Test-drive fixes: detector families and the context budget
B01: the configuration file may disable a harness-notice detector family (the
settings page only refuses); harness notices become persisted, replayed
developer messages through one helper. B25: the context budget comes from
configuration and the model window only caps it (the default is set by
U9). The B02 choice that trimmed payloads
are not retrievable is overridden by U3.