/**
 * Batch signed-URL types (D0033 / W0052 M3).
 *
 * Contract shared between the API Gateway and Studio for the two batch
 * endpoints that amortise signing over many artifacts in a single round-trip:
 *
 *   POST /v1/runs/:runId/artifacts/batch/read-urls
 *   POST /v1/runs/:runId/artifacts/batch/upload-urls
 *
 * The batch shape is intentionally symmetric: request carries the set of
 * artifact types and (for per-entry layouts) the entry keys; response carries
 * signed URLs keyed by type and entry key. For bulk layouts the response key
 * is the empty string, since bulk artifacts have no entry dimension.
 *
 * Validation is all-or-nothing per AC 4 — a single malformed entry key, an
 * unknown artifact type, or a missing keys list for a per-entry type causes
 * the whole request to 400 with zero signed URLs emitted.
 *
 * @see docs/design-docs/unified-run-artifacts.md § M3
 * @see docs/decisions/D0033-unified-run-anchored-artifact-capture.md
 */
/** The empty entry-key sentinel used for bulk responses. */
export const BULK_ENTRY_KEY = "";
