Support · Recommended implementations & strategies

Shared contracts & helpers

Open group

Symbol	Kind	Purpose
agent	function	Instantiate an Engine configuration class without creating an Engine, budget or request.
Agent	type	Original Engine configuration; union branches retain their required App/model relationships.
AgentOptions	type	Agent id is an external pool identity, not an override of Core branch or request identity.
agentPool	constant
AssociatedRegistration	interface	Owners retain their business fields; Support only reads model interface associations.
AssociationOptions	interface	Shared independent tools and a default projection from existing contracts.
AssociationSource	interface	Local provenance, never an extra model input requirement.
ClassDecoration	type
DecorationOptions	interface	Namespaces group external registration without changing Core options.
defineAssociatedCatalog	function	Compile independent and owner-derived Tool declarations, validating all references eagerly.
DefinitionReader	interface	Read-only roots. A typed read describes the expected contract, not a static id/type lookup.
fragment	function	Instantiate a self-describing fragment class; the original builder owns formatting checks. Bind a host's formatter method into an original fragment configuration.
Fragment	type	A formatter and its original provenance, trust and budget configuration.
fragmentPool	constant
IdentifiedDefinition	interface	Registration identity; ids are unique within one kind and namespace.
Intent	function	Mark a WorkflowTool for demand discovery; alone this decorator registers nothing.
MethodDecoration	type
model	function	Instantiate and validate model options without creating a Runner or consuming calls.
Model	type	Original Runner configuration; the decorator's pool id is not a model identity override.
ModelOptions	type	Model id is only a pool key; Core still owns the configured model/transport identities.
modelPool	constant
node	function	Instantiate a node definition class once, injecting its id; graph validation stays in Workflow. Bind a named host method as run without renaming or manually binding the original object.
Node	type	A node implementation; its public id is supplied by
nodePool	constant
Support	namespace
tool	function	Instantiate a tool definition class; schema and authorization stay with existing defineTool. Bind an existing host method as the tool's execute callback. A model-only tool method provides its synchronous resolver.
Tool	type	A tool implementation with the original schema, authorization and execution contracts.
ToolAssociation	type	Explicit tool references or inline overrides of the owner's default model interface.
toolPool	constant
workflow	function	Instantiate and validate workflow options, leaving actual execution with the original Engine.
Workflow	type	A complete graph definition whose workflow id is supplied by
workflowPool	constant

Tools & capabilities

Open group

Symbol	Kind	Purpose
CapabilityCatalogOptions	interface	Catalog construction options.
CapabilityModule	interface	Minimal composition contract; lifecycle and domain fields remain application-owned.
CapabilityToolReferences	interface	Tool references declared by one owner module.
CompiledTool	type	Tool definition type derived from a declaration literal, preserving input/output/id.
defineCapabilityCatalog	function	Build a frozen capability catalog from application module declarations. Each module must carry a non-empty description, and every contributed tool ID must be unique across modules. Reference projections run during construction and must be synchronous.
defineTool	function	Validate one tool declaration and freeze a detached copy of it. authorize must settle with void; a rejection has to be thrown, so a returned false cannot silently pass. Handlers are bound to the declaration object, and the input schema is re-snapshotted so later mutation cannot widen the accepted input.
defineToolCatalog	function	Infer the host context from existing executable definitions, without widening it to unknown. Explicit host typing remains available for contextually typed declaration lists.
SelectedTools	type	Catalog narrowed to the given ids: each kept tool's id literal is intersected with Id.
ToolCatalog	interface	Frozen tool catalog with model tools and per-request binding.
ToolCatalogEntry	type	Public declaration surface of one tool, without registry internals.
ToolModelView	interface	Model capability view of a tool catalog, retaining the host context type.
ToolOutput	type	Output type of the tool whose id matches Id; never for any other id.
ToolRuntime	interface	Catalog bound to one App request.
validateToolReferences	function	Validate tool references against the complete registered set. Checking against every registered tool (not only the ones available in the current request) keeps the declaration honest: a module may reference a tool that this request filters out, but never one that does not exist.

