/**
 * Output-contract drift detection.
 *
 * DQL composition is intentionally unbounded freeform `ref()` between blocks.
 * The cost of that freedom: when a child block changes its output columns, a
 * parent that `ref()`s it can break *silently*. We do not restrict composition
 * — instead we make drift *visible*.
 *
 * This pass compares the columns a parent block references on a `ref()`'d child
 * (extracted from the parent's SQL) against the child's current `outputContract`
 * (its actual output schema). A referenced column that is missing/renamed
 * produces a `kind: 'drift'`, `severity: 'warning'` diagnostic naming the
 * parent, the child, and the drifted column. It never fails the build, and
 * additive changes (the child gaining new columns) produce no warning.
 *
 * Non-goals (explicitly rejected — see the feature spec):
 *   - Hard compile-time parent→child binding / failing the build.
 *   - Runtime enforcement.
 */
import type { ManifestBlock, ManifestDiagnostic } from './types.js';
/**
 * Detect output-contract drift across all blocks. For each parent block that
 * `ref()`s a child block and references one of its columns, warn when that
 * column is no longer in the child's `outputContract`.
 *
 * Conservative on every axis: unknown child schemas, unparseable parent SQL,
 * and ambiguous (multi-source, unqualified) column references all yield no
 * warning rather than a false positive — see `extractRefColumnUsage`.
 */
export declare function detectOutputDrift(blocks: Record<string, ManifestBlock>): ManifestDiagnostic[];
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