Observability Substrate
XMLUI captures every state change, navigation, API call, and sandbox event into a single, structured trace. The same pipeline drives the Inspector overlay you use during development and the audit trail you can ship to a backend in production — there is no second instrumentation layer to set up.
What problems this prevents
- Diagnosing a reactive cascade no longer requires sprinkling
console.logstatements through your markup; the trace already shows which variable, loader, or handler fired and in what order. - A failing API call, a navigation, or a sandbox warning is recorded with enough structure (kind, source location, timing) to reproduce the problem without re-running the user's session.
- Production incidents can be replayed from the trace stream instead of reconstructed from screenshots and stack traces.
- Security-relevant events — banned DOM access, fetch attempts to disallowed origins, clipboard writes, navigations — are visible in one place rather than scattered across the browser console.
How it works
The framework writes structured entries into a circular in-memory buffer
through a single internal pushXsLog() call. Every interesting event has
a well-known kind value (for example app:fetch, navigate,
clipboard:copy, ws:connect, sandbox:warn, log:info,
reactive-cycle). The Inspector overlay renders the buffer live during
development. The audit pipeline can sample and forward the same entries
to an OTLP/JSON sink in production.
Trace entries are emitted by the framework itself — you do not annotate your components to participate. New trace kinds are added as new managed features ship, so the audit surface grows automatically with the framework.
Using the Inspector
Open the Inspector overlay in development to watch the trace stream as
your app runs. Each entry shows its kind, timestamp, source location (if
known), and structured payload. Filtering by kind is the fastest way to
focus on a specific subsystem — for example showing only app:fetch
entries while debugging a network problem.