DashboardListPane: add getSelectedIdx() / getSelectedDashboard() selection-query getters

[HanSur94]

Problem / motivation

The two Companion list panes are siblings, but only one is programmatically queryable for its current selection — a verified API asymmetry.

• TagCatalogPane exposes its selection and a deselect mutator, and these are actually consumed by the rest of the Companion:
  • getSelectedKeys() (libs/FastSenseCompanion/TagCatalogPane.m:213)
  • getSelectedTags() (:220)
  • deselectKey(key) (:229)
  • Consumers: FastSenseCompanion.m:1954/1989/2295, CompanionEventViewer.m:1158.
  • Its own docstring explains why a getter exists: "the event itself carries no payload" (:215).
• DashboardListPane has no selection query at all. Its public surface is just attach / detach / setTheme / refresh. The current selection lives in the private SelectedIdx_ (libs/FastSenseCompanion/DashboardListPane.m:40), and the pane only fires the payload-free DashboardSelected event (:21).

So there is no way to read which dashboard is currently selected without listening for the event and shadowing the index out-of-band — exactly the bookkeeping TagCatalogPane.getSelectedKeys() was added to eliminate. Verified clean: grep -rnE "getSelectedIdx|getSelectedDashboard" libs/FastSenseCompanion/ returns nothing.

Proposed feature

Give DashboardListPane the dashboard analog of the catalog pane's selection getters:

• idx = getSelectedIdx(obj) → 1-based selected row index, or 0 when none selected.
• eng = getSelectedDashboard(obj) → the selected DashboardEngine handle, or [] when none / stale.

Optional natural sibling (same theme): deselectDashboard(obj) — the analog of TagCatalogPane.deselectKey, clearing SelectedIdx_ and refreshing the row highlight.

Rough sketch

In libs/FastSenseCompanion/DashboardListPane.m, methods (Access = public):

function idx = getSelectedIdx(obj)
%GETSELECTEDIDX Return the 1-based selected row index (0 = none).
    idx = obj.SelectedIdx_;
end

function eng = getSelectedDashboard(obj)
%GETSELECTEDDASHBOARD Return the selected DashboardEngine handle ([] if none).
    eng = [];
    idx = obj.SelectedIdx_;
    if idx >= 1 && idx <= numel(obj.Engines_)
        eng = obj.Engines_{idx};
    end
end

The engine handles are already snapshotted in the private Engines_ cell (DashboardListPane.m:39), so getSelectedDashboard mirrors how getSelectedTags resolves keys against AllTags_. getSelectedIdx mirrors getSelectedKeys returning SelectedKeys_.

Value

Companion API parity for the dashboard list. The event-only model forces any consumer (the inspector, a test, future tooling that acts on "the selected dashboard") to mirror selection state itself. A read-back getter lets a caller ask the pane directly — and getSelectedDashboard returns the live engine handle ready to act on.

Constraints check

• Toolbox-free: ✅ field read + bounds check + cell index; base primitives only.
• Backward-compatible: ✅ brand-new methods; attach/detach/refresh/setTheme, the events block, and SelectedIdx_ semantics are untouched. Panes aren't serialized, so no round-trip impact. Existing Companion scripts behave identically.
• Pure MATLAB/Octave: ✅ no DashboardWidget/Tag contract involved (Companion-internal API).

Effort estimate

S — two tiny getters (plus an optional deselectDashboard mutator) in one file + a test: select row 2 → getSelectedIdx()==2 and getSelectedDashboard() is the right engine handle; no selection → 0/[]; stale index after a shorter refresh → [].

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AI-proposed via /feature-scout — needs a human product decision before implementation.