# components/sud.py step lifecycle spec

Confirmed spec for a `Sud` schedule step's internal phase order
(`components/sud.py`), from a design discussion clarifying how `ramp`/
`hold`/user-confirm interact, since implemented (gap-based ramping).

## Phase order

`ramp` -> `hold` -> user-confirm. Every step ramps toward `temperature`
first - this is *not* gated by whether the step has its own `ramp` block
(`_build_step()` always synthesizes one from `default.step.ramp`,
`sud.py:35-52`); `_advance()` (`sud.py:192-204`) always enters `RAMPING`.
How long that actually takes depends on the real gap, decided by the
temperature controller's own gap-tracking FSM
(`TempControllerBase.is_holding()`, `components/pid/temp_controller_base.py`)
rather than any fixed tolerance - `SudTask.on_process()`
(`tasks/sud.py:200-203`) calls `sud.temp_reached()` once `tc.is_holding()`
is true. `set_theta_soll()` recomputes the FSM eagerly
(`temp_controller_base.py:81-89`) so `is_holding()` can't read one tick
stale after a new target is pushed.

`temperature` is the one field deliberately *not* defaulted from
`default.step` (`sud.py:52`) - every `sude/*.json`'s
`default.step.temperature` is inert template filler, never a real shared
target. A step omitting it has no new target of its own: `SudTask`/
`SudForecastEstimator`/the demo driver all skip pushing `set_theta_soll`
in that case (`step['temperature'] is not None` guard), so the controller
just keeps whatever the previous step left running and the ramp resolves
immediately. `hold` stays opt-in, gated by raw presence as before.

## Duration `0`

Supported for hold: `hold_remaining = duration * 60.0` can be `0`;
`tick()` (`sud.py:186-190`) finishes the step on the next tick once
`hold_remaining <= 0`.

## End-of-step branching

`_finish_step()` (`sud.py:212-216`): no `user_wait_for_continue` ->
advances immediately to the next step; `user_wait_for_continue: true`
-> enters `WAIT_USER`, resumed only by `confirm()`.

`WAIT_USER` is not "hold, prolonged": `HOLDING` and `WAIT_USER` are
distinct `SudState` values. The hold countdown runs to completion
*before* `WAIT_USER` begins - `tick()` only decrements
`hold_remaining` while `state == HOLDING`, so the timer is frozen
(not extended) during the wait. It delays the next step, but it's a
separate third phase, not a longer hold.

The gating field is `user_wait_for_continue`, not "presence of a user
message": `user_message` (display text) and `user_wait_for_continue`
(the actual block) are independent fields - a step can show a message
without blocking, or block silently.

## Resolved

- [x] **Pure-hold steps never (re-)set the controller's target
  temperature.** Moot now that ramping isn't gated by the `ramp` key:
  `SudTask.on_step_changed` pushes `set_theta_soll`/`set_heatrate_soll`
  for *any* step that specifies its own `temperature`, not just ones
  with an explicit `ramp` block.
