Module capability 

Capability descriptors that constrain runtime behavior without owning graph shape.

Fragment: capability-structure-vs-boundary

Workflow shape and node capability are intentionally modeled in separate crates. The workflow model answers “what ports exist and how are they connected?”, while this module answers “what is a node allowed to receive, emit, or ask the runtime to do?” Keeping those concerns apart prevents the graph model from quietly becoming a security or isolation policy surface.

Fragment: capability-port-claims

Port capabilities are duplicated as claims instead of reusing workflow port declarations directly because they serve a different purpose. Workflow ports describe topology; capability ports describe permitted runtime behavior. The duplication is intentional even though later validation must keep the two in sync.

Fragment: capability-workflow-cross-validation

Cross-validation lives here rather than in the workflow crate because a mismatch is still fundamentally a capability problem: the workflow only promises that a port exists, while this module decides whether a node’s declared permissions line up with that topology. The validator therefore consumes a WorkflowDefinition as read-only structure and keeps the capability error vocabulary as the single place callers inspect.

Fragment: capability-effect-taxonomy

The current EffectCapability enum is intentionally modest and concrete. It names host effects the runtime can plausibly mediate today without pretending that native nodes are sandboxed. For native execution these capabilities are advisory metadata; for future WASM or process-backed nodes they become part of a real enforcement boundary. Observability concerns such as logging, tracing, and metadata collection are deliberately excluded unless a node asks the host to write to an external sink; routine runtime telemetry belongs to the metadata layer.

Structs

NodeCapabilities

Validated capability descriptor for one node.

PortCapability

A named claim that a node may use a port in one direction.

Enums

CapabilityValidationError

Validation error for node capability descriptors.

EffectCapability

External effect a node may request from the runtime boundary.

PortCapabilityDirection

Direction of message flow a node claims for a port.

Functions

validate_workflow_capabilities

Validate that node capability descriptors align with one workflow topology.