/**
 * Stable content hash for a Sanity document, used to decide whether the
 * cached AI brief is still valid for this doc.
 *
 * "Same hash" must mean: nothing the LLM brief endpoint cared about has
 * changed. Things that DON'T affect the brief (and so are stripped):
 *   - `_rev` / `_updatedAt` / `_createdAt` — change on every save, no
 *     semantic meaning to the brief.
 *   - `_id`, `_key` — identity, not content.
 *   - Bare references (`{_type:'reference',_ref:...}`) — opaque pointers;
 *     the server can't fetch them without a separate query, so they don't
 *     contribute to the brief.
 *
 * Things that DO matter (and so are kept):
 *   - title, description, body text, plain field values
 *   - portable text (flattened to plain strings, the same way the server
 *     does it in `compactDocForPrompt`)
 *
 * The hash itself is djb2 (xor variant) → 32-bit unsigned → hex. Not
 * cryptographic — we only need stable equality detection for cache lookups.
 * This stays in 8 hex chars max. Browser-safe, no crypto.subtle dependency.
 */
/**
 * Compute a stable hash of the brief-relevant content of a Sanity doc.
 * Returns a stable hex string; `null` when the input isn't a usable doc.
 *
 * Same doc → same hash. `_rev`/`_updatedAt` changes alone → same hash.
 * Title or body change → different hash.
 */
export declare function hashDocForBrief(doc: unknown): string | null;