Models & interaction

Open group

Symbol	Kind	Purpose
chatCompletionFunctionOptions	function	Build the tool-selection request fields for a function-calling stage. The adapter expects exactly one function call per response, so tool use is required and parallel calls are disabled.
chatCompletionMessages	function	Map Core and provider messages to chat-completions message payloads. Only declared message fields are sent. Assistant tool declarations become nested tool_calls, and tool results become tool_call_id; both are rewritten explicitly rather than forwarded as-is. Messages with images become a content-block array; images are accepted only on user messages and only as http(s) or data:image URLs.
chatCompletionParts	function	Convert one streamed choice.delta into Core model parts. Text is emitted only when non-empty; each tool-call fragment carries its index so Core can reassemble arguments that arrive across chunks.
CompatibleModelConfig	interface	Configuration of one OpenAI-compatible endpoint.
CompatibleModelPorts	interface	Adapter ports the App may override without replacing the provider.
CompatibleModelProvider	class	HTTP/SSE lifecycle shared by hosts. Apps supply config and user-visible error mapping only. A static configuration is validated and frozen in the constructor. A configuration function is called once per request instead, so credentials and models may rotate between calls.
CompatibleModelProviderOptions	interface	Construction options for a compatible provider.
CompletionFailure	type	Build the classified failure a policy throws; the provider records it like its own failures.
CompletionPolicy	interface	Decision whether a finished stream satisfies the request.
completionPolicyCatalog	constant
CompletionRequestFacts	interface	Facts the provider reads from the request it actually sends. functions reports the Core call options and keeps the default policy equivalent to the behavior that existed before policies were configurable. toolChoice is the effective field of the serialized body, so a host override, or a field dropped for being undefined, is visible exactly as the upstream receives it.
CompletionSession	interface	Per-request completion state observed by one policy.
createJsonTransport	function	Create a typed JSON transport without a capability-selection envelope. The transport embeds the JSON Schema in the instruction and requires the response to be one complete JSON value. The returned response parser rejects native call events and invalid JSON, then validates the value through the supplied schema.
createModelStrategy	function	Compose runner options in precedence order: budget preset, selected model, declared reasoning, exact budget, then explicit Core fields. The result is validated through the same Core binding rules but creates no runner and spends no calls.
createProviderObservationScope	function	Bind provider observations to a caller-owned destination across diagnostic child spans. attach returns a scoped diagnostic context; contexts that were not attached through this scope produce no observations. Child contexts inherit the owner and a parent/child span path.
createReplyPreview	function	Create a model-output event handler that publishes preview bubbles. The handler resets on model.start, ignores other invocations, disables itself on unexpected output, and clears the preview when a call ends unsuccessfully. Rules are snapshotted at creation, and only explicitly registered prose fields are projected.
createReplyPreviewRules	function	Generate frozen preview rules from capability and stage declarations. Capabilities without preview metadata are skipped even when their stage opts in. Default paths are text and bubbles[*], each kept only when the capability schema declares it.
createSessionModelTransport	function	Create a session transport.
createStageModelTransport	function	Build a transport that projects a capability source through declared stage references.
createTextTransport	function	Create a plain-text transport that trims the assembled response.
defaultCompletionPolicy	constant
defineModelTools	function	Build a sealed capability catalog from typed declarations.
modelBudgetStrategies	constant
ModelBudgetStrategy	type	Preset name, or an explicit partial set of Core runner settings.
ModelChildrenOptions	interface	Group options: worker count, extra cancellation and accept/commit hooks.
ModelChildTask	interface	One child call in a group: its own limits plus the work to run with the child runner.
ModelChoiceIndex	interface	Minimal selector shape used while filtering the provider response choices.
modelInteractionCatalog	constant
ModelProviderErrorCode	type	Stable failure classification reported by the compatible provider adapter.
ModelProviderFailure	interface	Failure detail passed to the App's error factory.
ModelStageTransportRegistration	interface	Stage IDs and capability references are App-owned; this adapter only compiles their relation.
ModelStrategyOptions	type	Input of createModelStrategy: model selection, optional reasoning and budget plus explicit Core overrides. Explicit Core fields win over every generated value.
PreparedSessionTransport	interface	Prepared session transport handed to the runner.
prepareSessionFunctions	function	Build the session policy for one stage.
PreviewTool	interface	A model tool with an explicit, presentation-only streaming preview contract.
ProviderAssistantMessage	interface	Assistant turn; content may be empty when the turn is only a tool declaration.
ProviderErrorCapture	interface	Captured upstream error body and whether it had to be truncated.
ProviderEventDescriptor	interface	Provider event name plus its content class.
ProviderEventName	type	Union of provider event names.
ProviderEventPayloads	interface	Payload of each provider event. Content-bearing events are accepted explicitly.
ProviderMessage	type	Message list a host may pass to the compatible provider directly.
ProviderObservation	type	One observation: event name with its payload.
ProviderObserver	interface	The caller can correlate each observation using the original, request-local model options.
ProviderReasoningLevel	type	Supplier wire shape is explicit; levels express requested effort, not measured quality.
ProviderReasoningStrategy	type	How a reasoning level is translated into request fields. requestBody entries override generated fields, so a host can correct a provider that expects a different shape.
ProviderSystemMessage	interface	System instruction turn; text only, so the union rejects images and tool fields here.
ProviderToolCall	type	One tool call the assistant declared, in wire order; aliases the Core shape.
ProviderToolMessage	interface	Tool result answering one declared call.
ProviderUserMessage	interface	User turn; the only message type that may carry images, and never tool calls.
ReplyPreviewOptions	interface	Settings for createReplyPreview; sink receives every bubble list and is required.
ReplyPreviewRule	interface	One projection rule: which stage/capability it matches and which prose fields may be shown. A rule without toolId may only match a registered plain-text stage.
ReplyPreviewStage	interface	Stage declaration: which tools it exposes and whether it previews text or arguments.
ReplyPreviewTool	interface	Capability declaration used to derive preview rules. Omitted preview means the capability never previews, so previewing is an explicit opt-in.
ResolvedSessionCall	interface	One completed call with host-facing resolution; unknown tools and bad JSON stay non-fatal.
ResolvedSessionResult	interface	Complete result of one session response after host-facing resolution.
runChildren	function	Run child tasks concurrently and return their values in declaration order. The first failure aborts the remaining group, but an already in-flight commit is still awaited because cancellation does not mean the write was rolled back.
sessionCompletionPolicy	constant
SessionFunctionOptions	interface	Options a session transport may pass through to provider options.
SessionModelTransportRegistration	interface	Registration for one session transport.

