Agent

Construction helpers, builders, manifests, and runnable agents exported by the package root.

`Agent`

Access: @nylorun/harness → Agent

Creates an open agent builder from the stable identity and optional base instructions.

Name	Type	Required	Description
`options.id`	`string`	Yes	Stable programmatic agent identifier.
`options.name`	`string`	Yes	Human-readable agent name.
`options.instructions`	`string` or `readonly string[]`	No	Initial model instructions.
Returns	`AgentBuilder`	—	An open builder that accepts capabilities and middleware.

Access: @nylorun/harness → AgentBuilder

AgentBuilder stays open until a model adapter is bound. Middleware is applied in declaration order.

Method	Parameters	Returns	Description
`use(declaration)`	`CapabilityDeclaration<State>`	`this`	Adds a named capability with tools, instructions, model selection, state, or middleware.
`use(middleware)`	`StepMiddleware`	`this`	Adds middleware with a generated id.
`use(id, middleware)`	`id: string`, `middleware: StepMiddleware`	`this`	Adds middleware under an explicit stable id.
`with(adapter)`	`adapter: ModelAdapter`	`BoundAgentBuilder`	Binds the one model adapter and closes the builder to later `use()` calls.

Access: @nylorun/harness → BoundAgentBuilder

Method	Parameters	Returns	Description
`build()`	None	`BuiltAgent`	Validates the composition and returns the built agent. A successful builder returns the same instance on later calls.

Access: @nylorun/harness → BuiltAgent

Member	Type	Required	Description
`id`	`string`	Yes	Built agent identifier from its manifest.
`name`	`string`	Yes	Built agent display name from its manifest.
`middleware`	`readonly BoundMiddleware[]`	Yes	Ordered, compiled middleware declarations.
`manifest`	`AgentManifest`	Yes	Public id, name, and middleware-id manifest.
`run(options?)`	`SessionRunOptions`	No	Creates and returns an in-memory `Session`.

run() accepts either normal session options or a seeded session option. A seed cannot be combined with top-level id, userId, or context.

Access: @nylorun/harness → model, middleware, tool

Helper	Parameters	Returns	Description
`model(value)`	`ModelAdapter`	The same adapter	Preserves model-adapter inference.
`middleware(value)`	`StepMiddleware`	The same middleware	Preserves middleware inference.
`tool(value)`	`ToolDefinition`	Prepared `ToolDefinition`	Preserves tool inference and prepares its synchronous Zod object schema.

Access: @nylorun/harness → AgentManifest, AgentBuildError, AgentLifecycleError

Export	Properties or value	Description
`AgentManifest`	`id`, `name`, `middleware`	Public description of a built agent; every middleware item contains its `id`.
`AgentBuildError`	`diagnostics: readonly BuildDiagnostic[]`	Raised when Harness cannot build a valid composition.
`AgentLifecycleError`	`code: "agent.lifecycle-sealed"`	Raised when a builder is changed after `with()` or `build()`.

Both error classes extend HarnessError. Use their machine-readable code instead of matching the message text.