/**
 * The ONE canonical serialization of `prd/handoff.md` frontmatter.
 *
 * the handoff capsule is written by two producers and read by four
 * consumers, and they did not agree on the bytes:
 *
 *   | consumer / producer | requirement |
 *   |---|---|
 *   | `AUDIT_REQUIRES_HANDOFF` (`artifact-prerequisites.ts`) | SUBSTRING `schemaVersion: 2` (unquoted) + `sha256:` |
 *   | `audit-independent/{security,perf}-audit-service.ts` | anchored `^schemaVersion:\s*(\d+)\s*$` and `^sha256:\s*([a-f0-9]{64})\s*$` |
 *   | `handoff-service.readHandoff` | YAML string `handoffHash` |
 *   | `handoff-service.verifyHandoff` | `handoffHash` === sha256(body), bare hex |
 *
 * `handoff-service.serializeHandoff` fed the frontmatter through
 * `yaml.stringify`, which emits `schemaVersion: "2"` and a bare
 * `handoffHash:` — failing the gate AND both loaders. `handoff-auto-regen.ts`
 * hand-rolled a second serialization that happened to satisfy all four. Two
 * producers, two facts about the same contract, one of them wrong: that is
 * the defect, and copying the right shape into a third place would keep it.
 *
 * So both producers call THIS function. `sha256` is emitted only here, and
 * it is emitted plain, because the two audit loaders anchor a regex on it.
 *
 * Scalar-quoting rule — one rule, one documented exception set:
 *   - every ordinary string is emitted through `yamlScalar` (a JSON
 *     double-quoted scalar, which is valid YAML 1.2 and round-trips
 *     backslashes correctly on Windows paths);
 *   - `schemaVersion` and `sha256` are the exception: emitted PLAIN, because
 *     they are the two scalars the gate and the loaders match textually and a
 *     quoted scalar is invisible to all three. Both values are structurally
 *     constrained (a version digit and 64 hex chars), so plain is unambiguous.
 *
 * `handoffHash` is quoted even though it is also a 64-hex value: the reader
 * parses the block through YAML and requires a STRING, and a bare all-digit
 * sha256 would parse as a YAML number and be refused by the shape check.
 */
import { type HandoffFrontmatter } from './handoff-types.js';
/**
 * Serialize `frontmatter` into the fenced block, terminated by the closing
 * `---` and a trailing newline. Callers append the body verbatim, which keeps
 * the sha256 of the body independent of how the frontmatter renders.
 */
export declare function serializeHandoffFrontmatter(frontmatter: HandoffFrontmatter): string;