/**
 * @fileoverview Shared skill content-hash comparator
 * @module @skillsmith/core/services/skill-content-comparison
 * @see SMI-6343 Wave 2 — repair the content-hash comparison
 *
 * A single comparison function, consumed by every "is this skill outdated"
 * reader in the codebase (`packages/mcp-server/src/tools/outdated.ts`,
 * `packages/mcp-server/src/tools/skill-updates.ts`,
 * `packages/cli/src/utils/skills-directory.ts`) so they cannot drift apart
 * on what "current" / "outdated" / "unknown" means again — exactly the class
 * of bug an adversarial review caught in SMI-6343 Wave 1, where one
 * implementation was fixed and its siblings were left broken.
 *
 * Deliberately narrow: this function only adjudicates "do these two hashes
 * agree," given whatever installed-side and registry-side hash the caller
 * already resolved (manifest-recorded hash, on-disk SHA-256, live registry
 * lookup, cached `skill_versions` row — the callers differ on where the
 * hash comes from, not on how two hashes are compared). Richer per-caller
 * diagnosis (offline, quota-exhausted, network-error, identity-mismatch,
 * etc.) is caller-specific context this function has no visibility into —
 * callers layer their own explanation on top of the `reason` this returns.
 */
/** The three possible outcomes of comparing an installed hash to a registry hash. */
export type ContentComparisonOutcome = 'current' | 'outdated' | 'unknown';
/**
 * Result of {@link compareSkillContentHashes}.
 */
export interface ContentComparisonResult {
    /** current: hashes match. outdated: hashes differ. unknown: no comparison could be made. */
    outcome: ContentComparisonOutcome;
    /**
     * Populated only when `outcome === 'unknown'` — explains why no
     * comparison could be made (missing installed hash, missing registry
     * hash, or both). Always `undefined` for `current`/`outdated`.
     */
    reason?: string;
}
/**
 * Normalize a hash value: `null`/`undefined`/non-string/blank all collapse
 * to `null` so every caller's "I don't have this" shape (a missing manifest
 * field, an absent DB row, an `undefined` API response field) is handled
 * uniformly regardless of how the caller spells "nothing here."
 */
export declare function normalizeHash(hash: string | null | undefined): string | null;
/**
 * SMI-6343 (adversarial-review fix): return the first candidate that
 * normalizes to a non-blank value, else `null`.
 *
 * Exists because a bare `a ?? b` precedence chain (the original shape at
 * both call sites) only falls through on `null`/`undefined` — a blank
 * string (`''`, whitespace-only) is neither, so `a ?? b` incorrectly
 * "wins" with a value `normalizeHash()` would itself treat as absent,
 * silently discarding a legitimate `b`. Every caller selecting between a
 * manifest's `contentHash`/`originalContentHash` (or an on-disk fallback)
 * should route through this instead of raw `??` chaining.
 */
export declare function firstNonBlankHash(...candidates: Array<string | null | undefined>): string | null;
/**
 * Compare an installed-side content hash against a registry-side content
 * hash and return a comparison outcome plus (when `unknown`) the reason no
 * comparison could be made.
 *
 * @param installedHash SHA-256 hex digest of what is actually installed —
 *   e.g. a manifest's recorded `contentHash`/`originalContentHash`, or a
 *   freshly-computed hash of the on-disk SKILL.md.
 * @param registryHash  SHA-256 hex digest of the registry's current SKILL.md
 *   content — e.g. a live `lookupSkillFromRegistry()` result's
 *   `contentHash`, or the most-recently-synced `skill_versions.content_hash`.
 */
export declare function compareSkillContentHashes(installedHash: string | null | undefined, registryHash: string | null | undefined): ContentComparisonResult;
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