fix(trace): an action names the generator that produced it

The setup exclusion landed for the model arm only, because only a model
pick stamped a source. A seeded run returned setup's action through the
same entry with no marker, so its denominator still counted the login
while the model arm's did not, and the two are compared.

serializeAction names setup and seeded on the wire, so both arms are
counted by one rule. An already-recorded trace names nothing and keeps
exactly the count it was reported with; unattributed_actions counts those
steps so the old denominator cannot pass as the new one. TraceVersion is
deliberately unbumped: oracle-reduction refuses a differing version, and
a bump would make all 169 recorded runs unreplayable.

internal/verifier/types.go

@@ -38,6 +38,10 @@ type Action struct {
 	// when the apply call failed and nothing can say whether the action
 	// reached the app. The spec is told which of the two it is.
 	Applied bool
+	// Source names the generator that produced this action, "setup" or
+	// "seeded", as the runtime entry tagged it. Empty on an action the runner
+	// built itself (the model policy's pick), which the runner names instead.
+	Source string
 	// Relaunched, like Applied, is meaningful only on state.lastAction: the
 	// runner brought the app back to the foreground after this action, so the
 	// two readings the spec compares straddle a restart. The action still