sanderling/pkg/spec/src/web-runtime.ts

/// <reference lib="dom" />

// V8-side runtime for `sanderling test --platform web`.
//
// The user spec is bundled with this file as the first import so that
// globalThis.__sanderling__ is installed before the spec evaluates. The host
// invokes window.__sanderlingExtractors__() and window.__sanderlingNextAction__()
// over CDP each tick. LTL predicates are intentionally stubbed: properties
// run host-side in goja, which loads its own bundle of the same spec.
//
// Element references never cross V8/host. Action targets that reference an
// AccessibilityElement collapse to `{x, y}` from getBoundingClientRect()
// before serialization.

interface Handle {
  current: unknown;
  previous: unknown;
}

interface ExtractorEntry {
  getter: (state: unknown) => unknown;
  handle: Handle;
  name: string;
}

interface ActionGeneratorHandle {
  __sanderlingActionGenerator: true;
  __sanderlingKind: string;
  generate?: () => unknown;
  entries?: readonly [number, ActionGeneratorHandle][];
}

const extractors: ExtractorEntry[] = [];
let actionsRoot: ActionGeneratorHandle | null = null;

// Deterministic PRNG so `sanderling test --platform web --seed N` is
// reproducible. The host computes a 64-bit seed and injects it via the bundle
// define SANDERLING_SEED; web-runtime reads it at init. Bit-identical parity
// with the goja PCG stream is deliberately out of scope here: this only
// guarantees same-seed -> same-run on web.
function deriveSeed32(raw: string | undefined): number {
  if (!raw) return 0;
  // Why: a 64-bit seed loses precision as a JS Number, so fold it to 32 bits
  // off the decimal string without ever materializing the full value.
  let hash = 0;
  for (let index = 0; index < raw.length; index++) {
    hash = (Math.imul(hash, 31) + raw.charCodeAt(index)) | 0;
  }
  return hash >>> 0;
}

// mulberry32: a small, well-known 32-bit PRNG. Returns a float in [0, 1).
function mulberry32(seed: number): () => number {
  let state = seed >>> 0;
  return function next(): number {
    state = (state + 0x6d2b79f5) | 0;
    let t = state;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

// esbuild Define replaces the exact member expression `process.env.SANDERLING_SEED`
// with the host-injected seed string at bundle time. When unset (e.g. the
// bundler unit tests or a non-test eval) it stays undefined and the seed is 0.
function injectedSeed(): string | undefined {
  try {
    return process.env.SANDERLING_SEED;
  } catch {
    return undefined;
  }
}

const seededRandomValue = mulberry32(deriveSeed32(injectedSeed()));

function random(): number {
  return seededRandomValue();
}

function noopFormula(): unknown {
  const formula: Record<string, unknown> = { __sanderlingFormula: true };
  formula.implies = () => formula;
  formula.or = () => formula;
  formula.and = () => formula;
  formula.not = () => formula;
  formula.within = () => formula;
  return formula;
}

const KNOWN_KEY_TO_CSS: Record<string, (value: string) => string> = {
  id: (v) => `[id="${cssEscape(v)}"]`,
  "resource-id": (v) => `[id="${cssEscape(v)}"]`,
  testTag: (v) => `[data-testid="${cssEscape(v)}"]`,
  testID: (v) => `[data-testid="${cssEscape(v)}"]`,
  "data-testid": (v) => `[data-testid="${cssEscape(v)}"]`,
  className: (v) => `[class~="${cssEscape(v)}"]`,
  class: (v) => `[class~="${cssEscape(v)}"]`,
  tag: tagSelector,
  "aria-label": (v) => `[aria-label="${cssEscape(v)}"]`,
  ariaLabel: (v) => `[aria-label="${cssEscape(v)}"]`,
  accessibilityLabel: (v) => `[aria-label="${cssEscape(v)}"]`,
  contentDescription: (v) => `[aria-label="${cssEscape(v)}"]`,
  "content-desc": (v) => `[aria-label="${cssEscape(v)}"]`,
  label: (v) => `[aria-label="${cssEscape(v)}"]`,
  placeholder: (v) => `[placeholder="${cssEscape(v)}"]`,
  placeholderValue: (v) => `[placeholder="${cssEscape(v)}"]`,
  hintText: (v) => `[placeholder="${cssEscape(v)}"]`,
};

