[SimonHeybrock]

Monitor and detector-view params selected the spectral axis with a coordinate_mode group next to four groups, toa_edges, toa_range, wavelength_edges and wavelength_range, each range with an enabled flag. A request carried the fields of both axes, and the UI showed all of them as separate tabs, whichever axis was selected.

This applies ADR 0008 of essapps ("a choice between ways is a union of groups; X | None means without X"): the five fields become one, spectral_axis, a union discriminated by kind:

class TOASpectralAxis(BaseModel):
    kind: Literal['toa'] = Field('toa', title="Time of arrival (TOA)", description=...)
    edges: TOAEdges = ...
    range_filter: TOARange | None = None

class WavelengthSpectralAxis(BaseModel): ...  # same shape

SpectralAxis = Annotated[TOASpectralAxis | WavelengthSpectralAxis, Field(discriminator='kind')]

The selector controlled two groups per axis, so each alternative holds both, and the enabled flags become range_filter: X | None. TOA-only specs subclass the params model and narrow the field to TOASpectralAxis, which replaces the validator that rejected wavelength. Factories read axis.kind, axis.edges and axis.range_filter instead of the get_active_* methods.

Dashboard param UI

The generic param widgets gain the two components the ADR asks of a UI generator, plus nesting:

• A union of groups is a card with one radio button per alternative in its header, labelled by the title of the tag field; the card holds the chosen alternative's description and fields. Fields of the other alternatives keep their values while hidden.
• A group typed X | None is a card with a switch in its header, collapsed while off.
• A group nested in a group is a card titled by its field, with its description as a tooltip.
• A Literal of one value, such as a tag, has no widget.
• A union is refused as a field of a group (the ADR makes it a parameter of its own), as are hidden-field paths into a union.

The error highlight of a field is now an outline, since clearing it with border: none removed a card's own border. Literal labels via json_schema_extra, whose only user was the coordinate-mode selector, are removed.

Behaviour changes

• Stored configs in the old shape lose their spectral settings and start from the default axis (TOA, default bins); other groups such as pixel weighting are kept. No migration code. The backend validates params the same way, so the dashboard and backend should be deployed together: an old dashboard talking to a new backend would start jobs with default binning.
• The config dialog falls back to defaults for stored params that do not validate against the current model, e.g. a wavelength axis stored for a spec that is now TOA-only, which previously broke the dialog.
• The range filter defaults to one pulse period in ms instead of 0–10 µs, which matters now that it is one switch away.
• OutputView.params names top-level fields only, so every axis-dependent output now lists spectral_axis in "Affects outputs", without distinguishing edges from range filter.

Test plan

• Open the config of a monitor and a detector view on an instrument with both axes (e.g. LOKI) and on a TOA-only one; switch axes, toggle the range filter, start, and check the job uses the chosen settings.
• Reopen the config of a running job and check the stored axis, edges and range filter are shown.

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