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Vega
Vega Capability Protocol

Communication

Current VCP communication is a direct Python Runtime-to-Provider contract. No public transport, request envelope, response envelope, streaming endpoint, or heartbeat protocol exists.

Concepts

  • Initialization context: Provider-scoped, read-only services supplied to initialize.
  • Execution request: immutable action identity, inputs, deadline, and optional Runtime correlation data.
  • Execution context: per-execution cancellation, progress, services, and leases.
  • Progress callback: an async callback installed by the Runtime.
  • Result: the successful return value from execute.

Direct call flow

sequence
Runtime → Provider : initialize(ProviderInitializationContext)
Runtime → Provider : health_check()
Runtime → Provider : execute(CapabilityExecutionRequest, CapabilityExecutionContext)
Provider → Runtime : ProgressReporter callback (zero or more)
Provider → Runtime : CapabilityExecutionResult or CapabilityError
Runtime → Provider : shutdown()

CapabilityExecutionContext.validate_request MUST succeed before a Provider uses a request. ProgressReporter.report freezes the payload, applies its configured size limit, validates it when a callback is configured, and emits an event dictionary with execution_id, increasing sequence, UTC timestamp, trace_id, and payload to the Runtime callback.

Progress example

python
await context.progress.report({"phase": "synthesizing", "percentComplete": 10})

The payload itself MUST meet the Action progress schema when the Runtime injects schema validation. The SDK does not expose that callback as a remote event wire format.

Cancellation and deadlines

The Runtime requests cooperative cancellation through context.cancellation. The Provider SHOULD use raise_if_cancelled at safe points and MAY wait for the token. An Action may declare cancellation support; a Provider may also implement the optional cancel(execution_id) method. A deadline is visible in the request and context, but the SDK does not autonomously cancel at the deadline.

Runtime
→
CancellationToken
→
Provider safe interruption point
→
Underlying stop attempt
→
Result or CancellationCapabilityError

Python SDK example

python
class EchoProvider(BaseCapabilityProvider):
    async def on_execute(self, request, context):
        context.validate_request(request)
        context.cancellation.raise_if_cancelled()
        await context.progress.report({"phase": "working"})
        return CapabilityExecutionResult(output={"echo": request.inputs})

There is no TypeScript SDK or TypeScript transport example in the repository. Implementations in other languages require a separately published language-neutral VCP specification.