- params.rs: one decode per method; handlers take typed structs
  instead of hand-parsing Value (unknown fields ignored, mistyped
  now BAD_PARAMS, documented in docs/08). Shared severity/until
  parsing, SplitPath/Ratio newtypes, headless unit tests.
- store.rs: set_lifecycle/raise_attention/clear_attention move from
  free functions to Store methods, so one event costs one lock and
  state can never part from its emit; attach/mark_seen/resume route
  through them instead of hand-rolled copies.