// cssEscape delegates to the platform CSS.escape (per CSSOM spec). It produces
// output safe for both identifier and string contexts, since CSS string
// literals accept the same `\HEX ` and `\X` escape sequences as identifiers.
function cssEscape(value: string): string {
  return CSS.escape(value);
}

const TAG_NAME = /^[a-zA-Z][a-zA-Z0-9-]*$/;

// tagSelector accepts only valid HTML tag-name characters. Anything else (a
// pseudo-class like `*:hover`, a comma, whitespace) would inject CSS into the
// surrounding selector. Returning a never-matching selector rather than
// throwing keeps the spec running while making the typo visible in logs.
function tagSelector(value: string): string {
  if (!TAG_NAME.test(value)) return ":not(*)";
  return value;
}

function selectorFromObject(selector: Record<string, string | boolean | undefined>): {
  css?: string;
  xpath?: string;
} {
  const parts: string[] = [];
  let textValue: string | undefined;
  let descPrefix: string | undefined;
  for (const key of Object.keys(selector)) {
    const raw = selector[key];
    if (raw === undefined) continue;
    const value = typeof raw === "boolean" ? String(raw) : raw;
    if (key === "text") {
      textValue = value;
      continue;
    }
    if (key === "descPrefix") {
      descPrefix = value;
      continue;
    }
    const builder = KNOWN_KEY_TO_CSS[key];
    if (builder) {
      parts.push(builder(value));
    } else {
      parts.push(`[${key}="${cssEscape(value)}"]`);
    }
  }
  if (descPrefix !== undefined) {
    parts.push(`[aria-label^="${cssEscape(descPrefix)}"]`);
  }
  if (textValue !== undefined && parts.length === 0) {
    return {
      xpath: `//*[normalize-space(text())=${xpathStringLiteral(textValue)}]`,
    };
  }
  return { css: parts.join("") };
}

// xpathStringLiteral wraps the value in a valid XPath 1.0 string literal.
// XPath 1.0 has no escape syntax, so a value containing both ' and " must be
// composed via concat().
function xpathStringLiteral(value: string): string {
  if (!value.includes('"')) return `"${value}"`;
  if (!value.includes("'")) return `'${value}'`;
  const parts = value.split('"');
  return `concat(${parts.map((p) => `"${p}"`).join(`, '"', `)})`;
}

function selectorFromString(selector: string): { css?: string; xpath?: string } {
  const colon = selector.indexOf(":");
  if (colon <= 0) {
    return { css: selector };
  }
  const kind = selector.slice(0, colon);
  const value = selector.slice(colon + 1);
  if (kind === "text") {
    return { xpath: `//*[normalize-space(text())=${xpathStringLiteral(value)}]` };
  }
  if (kind === "descPrefix") {
    return { css: `[aria-label^="${cssEscape(value)}"]` };
  }
  return selectorFromObject({ [kind]: value });
}

function queryElement(
  root: ParentNode,
  selector: unknown,
): Element | null {
  if (typeof selector === "string") {
    const { css, xpath } = selectorFromString(selector);
    if (css) return root.querySelector(css);
    if (xpath) {
      const result = document.evaluate(
        xpath,
        root as Node,
        null,
        XPathResult.FIRST_ORDERED_NODE_TYPE,
        null,
      );
      return result.singleNodeValue as Element | null;
    }
    return null;
  }
  if (Array.isArray(selector)) {
    let node: ParentNode | null = root;
    for (const segment of selector) {
      if (!node) return null;
      const next = queryElement(node, segment);
      if (!next) return null;
      node = next;
    }
    return node as Element;
  }
  if (selector && typeof selector === "object") {
    const { css, xpath } = selectorFromObject(selector as Record<string, string | boolean | undefined>);
    if (css) return root.querySelector(css);
    if (xpath) {
      const result = document.evaluate(
        xpath,
        root as Node,
        null,
        XPathResult.FIRST_ORDERED_NODE_TYPE,
        null,
      );
      return result.singleNodeValue as Element | null;
    }
  }
  return null;
}

