = $listing->jobs[0] ?? null;

if ($first === null) {

    return;

}



$subscriptionId = $observer->subscribe(

    [

        'job_id' => [$first['job_id']],

        'since_message_id' => null,           // omit to start live; set for backfill

    ],

    static function (Envelope $env): void {

        printf("[seq=%s] %s\n", (string) $env->id, $env->type());

    },

);



// ... later ...

$observer->unsubscribe($subscriptionId);

```



### Error handling



Catch the typed error taxonomy and respect the `retryable` flag — `LEASE_EXPIRED` and `BUDGET_EXHAUSTED` are never retryable; a naive retry fails identically.



```php

use Arcp\Errors\ARCPException;

use Arcp\Errors\BudgetExhaustedException;

use Arcp\Errors\ErrorCode;

use Arcp\Errors\LeaseExpiredException;



try {

    $client->invokeTool('flaky');

} catch (BudgetExhaustedException | LeaseExpiredException $e) {

    throw $e; // resubmit with a fresh lease / budget instead

} catch (ARCPException $e) {

    if ($e->isRetryable()) {

        // safe to retry with backoff (e.g. UNAVAILABLE, DEADLINE_EXCEEDED, INTERNAL)

        return;

    }

    fprintf(STDERR, "fatal: %s (%s)\n", $e->code()->value, $e->getMessage());

    throw $e;

}

```



## Feature support



ARCP features this SDK negotiates during the `hello`/`welcome` handshake:



| Feature flag | Status |

|---|---|

| `heartbeat` | Supported |

| `ack` | Partial |

| `list_jobs` | Supported |

| `subscribe` | Supported |

| `lease_expires_at` | Supported |

| `cost.budget` | Supported |

| `model.use` | Supported |

| `provisioned_credentials` | Supported |

| `progress` | Supported |

| `result_chunk` | Supported |

| `agent_versions` | Supported |



## Transport



ARCP is transport-agnostic. This SDK ships a WebSocket transport (default), an stdio transport for in-process child runtimes, and an in-memory transport for tests. WebSocket is the default for networked runtimes; stdio is used for in-process child runtimes. Select one by constructing the corresponding `Arcp\Transport\Transport` implementation (`new WebSocketTransport($connection, $serializer)`, `new StdioTransport(...)`, `MemoryTransport::pair()`) and passing it to `new ARCPClient($transport)`; the bundled `bin/arcp serve --host H --port P` exposes a WebSocket runtime that mirrors the same protocol on the wire.



## API reference



Full API reference — every type, method, and event payload — is in [`docs/`](docs/).



## Versioning and compatibility



This SDK speaks **ARCP v1.1 (draft)**. The SDK follows semantic versioning independently of the protocol; the protocol version it negotiates is shown above and in `session.hello`. A runtime advertising a different ARCP MAJOR is not guaranteed compatible. Feature mismatches degrade gracefully: the effective feature set is the intersection of what the client and runtime advertise, and the SDK will not use a feature outside it.



## Contributing



See [`CONTRIBUTING.md`](CONTRIBUTING.md). Protocol questions and proposed changes belong in the [spec repository](https://github.com/agentruntimecontrolprotocol/spec); SDK bugs and feature requests belong here.



## License



Apache-2.0 — see [`LICENSE`](LICENSE).