Skip to main content
Version: 0.1.0-alpha.4 (alpha)

Contracts and bindings

The current node validates component metadata and dispatches supported exported contracts/functions through the generic Wasmtime backend. Verified package association and bounded release/runtime comparison accompany execution. The host ABI, sealed capability broker and host/local binding compiler preserve exact contracts. Isolated local calls execute through a separate child activation. Remote calls, inline composition and automatic contract migration are not implemented.

Contract authority​

WIT is authoritative for capsule-visible types, functions, resources, futures, streams, imports, and exports. Language SDK surfaces are generated or handwritten projections and must not change semantics.

Version identity​

A release has separate identities for:

  • implementation semantic version,
  • release content digest,
  • exported contract versions,
  • imported contract requirements,
  • minimum fabric version.

Implementation version and contract version are not interchangeable.

Binding graph​

A binding connects one consumer import to one provider export or host capability:

consumer revision + imported contract + caller policy
    → binding
    → host capability | local provider | remote provider | derived composition

Physical modes​

  • host: import is supplied by the capability broker.
  • inline: planned composition in the same activation; compilation is rejected today.
  • isolated-local: selects an exact local target and dispatches a separately admitted child activation.
  • remote: planned calls to another node; compilation is rejected today.
  • auto: compiler selects one unambiguous installed provider within explicit allowed modes.

Inline eligibility​

Inline composition requires compatible trust, state, transaction, budget, and observability semantics. A deployment may forbid inline mode even when technically possible.

Error semantics​

Domain errors remain declared by WIT. Fabric errors use the platform-error envelope. Generated clients must expose both layers and must not make isolated or remote calls appear infallible.

Compatibility direction​

Compatibility checks consider removed functions, changed parameter/result types, changed variant cases, resource semantics, async behavior, and transitive package dependencies. Breaking contracts require a new major contract version and explicit migration or parallel routing.

Current preparation checks agreement between the supplied manifest/contract metadata and actual component imports, exports and supported value signatures. Bounded release comparison uses the exact pinned WIT definitions of checked packages, plus actual-node runtime requirements. Descriptor-only analysis cannot establish named record or variant structure. Unsupported and unknown results deny compatibility approval; general WIT migration remains future work. Exact host/local binding compilation uses these checked definitions and rejects unsupported or ambiguous inputs. WIT versions remain distinct from workspace and SDK package release versions.