tracing library

Recording and replaying agent sessions.

A generative interface has a problem an ordinary app does not: the screen that failed is not in the source. A model composed it, once, from a context that will not come back. When someone reports that "the confirm button did nothing", there is no screen to open and no state to inspect.

A trace is that session, kept: every message the agent sent, the contents of each surface's data model whenever they changed, and every action the app sent back. Because A2UI describes interfaces as data rather than code, replaying a trace is deterministic — the same messages build the same surfaces, with no model and no network.

Record:

final recorder = GenUiTraceRecorder.attach(
  controller,
  catalogId: catalog.catalogId,
  redact: const ['/user/email'],
);

transport.messages.listen(recorder.handleMessage);
...
await File('bug-4821.a2ui-trace').writeAsString(recorder.build().encode());

Replay, in a test or on a debug screen:

final trace = GenUiTrace.decode(await File('bug-4821.a2ui-trace').readAsString());
final player = GenUiTracePlayer(trace, catalog: genUiCatalog)..seek(7);

await tester.pumpWidget(MaterialApp(home: GenUiTraceView(player: player)));
expect(find.text('Confirm'), findsOneWidget);

Replaying against the app's current catalog is the useful default: an old session rendered by today's components is how a catalog change that breaks a real conversation shows up before a user finds it.

Two things worth setting up on the first day rather than the worst day. Name the data model paths that hold personal information in redact, since a recording keeps what the user typed. And keep anything a component reads from outside the data model — a clock, a random number, a request — behind a function the catalog declares, or the replay will diverge from the session in exactly the places that are hardest to notice.

Classes

Constants

genui_gen package

tracing library