Context & journals

Open group

Symbol	Kind	Purpose
ContextAssemblyOptions	interface	Assembly options for placement-based projections.
ContextBuilder	interface	Compiled builder. It holds no request state and may be shared across invocations.
ContextBuilderOptions	interface	Shared builder options.
ContextCompressionCall	interface	One compression request.
ContextCompressor	interface	Registered compressor handler.
ContextFragmentConfig	interface	Self-describing fragment declaration: metadata plus a formatter.
contextHandlerCalls	function
ContextHandlerReference	interface	Reference to a registered compressor or selector handler.
ContextHistoryGrouping	type	How a message history is split into groups for trimming.
contextHistoryStrategies	constant
ContextModelCall	interface	Same runner and same fixed invocation result as public model calls.
ContextModelRequest	interface	One model call made on behalf of a selector or compressor.
ContextNodeResult	interface	Outcome of one context node: the built input, its prepared model call and the change report.
ContextPolicy	type	Declared context policy for one stage.
contextPolicyCatalog	constant
ContextProcessingNodeDefinition	type	Definition accepted by createContextProcessingNode. It is a normal Core WorkflowNode except that the node body is declared here: plan builds the context, update decides the committed state, and policy/handlers/timeout are validated when the node is created.
ContextProcessingOptions	interface	Runtime inputs for one processing run.
ContextProcessingReport	interface	Facts recorded for one processing run.
ContextProjection	type	One declared projection: a single fragment or a placement expanded into fragments.
ContextRecentHistory	interface	Recent history that compression must keep verbatim.
ContextReduction	type	One declared reduction step.
contextReductionCatalog	constant
ContextReductionNodeDefinition	type	Definition of a reduction node: one registered step is applied per node run. stepId may be fixed or derived from state, which lets a graph route over several steps.
ContextSelection	type	Selection is independent of ownership; omitted selection preserves ordered execution.
ContextSelectionCall	interface	Everything a selector may inspect for one decision.
ContextSelectionCandidate	interface	Candidate step considered by selection, with its measured cost.
contextSelectionCatalog	constant
ContextSelectionNodeDefinition	type	Definition of a selection node: like a processing node, but update receives chosen step IDs.
ContextSelectionResult	interface	Selection stage result: the chosen step IDs plus the unchanged stage snapshot.
ContextSelector	interface	Model or local selector that chooses which reductions to apply.
ContextStageResult	interface	Result of a selection or reduction stage, before the node's update commits chosen fields.
ContextStrategy	interface	Validated inputs ready to pass to a context processing node.
ContextStrategyOptions	type	One history declaration that generates a step, or an explicit step list with optional history fields (fragment, field, preset, targetChars, keepGroups, grouping).
ContextStrategySettings	type	Shared reduce-policy settings applied to the whole strategy. Trigger and target fields follow the Core policy contract; omitted values fall back to the plan budget or to the trigger. Supplying steps disables generation and uses the explicit list.
ContextTokenMeasurement	interface	Injected token measurement for token-triggered policies.
createContextCompressor	function	Build a compressor that asks a model to rewrite one fragment. The request pairs a system instruction with a user message carrying the fragment ID, its current value and the target character count. Only the model's parsed value is returned; the caller decides whether the result fits the reduction contract.
createContextProcessingNode	function	Create one node that runs the complete context policy and returns the built context. Use this when the graph does not need to route between selection and reduction phases.
createContextReductionNode	function	Create a node that applies exactly one registered reduction step. Partial plans keep the full budget until final assembly, so intermediate nodes do not shrink the allowance reserved for the reply.
createContextSelectionNode	function	Create an ordinary node that selects reduction steps without executing them. The node reports the registered step IDs so the graph can route to reduction nodes itself.
createContextSelector	function	Build a selector that asks a model to pick reduction steps. Without a custom parser the model must answer with a JSON object containing a stepIds array; with a custom parser the application owns that contract but must still return step IDs.
createContextStrategy	function	Build a reduction policy from one or more history declarations. recent keeps a window of recent groups; continuity summarizes older groups while preserving the most recent originals. Neither preset claims semantic quality, only bounded input size.
defineContextAssembly	function	Compile ordered context projections into a builder. A projection is either a single fragment (with its own formatter) or a placement whose contribution handler expands to any number of fragments at request time.
defineContextFragments	function	Compile self-describing fragment declarations into a builder. Each definition carries its own trust, lifetime and size metadata, so no separate metadata catalog is needed. The budget may be a constant or a function of the request input.
processContext	function	Run a complete context policy in one call: snapshot, execute and finalize.
reservedContextCalls	function
selectContextSteps	function	Choose steps that fit the remaining call budget. Feasibility uses exact trim previews and declared call ceilings; the reply reserve and the selector's own allowance are subtracted before candidates are considered, so neither can be spent on reductions.
transformContextText	function	Apply a text transform to a fragment value, including strings nested inside objects. Structured values are walked through a JSON round trip, which is what the budget measurement serializes later; values that JSON cannot represent are therefore not preserved.
validateContextPolicy	function	Validate a complete context policy and every handler it can reference. Handler IDs must be unique and each handler must declare a non-negative integer call ceiling. Reduction targets and selection modes are checked by their own catalog entries.
validateContextSelection	function	Validate selector declarations and the selection mode they serve.

