Document smoke-test diagnostics

docs/internal/observation.md

@@ -41,6 +41,11 @@ attempts above the first in a generation, and repair generations with at least
 one dispatch. A terminal event is an aggregate and must not be added to its
 attempt events.
 
+Smoke diagnostics mask inherited execution-recorder state while invoking
+generation or HTTP collaborators. Their private attempt evidence is assembled
+into a `SmokeTestReport`; it does not create ordinary run events or enter an
+enclosing run's observation totals.
+
 The [recorder tests](../../internal/observation/recorder_test.go) own usage
 presence, phase sums, event ordering, empty-run accounting, identity snapshots,
 and callback panic behavior. The [generation coordinator](generation.md) owns