function queryAllElements(root: ParentNode, selector: unknown): Element[] {
  if (typeof selector === "string") {
    const { css, xpath } = selectorFromString(selector);
    if (css) return Array.from(root.querySelectorAll(css));
    if (xpath) return evaluateXPathAll(xpath, root as Node);
    return [];
  }
  if (selector && typeof selector === "object" && !Array.isArray(selector)) {
    const { css, xpath } = selectorFromObject(selector as Record<string, string | boolean | undefined>);
    if (css) return Array.from(root.querySelectorAll(css));
    if (xpath) return evaluateXPathAll(xpath, root as Node);
  }
  return [];
}

function evaluateXPathAll(xpath: string, root: Node): Element[] {
  const result = document.evaluate(
    xpath,
    root,
    null,
    XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,
    null,
  );
  const out: Element[] = [];
  for (let i = 0; i < result.snapshotLength; i++) {
    const node = result.snapshotItem(i);
    if (node) out.push(node as Element);
  }
  return out;
}

function elementHandle(element: Element): Record<string, unknown> {
  const rect = element.getBoundingClientRect();
  const x = Math.round(rect.left + rect.width / 2);
  const y = Math.round(rect.top + rect.height / 2);
  const ariaLabel = element.getAttribute("aria-label") ?? "";
  const text = (element.textContent ?? "").trim().slice(0, 200);
  const datasetCopy: Record<string, string> = {};
  const dataset = (element as HTMLElement).dataset ?? {};
  for (const key of Object.keys(dataset)) {
    const value = (dataset as Record<string, string | undefined>)[key];
    if (value !== undefined) datasetCopy[key] = value;
  }
  return {
    id: element.id,
    text,
    desc: ariaLabel,
    class: (element as HTMLElement).className ?? "",
    clickable: true,
    enabled: !(element as HTMLButtonElement).disabled,
    focused: document.activeElement === element,
    x,
    y,
    bounds: {
      left: Math.round(rect.left),
      top: Math.round(rect.top),
      right: Math.round(rect.right),
      bottom: Math.round(rect.bottom),
    },
    attrs: {
      tag: element.tagName.toLowerCase(),
      "aria-label": ariaLabel,
      ...datasetCopy,
    },
    dataset: datasetCopy,
    find(selector: unknown): unknown {
      const child = queryElement(element, selector);
      return child ? elementHandle(child) : undefined;
    },
    findAll(selector: unknown): unknown[] {
      return queryAllElements(element, selector).map(elementHandle);
    },
  };
}

function buildAx(): unknown {
  return {
    find(selector: unknown): unknown {
      const element = queryElement(document, selector);
      return element ? elementHandle(element) : undefined;
    },
    findAll(selector: unknown): unknown[] {
      return queryAllElements(document, selector).map(elementHandle);
    },
  };
}

function buildState(): unknown {
  return {
    snapshots: {},
    ax: buildAx(),
    document,
    window,
    lastAction: null,
    time: 0,
    logs: [],
    exceptions: [],
  };
}

