/**
 * The spec-process half of `freezeClock` (see `DefineOptions.freezeClock`).
 *
 * `freezeClock` has always pinned the BROWSER clock (`page.clock.setFixedTime`),
 * but capture specs routinely compute fixture values in the SPEC's Node process —
 * a module-level `const GENERATED_AT = new Date().toISOString()` runs before any
 * test executes, outside the browser freeze. Such a value differs between the
 * base and the head capture run (separate processes, minutes or days apart), so
 * any surface rendering it as text drifts in width and shows up in the diff as a
 * phantom computed-style change on an unrelated PR. The in-run self-check cannot
 * catch this class: both of its captures share one spec process and therefore
 * one value.
 *
 * `styleproof-map` sets `STYLEPROOF_FREEZE_SPEC_CLOCK=1` for the Playwright run
 * it spawns. Importing this module — a side effect of importing `styleproof`,
 * which a capture spec does before evaluating its own constants — then swaps
 * `globalThis.Date` for a frozen twin: zero-argument construction, `Date.now()`,
 * and bare `Date()` calls report `STYLEPROOF_CLOCK_TIME` (default
 * `DEFAULT_CLOCK_TIME`, matching the browser freeze), while explicit-argument
 * construction, `Date.parse`/`Date.UTC`, and every instance method behave
 * normally. StyleProof's own elapsed-time bookkeeping (settle windows, popup
 * deadlines, manifest stamps) reads `realNow()`, captured before the swap.
 *
 * Opt out with `STYLEPROOF_FREEZE_SPEC_CLOCK=0` on the capture command;
 * `freezeClock: false` in the spec also restores the real clock at define time.
 */
/** The default frozen instant, shared with the browser-side freeze (`DefineOptions.clockTime`). */
export declare const DEFAULT_CLOCK_TIME = "2025-01-01T00:00:00Z";
/** Wall-clock milliseconds from the real clock, immune to the spec-clock freeze. */
export declare function realNow(): number;
/**
 * Resolve whether (and at what instant) the spec-process clock should freeze:
 * `undefined` unless `STYLEPROOF_FREEZE_SPEC_CLOCK=1`; the instant comes from
 * `STYLEPROOF_CLOCK_TIME` (ISO string or epoch milliseconds), defaulting to
 * `DEFAULT_CLOCK_TIME`. An unparseable instant throws — a silently-ignored typo
 * would run the capture on the live clock while claiming determinism.
 */
export declare function resolveSpecClockFreeze(env?: NodeJS.ProcessEnv): number | undefined;
/**
 * Swap `globalThis.Date` for a pinned twin. A Proxy over the real constructor,
 * so `Date.parse`/`Date.UTC`, the prototype, and `instanceof` all keep working.
 *
 * Two deliberately different behaviours:
 * - **Identity values stay frozen**: zero-argument `new Date()` and bare
 *   `Date()` report exactly `fixedMilliseconds` — module-level fixture
 *   constants (`new Date().toISOString()`) are byte-identical across runs,
 *   which is the phantom-diff class this freeze exists to kill.
 * - **`Date.now()` advances monotonically from the frozen origin**
 *   (`fixedMilliseconds + elapsed real ms`). `now()` is the universal idiom for
 *   deadlines and elapsed-time budgets — in consumer `--setup` helpers and in
 *   Playwright's own bundled retry loops — and a `now()` that never moves turns
 *   every such bound into an infinite spin (a surface "timeout" the tool itself
 *   caused, or a hung capture). Values derived from `now()` are still pinned to
 *   the frozen EPOCH, so date/hour-level rendering stays stable across runs.
 */
export declare function installFrozenSpecClock(fixedMilliseconds: number): void;
/** Put the real `Date` back (the `freezeClock: false` opt-out path). */
export declare function restoreRealSpecClock(): void;
/** The instant the spec-process clock is currently frozen to, if it is. */
export declare function frozenSpecClockInstant(): number | undefined;