/**
 * Schema-update strategy framework types (M12 §3a).
 *
 * The hub core detects a schema change (SchemaDelta) and dispatches it
 * through a collection's ordered strategy list. Strategies decide what
 * happens; the core only knows this interface.
 */
/** A single changed top-level property in a schema delta. */
export interface FieldChange {
    readonly field: string;
    /** True when the field's required-ness flipped. */
    readonly requiredChanged: boolean;
    /** True when the field's subschema shape changed. */
    readonly shapeChanged: boolean;
}
/** The classified difference between a stored and a freshly-derived schema. */
export interface SchemaDelta {
    readonly collection: string;
    readonly kind: 'none' | 'additive' | 'non-additive';
    /** Top-level properties present in the new schema but not the old. */
    readonly added: readonly string[];
    /** Top-level properties present in the old schema but not the new. */
    readonly removed: readonly string[];
    /** Top-level properties present in both but altered. */
    readonly changed: readonly FieldChange[];
}
/** Context handed to a strategy alongside the delta. */
export interface UpdateContext {
    readonly collection: string;
}
/** Bulk transform run by the coordinatedCutover strategy. */
export type TransformFn = (doc: Record<string, unknown>) => Record<string, unknown>;
/**
 * A strategy's verdict on a detected schema change.
 * - `allow`   — no objection; the dispatcher falls through to the next strategy.
 * - `reject`  — terminal: refuse the change; `error` is thrown at the write path.
 * - `cutover` — terminal: run a coordinated drain-barrier (handled by coordinatedCutover).
 * New terminal actions may be added without breaking existing strategies.
 */
export type UpdateDecision = {
    readonly action: 'allow';
} | {
    readonly action: 'reject';
    readonly error: Error;
} | {
    readonly action: 'cutover';
    readonly transform: TransformFn;
};
/** A pluggable schema-evolution policy. */
export interface SchemaUpdateStrategy {
    readonly name: string;
    onSchemaDelta(delta: SchemaDelta, ctx: UpdateContext): UpdateDecision | Promise<UpdateDecision>;
}