The fixture mirrors the host's plan unit: a double-event fold over
command/run (name plan) and plan/mode serves the {active, pending} value in
the projections baseline and advances it with session/projection frames;
/plan joins the command catalog with the host handler's wording; the prompt
path commits an outstanding selection as plan/mode inside the opened turn
(the agent/step boundary parallel). Baseline expectations in the fixture
specs gain the always-present plan key.