/**
 * @fileoverview The single pure compatibility gate (release 2.8.0).
 *
 * One decision function the bundled and external admission paths share
 * (north-star §5.2): given the epoch a tool was compiled against
 * (`apiVersion`) and the epoch the engine implements
 * (`PLUGIN_API_VERSION`), return a `CompatibilityVerdict` — pure data.
 * The loader (Phase 2) and CLI (Phase 3) act on the verdict; this module
 * never logs, never exits, never touches the filesystem.
 *
 * Policy:
 *   - `apiVersion` omitted ⇒ **compatible** (the grace window — a tool
 *     that predates the epoch is admitted as if current).
 *   - `apiVersion === engine` ⇒ compatible.
 *   - otherwise ⇒ incompatible, carrying both integers + a human reason
 *     (future vs. past epoch).
 */
/**
 * The outcome of the compatibility gate — pure data the caller acts on.
 *
 *   - `compatible`   — admit the tool.
 *   - `incompatible` — reject; carries the declared + engine epochs and a
 *                      human-readable reason for diagnostics / logs.
 */
export type CompatibilityVerdict = {
    readonly kind: 'compatible';
} | {
    readonly kind: 'incompatible';
    readonly declared: number;
    readonly engine: number;
    readonly reason: string;
};
/**
 * Decide whether a tool declaring `apiVersion` is compatible with the
 * engine epoch.
 *
 * @param apiVersion The epoch the tool was compiled against, or
 *   `undefined` (grace window — treated as compatible).
 * @param engine The epoch the running engine implements. Defaults to
 *   `PLUGIN_API_VERSION`; overridable for tests / as-if-external probes.
 * @returns A `CompatibilityVerdict` — never throws.
 */
export declare function checkCompatibility(apiVersion: number | undefined, engine?: number): CompatibilityVerdict;
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