Configuration, catalogs & policies

Open group

Symbol	Kind	Purpose
defineRegistrationCatalog	function	Compile an ordered installation plan. Predicates observe the effects of preceding installations at request time; a predicate that throws rejects the install instead of being treated as false. Callbacks are bound to their declaring definition so implementations may rely on this.
defineSchema	function	Re-snapshot an existing adapter without changing its behavior. Used to detach a caller-owned adapter from later mutation before it is exposed or reused.
fromJsonSchema	function	Build an adapter from a caller-owned typed JSON Schema compiler. The schema is cloned and frozen before it reaches the compiler, so later mutation of the input cannot change validation. Compilation and validation must both be synchronous.
fromParserSchema	function	Wrap a library schema that already parses values (for example Zod or Valibot style). parse is delegated unchanged, so the library keeps ownership of coercion and error reporting; only the JSON Schema projection is produced here.
JsonSchemaOptions	interface	Options for building an adapter from a JSON Schema compiler.
JsonSchemaValidator	interface	App-owned JSON Schema compilers provide synchronous validation.
RegistrationDefinition	interface	One install step.

Transport & streaming

Open group

Symbol	Kind	Purpose
encodeSseEvent	function	Encode one event in the server-sent events wire format. Every line of data gets its own data: field, because a raw newline would start a new field.
JsonFrameLimits	interface	Bounds applied while scanning a streamed text.
JsonTransportPart	type	One scanned span: a complete object frame or a character outside any frame.
parseJsonFrames	function	Parse complete object frames under explicit count and size limits. Only whitespace may appear outside frames; a stray closing brace is tolerated only up to maxExtraClosings, which covers transports that repeat the delimiter after the payload.
scanJsonObjectFrames	function	Extract complete object-shaped spans from surrounding text, without parsing or selecting them.
SseOutputEvent	interface	One outbound event before wire encoding.
SseWriter	interface	Destination that reports backpressure instead of buffering without bound.
writeSseFrame	function	Write one encoded frame and wait for drain when the writer reports backpressure. The signal is re-checked around the write and the drain wait, so cancellation does not leave a pending write considered successful.

Observation & diagnostics

Open group

Symbol	Kind	Purpose
streamEvents	function	Bridge a push-style producer to a pull-style async iterable with a one-slot rendezvous. The producer must await every emit call before emitting again; concurrent emissions are rejected rather than buffered. The slot is released only after the consumer receives the event, so backpressure is exact.