const runtime = {
  extract<T>(getter: (state: unknown) => T, name?: string): Handle {
    const handle: Handle = { current: undefined, previous: undefined };
    const resolvedName = name && name.length > 0 ? name : `extractor_${extractors.length}`;
    extractors.push({
      getter: getter as (s: unknown) => unknown,
      handle,
      name: resolvedName,
    });
    return handle;
  },
  always: noopFormula,
  now: noopFormula,
  next: noopFormula,
  eventually: noopFormula,
  actions(generator: () => unknown): ActionGeneratorHandle {
    const handle: ActionGeneratorHandle = {
      __sanderlingActionGenerator: true,
      __sanderlingKind: "actions",
      generate: generator,
    };
    if (!actionsRoot) actionsRoot = handle;
    return handle;
  },
  weighted(...entries: [number, ActionGeneratorHandle][]): ActionGeneratorHandle {
    const handle: ActionGeneratorHandle = {
      __sanderlingActionGenerator: true,
      __sanderlingKind: "weighted",
      entries,
    };
    actionsRoot = handle;
    return handle;
  },
  from<T>(items: readonly T[]): { generate: () => T | undefined } {
    return {
      generate(): T | undefined {
        if (items.length === 0) return undefined;
        return items[Math.floor(random() * items.length)];
      },
    };
  },
  tap(p: { on: unknown }): unknown {
    return { kind: "Tap", on: p.on };
  },
  doubleTap(p: { on: unknown }): unknown {
    return { kind: "DoubleTap", on: p.on };
  },
  longPress(): unknown {
    // Why: web has no long-press gesture for v1; the factory returns null so LongPress() calls no-op.
    return null;
  },
  scroll(): unknown {
    // Why: web has no native scroll gesture for v1; the factory returns null so Scroll() calls no-op.
    return null;
  },
  inputText(p: { into: unknown; text: string }): unknown {
    return { kind: "InputText", into: p.into, text: p.text };
  },
  swipe(_p: { from: unknown; to: unknown; durationMillis?: number }): unknown {
    // Why: web has no swipe gesture; the factory returns null so Swipe() calls in specs no-op.
    return null;
  },
  pressKey(p: { key: string }): unknown {
    if (!WEB_PRESS_KEYS.includes(p.key)) {
      throw new Error(
        `pressKey: unsupported key ${JSON.stringify(p.key)} (allowed: ${WEB_PRESS_KEYS.join(", ")})`,
      );
    }
    return { kind: "PressKey", key: p.key };
  },
  wait(p: { durationMillis: number }): unknown {
    return { kind: "Wait", durationMillis: p.durationMillis };
  },
  taps: { __sanderlingActionGenerator: true, __sanderlingKind: "taps" } as ActionGeneratorHandle,
  doubleTaps: { __sanderlingActionGenerator: true, __sanderlingKind: "doubleTaps" } as ActionGeneratorHandle,
  longPresses: { __sanderlingActionGenerator: true, __sanderlingKind: "longPresses" } as ActionGeneratorHandle,
  scrolls: { __sanderlingActionGenerator: true, __sanderlingKind: "scrolls" } as ActionGeneratorHandle,
  typing: { __sanderlingActionGenerator: true, __sanderlingKind: "typing" } as ActionGeneratorHandle,
  swipes: { __sanderlingActionGenerator: true, __sanderlingKind: "swipes" } as ActionGeneratorHandle,
  waitOnce: { __sanderlingActionGenerator: true, __sanderlingKind: "waitOnce" } as ActionGeneratorHandle,
  pressKeys: { __sanderlingActionGenerator: true, __sanderlingKind: "pressKey" } as ActionGeneratorHandle,
};

// Lock the runtime globals so a misbehaving (or malicious) page script can't
// shadow or replace them between AddScriptToEvaluateOnNewDocument running and
// the host invoking the extractor/next-action callbacks.
defineLockedGlobal("__sanderling__", runtime);

function defineLockedGlobal(name: string, value: unknown): void {
  Object.defineProperty(globalThis, name, {
    value,
    writable: false,
    configurable: false,
    enumerable: false,
  });
}

function evaluateExtractors(): Record<number, unknown> {
  const state = buildState();
  const result: Record<number, unknown> = {};
  for (let i = 0; i < extractors.length; i++) {
    const entry = extractors[i];
    if (!entry) continue;
    entry.handle.previous = entry.handle.current;
    let value: unknown;
    try {
      value = entry.getter(state);
    } catch {
      value = undefined;
    }
    entry.handle.current = value;
    result[i] = sanitize(value);
  }
  return result;
}

// SANITIZE_MAX_DEPTH bounds how far sanitize will recurse. State exposes
// `document` and `window`, both of which contain cycles; without a depth or
// seen-set guard a user extractor returning either crashes the runtime via
// stack overflow.
const SANITIZE_MAX_DEPTH = 32;

function sanitize(value: unknown): unknown {
  return sanitizeAt(value, 0, new WeakSet());
}

function sanitizeAt(value: unknown, depth: number, seen: WeakSet<object>): unknown {
  if (value === null || value === undefined) return value;
  if (typeof value === "function") return undefined;
  if (typeof value !== "object") return value;
  if (depth >= SANITIZE_MAX_DEPTH) return null;
  if (seen.has(value as object)) return null;
  seen.add(value as object);
  if (Array.isArray(value)) {
    return value.map((item) => sanitizeAt(item, depth + 1, seen));
  }
  const out: Record<string, unknown> = {};
  for (const key of Object.keys(value as Record<string, unknown>)) {
    const sub = (value as Record<string, unknown>)[key];
    if (typeof sub === "function") continue;
    out[key] = sanitizeAt(sub, depth + 1, seen);
  }
  return out;
}

