/**
 * Response Envelope Schema Validator
 *
 * Zero-dependency runtime validator for provider response shapes. Used at the
 * provider boundary to detect when an upstream API silently changes its
 * response envelope — the classic "field renamed at 2am, parser throws at
 * 3am" failure mode.
 *
 * Philosophy: validate the *minimum* fields each provider's parser actually
 * reads. Don't re-type the full upstream schema — that creates brittle
 * over-specification that churns every time the provider adds an optional
 * field. Only the fields we touch matter.
 *
 * Usage:
 *   validateSchema('anthropic', data, [
 *     { path: 'content', type: 'array' },
 *     { path: 'usage.input_tokens', type: 'number' },
 *     { path: 'usage.output_tokens', type: 'number' },
 *     { path: 'model', type: 'string' },
 *   ]);
 *
 * On first failure, throws SchemaDriftError. The caller (typically the
 * factory) catches it, fires the onSchemaDrift hook, and falls over to
 * another provider.
 */
export type SchemaFieldType = 'string' | 'number' | 'boolean' | 'array' | 'object' | 'string-or-null' | 'string-or-number';
export interface SchemaField {
    /**
     * Dot-separated path into the response object. Array indices not supported
     * in the path itself — use `items` to validate array element shapes.
     */
    path: string;
    type: SchemaFieldType;
    /**
     * If true, missing paths are allowed and skipped. Useful for fields that
     * are genuinely optional (e.g. stop_sequence on Anthropic).
     */
    optional?: boolean;
    /**
     * For type: 'array' — validate each element against a nested schema.
     *
     * - `shape`: a flat SchemaField[] applied to every element (all elements
     *   the same shape).
     * - `variants` + `discriminator`: discriminated union. Each element is
     *   routed by the value of `discriminator` (a field name on the element)
     *   to the matching variant schema. **Unknown discriminator values are
     *   allowed and skipped** — we want forward-compat for additive API
     *   changes (e.g. Anthropic adds a new content block type). Only *missing*
     *   discriminators or *wrong-typed* known variants trigger drift.
     */
    items?: {
        shape?: SchemaField[];
        discriminator?: string;
        variants?: Record<string, SchemaField[]>;
    };
}
/**
 * Validate a response envelope against a minimal field schema.
 * Throws SchemaDriftError on the first mismatch, with provider + path +
 * expected/actual types surfaced for observability.
 *
 * We fail fast rather than collecting all errors: the first drift is enough
 * to trigger fallback, and walking the whole schema when we're already
 * broken wastes budget.
 */
export declare function validateSchema(provider: string, data: unknown, fields: SchemaField[]): void;
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