WithOutputSchema freezes one optional provider-neutral final-output policy. See Structured Output for the portable schema contract, request behavior, decoding, and validation:

func WithOutputSchema(output inference.OutputSchema) Option

The option clones the schema immediately and Define validates it with the inference package’s output-schema validator. Invalid JSON, unsupported schema shape, or an invalid structured-output policy is returned as *loop.DefinitionError{Kind: loop.DefinitionInvalidOutputSchema}. Error text does not echo raw schema bytes.

Schema ownership

The definition owns the schema. BoundDefinition.OutputSchema() returns (*inference.OutputSchema, bool); the pointer is a fresh clone. A caller can edit that returned value for local inspection without changing the definition, the runtime request policy, or the Rig fingerprint.

The schema is a final-output contract. It does not add a callable model-facing tool, does not appear in BoundDefinition.Tools(), and does not change Definition.ToolRequirements(). The runtime may use the provider-neutral structured-output control path internally, but the public definition still rejects a declared tool whose produced name is the reserved structured-output control name.

bound, err := definition.Bind(ctx, bindings)
if err != nil {
	return err
}
schema, configured := bound.OutputSchema()
if configured {
	log.Printf("final output policy %q", schema.Name)
	// schema is owned by this caller; mutating it cannot mutate bound.
}

The policy identity is a compact-schema SHA-256 projection plus the schema name and the inference structured-output revision. Whitespace-only JSON formatting does not create a different identity; changing schema meaning, name, strictness, or implementation revision does.

Output Schema

Schema ownership

Source and proof