Telemetry and provenance

Every reading says where it came from, and there is no way to say “made up”.

The three sources

type TelemetrySource = 'hardware' | 'derived' | 'unavailable';

Source	Means
'hardware'	Read from a device API during this run.
'derived'	Computed from hardware readings, and labelled as computed — useAltimeter’s altitude, worked out from barometric pressure, is derived.
'unavailable'	Could not be read. The value is null, and renders as an em dash.

There is deliberately no 'simulated'. Nothing in the SDK fabricates a reading, and the type makes that unrepresentable rather than leaving it to a reviewer to catch.

Where it appears

• On every hook. Each hook returns source, so a component can always answer “is this number real?” before it shows it.
• On every metric. recordMetric takes a source, and traced tags the duration it records with one — 'hardware' unless the call passes 'derived'.
• Per module. getSourceSummary() reports which sources each module is currently producing, which is how the template’s Dashboard shows provenance module by module.

The rendering rule

A value that could not be read is shown as “—”, never as a plausible number. A blank is honest; a substitute is not, and it is worse than nothing because it looks like a reading.

System telemetry

Kernel scheduling, CPU and GPU clock changes and app markers come from usePerfetto, written to a system trace file by the Android tracing service. That runs below this layer and is not tagged with a TelemetrySource.

Limits

Telemetry never leaves the device: there is no exporter to a backend. That, and what it would take, is on the Observability overview.