Unit toast-postblock - research & requirements

Superseded by notifications-rework-plan.md (2026-11-14 HITL rework). Do not implement against the Must/Must-not below when they conflict with that plan.

User job

After a hard block, decide Keep / Allow (forever or timed) or Decide later - via compact decision dialog (not GNOME notify-send action banners).

Legacy notes (obsolete)

~~Body Host:/Why: labels; quiet re-block -> Activity; follow-up "Always allow: host".~~

Requirements (historical - see plan §0 / §3)

Was Must: human body; Keep / Allow; follow-ups; quiet toast -> History.

Was Must not: change 15s timeout or HITL policy - void: plan changes timeout semantics (no Keep on timeout), primary surface = dialog, timed rules, throttle interval.