function pickWeighted(
  handle: ActionGeneratorHandle,
  rand: () => number = random,
): ActionGeneratorHandle | null {
  const entries = handle.entries ?? [];
  if (entries.length === 0) return null;
  let total = 0;
  for (const [weight] of entries) total += Math.max(0, weight);
  if (total <= 0) return null;
  const pick = rand() * total;
  let cumulative = 0;
  for (const [weight, generator] of entries) {
    cumulative += Math.max(0, weight);
    if (pick < cumulative) return generator;
  }
  return entries[entries.length - 1]?.[1] ?? null;
}

function resolveGenerator(handle: ActionGeneratorHandle): unknown {
  switch (handle.__sanderlingKind) {
    case "actions": {
      const generated = handle.generate?.();
      return pickFromArray(generated);
    }
    case "weighted": {
      const inner = pickWeighted(handle);
      if (!inner) return null;
      return resolveGenerator(inner);
    }
    case "taps":
      return randomTap("Tap");
    case "doubleTaps":
      return randomTap("DoubleTap");
    case "typing":
      return randomInput();
    case "swipes":
      return randomSwipe();
    case "longPresses":
    case "scrolls":
      // Why: web has no long-press or native scroll gesture for v1; both no-op.
      return null;
    case "waitOnce":
      return { kind: "Wait", durationMillis: 500 };
    case "pressKey":
      return randomPressKey();
    default:
      return null;
  }
}

// Per-tick cache so the 16-attempt retry loop in __sanderlingNextAction__
// doesn't re-walk the DOM and re-flush layout on every iteration.
let randomTapCandidates: HTMLElement[] | null = null;

function randomTap(kind: "Tap" | "DoubleTap"): unknown {
  if (!randomTapCandidates) {
    randomTapCandidates = Array.from(
      document.querySelectorAll<HTMLElement>(
        'a, button, input, select, textarea, [role="button"], [onclick]',
      ),
    ).filter((element) => {
      if ((element as HTMLButtonElement).disabled) return false;
      const rect = element.getBoundingClientRect();
      return rect.width > 0 && rect.height > 0;
    });
  }
  const candidates = randomTapCandidates;
  if (candidates.length === 0) return null;
  const picked = candidates[Math.floor(random() * candidates.length)];
  if (!picked) return null;
  const rect = picked.getBoundingClientRect();
  return {
    kind,
    on: {
      x: Math.round(rect.left + rect.width / 2),
      y: Math.round(rect.top + rect.height / 2),
    },
  };
}

// Per-tick cache mirroring randomTapCandidates, reset each NextAction tick.
let randomInputCandidates: HTMLElement[] | null = null;

const NON_TEXT_INPUT_TYPES = [
  "button", "submit", "checkbox", "radio", "range", "color", "file", "image", "reset",
];

// Edge-case input pool mirroring the goja-side inputCorpus: empty, whitespace,
// overflow length, unicode, numeric boundaries, and common injection payloads.
const WEB_INPUT_CORPUS = [
  "", "a", "a".repeat(4096), "🙂🔥💸", "  ", "\t\n", "-1",
  "999999999999999999999", "0.0000001", "1e10", "'; DROP TABLE--",
  "<script>alert(1)</script>", "../../etc/passwd", "%s%n", "NaN",
];

function isEditableElement(element: HTMLElement): boolean {
  if (element.isContentEditable) return true;
  const tag = element.tagName.toLowerCase();
  if (tag === "textarea") return true;
  if (tag === "input") {
    const type = ((element as HTMLInputElement).type || "").toLowerCase();
    return !NON_TEXT_INPUT_TYPES.includes(type);
  }
  return false;
}

function randomInput(): unknown {
  if (!randomInputCandidates) {
    randomInputCandidates = Array.from(
      document.querySelectorAll<HTMLElement>("input, textarea, [contenteditable]"),
    ).filter((element) => {
      if (!isEditableElement(element)) return false;
      if ((element as HTMLInputElement).disabled) return false;
      const rect = element.getBoundingClientRect();
      return rect.width > 0 && rect.height > 0;
    });
  }
  const candidates = randomInputCandidates;
  if (candidates.length === 0) return null;
  const picked = candidates[Math.floor(random() * candidates.length)];
  if (!picked) return null;
  const rect = picked.getBoundingClientRect();
  const text = WEB_INPUT_CORPUS[Math.floor(random() * WEB_INPUT_CORPUS.length)];
  return {
    kind: "InputText",
    into: {
      x: Math.round(rect.left + rect.width / 2),
      y: Math.round(rect.top + rect.height / 2),
    },
    text,
  };
}

