feat(spec): add keyedBy(element, tags) identity helper

Joins element.find({testTag: tag})?.text per tag with U+001F as the
delimiter so user-visible text can never collide with the separator.
Returns empty string for an undefined element.

pkg/spec/src/extract.ts

@@ -1,5 +1,17 @@
-import type { Extracted, State } from "./types.ts";
+import type { AccessibilityElement, Extracted, State } from "./types.ts";
 
 export function extract<T>(getter: (state: State) => T): Extracted<T> {
   return globalThis.__sanderling__.extract(getter);
 }
+
+const KEY_DELIMITER = "\x1f";
+
+export function keyedBy(
+  element: AccessibilityElement | undefined,
+  tags: readonly string[],
+): string {
+  if (!element) return "";
+  return tags
+    .map(tag => element.find({ testTag: tag })?.text ?? "")
+    .join(KEY_DELIMITER);
+}

pkg/spec/src/index.ts

@@ -23,7 +23,7 @@ export type {
   WeightedEntry,
 } from "./types.ts";
 
-export { extract } from "./extract.ts";
+export { extract, keyedBy } from "./extract.ts";
 export { always, eventually, next, now } from "./ltl.ts";
 export {
   InputText,