/**
 * Production build identifier — written by `nexus build` to `.nexus/build-id.json`.
 * Server and browser must agree on this value so stale tabs can be rejected with 412.
 */
/**
 * Reads `.nexus/build-id.json` once and caches the result.
 * Returns `null` if the file is missing (dev without prior build, or legacy deploy).
 */
export declare function loadAndCacheNexusBuildId(appRoot: string): string | null;
/** Cached build id after {@link loadAndCacheNexusBuildId}; `null` if none loaded. */
export declare function getExpectedNexusBuildId(): string | null;
/** Test hook */
export declare function resetNexusBuildIdCache(): void;
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