function randomSwipe(): unknown {
  // Why: web has no swipe gesture; pointer drags into empty divs are noise.
  return null;
}

const WEB_PRESS_KEYS = ["enter", "tab", "escape", "up", "down", "left", "right"];

function randomPressKey(): unknown {
  // Why: only emit keys with meaningful browser semantics; "back"/"home" don't navigate.
  const key = WEB_PRESS_KEYS[Math.floor(random() * WEB_PRESS_KEYS.length)];
  return { kind: "PressKey", key };
}

function pickFromArray(value: unknown): unknown {
  if (!value) return null;
  if (!Array.isArray(value)) return value;
  if (value.length === 0) return null;
  return value[Math.floor(random() * value.length)];
}

function serializeAction(action: unknown): unknown {
  if (!action || typeof action !== "object") return null;
  const obj = action as Record<string, unknown>;
  switch (obj.kind) {
    case "Tap": {
      const point = pointOf(obj.on);
      if (!point) {
        console.warn("[sanderling] Tap target did not resolve to coordinates");
        return null;
      }
      return { kind: "Tap", x: point.x, y: point.y };
    }
    case "DoubleTap": {
      const point = pointOf(obj.on);
      if (!point) {
        console.warn("[sanderling] DoubleTap target did not resolve to coordinates");
        return null;
      }
      return { kind: "DoubleTap", x: point.x, y: point.y };
    }
    case "InputText": {
      const point = pointOf(obj.into);
      if (!point) {
        console.warn("[sanderling] InputText target did not resolve to coordinates");
        return null;
      }
      return {
        kind: "InputText",
        x: point.x,
        y: point.y,
        text: obj.text ?? "",
      };
    }
    case "Swipe": {
      const from = pointOf(obj.from);
      const to = pointOf(obj.to);
      if (!from || !to) {
        console.warn("[sanderling] Swipe endpoints did not resolve to coordinates");
        return null;
      }
      return {
        kind: "Swipe",
        from_x: from.x,
        from_y: from.y,
        to_x: to.x,
        to_y: to.y,
        duration_millis: obj.durationMillis ?? 250,
      };
    }
    case "LongPress":
    case "Scroll":
      // Why: web has no long-press or native scroll gesture for v1; drop the action.
      return null;
    case "PressKey":
      return { kind: "PressKey", key: obj.key };
    case "Wait":
      return { kind: "Wait", duration_millis: obj.durationMillis ?? 0 };
    default:
      return null;
  }
}

function pointOf(value: unknown): { x: number; y: number } | undefined {
  if (!value || typeof value !== "object") return undefined;
  const obj = value as Record<string, unknown>;
  if (typeof obj.x === "number" && typeof obj.y === "number") {
    return { x: obj.x, y: obj.y };
  }
  return undefined;
}

defineLockedGlobal("__sanderlingExtractors__", function (): Record<number, unknown> {
  return evaluateExtractors();
});

defineLockedGlobal("__sanderlingNextAction__", function (): unknown {
  // The spec assigns its root to globalThis.actions (a data tree from
  // @sanderling/spec actions.ts that carries the legacy __sanderlingKind tags
  // this picker reads). Fall back to a root captured via __sanderling__ for the
  // bundler stub specs that still call the old factories.
  const root = (globalThis as { actions?: ActionGeneratorHandle }).actions ?? actionsRoot;
  if (!root) return null;
  // Reset per-tick caches so each invocation gets a fresh DOM scan.
  randomTapCandidates = null;
  randomInputCandidates = null;
  // Match the goja runtime: retry up to 16 times when a weighted entry's
  // generator returns []. Otherwise on routes where most generators are
  // gated to other pages, ~80% of ticks would emit no action.
  for (let attempt = 0; attempt < 16; attempt++) {
    const action = serializeAction(resolveGenerator(root));
    if (action !== null) return action;
  }
  return null;
});

// Test-only exports. The IIFE bundle the host installs has no export surface,
// so these are stripped from production output; they only exist for unit tests.
export const __testing__ = {
  mulberry32,
  deriveSeed32,
  pickWeighted,
  WEB_INPUT_CORPUS,
  WEB_PRESS_KEYS,
};

export {};