fix(settings): stop offering a column the backend rejects

Settings -> Track List Columns listed two rows both called "Track
Name", one of which could not be ticked, and a screen reader heard
"Show the Track Name column" twice with nothing to tell them apart.

They are `titleArtist` and `trackName`, and the issue left open which
way to fix it: a second label so the sort dropdown and the configurator
can say different words, or drop the row because the user cannot select
it. The code settles that. `titleArtist` is not in
`tracklist.AllColumnIDs`, so `Config.Validate()` returns `unknown
track-list column ID: "titleArtist"` -- ticking the row sends a column
set the backend rejects, `config-page` swallows the rejection into a
`console.error`, and the tick reverts. A second label would have named
a control that cannot work.

So a definition says whether it is a *choice*, and the configurator
reads `CONFIGURABLE_COLUMN_IDS` rather than `Object.keys(COLUMN_DEFS)`.

The new test reads Go's own list out of `backend/tracklist/config.go`
rather than writing it down a third time, since a third copy is the
fault one step earlier. Verified by planting: with the filter removed
all four assertions fail with the defect's own numbers.

Not fixed here, and filed as #231: `SetTrackListColumns` assigns before
it validates, so a rejected list stays in memory and `Save()` validates
the whole config -- one tick and no setting saves for the rest of the
session. That is reachable from any invalid input, not from this row.

Closes #197

frontend/src/components/config-page/config-page.ts

@@ -51,7 +51,7 @@ import type { BackgroundShade } from '@store/theme-store';
 import type { IconStyle } from '@store/favorites-store';
 import {
     COLUMN_DEFS,
-    ALL_COLUMN_IDS,
+    CONFIGURABLE_COLUMN_IDS,
 } from '@components/track-list/columns';
 
 import './config-field';
@@ -1640,7 +1640,7 @@ export class ConfigPage extends ViewLifecycleMixin(LitElement) {
             ...this.trackListCtrl.columnIds,
         ];
 
-        const disabledIds = ALL_COLUMN_IDS.filter(
+        const disabledIds = CONFIGURABLE_COLUMN_IDS.filter(
             (id) => !enabledIds.includes(id),
         );
 

frontend/src/components/track-list/columns.ts

@@ -32,6 +32,18 @@ export interface ColumnDef {
     id: string;
     /** Human-readable header label. */
     label: string;
+    /**
+     * Whether Settings may offer this column. Defaults to true.
+     *
+     * A definition is not the same thing as a *choice*. `titleArtist`
+     * is the phone's stacked column, picked by width in
+     * `PHONE_COLUMN_IDS`, and `tracklist.AllColumnIDs` in Go does not
+     * list it — so a tick in the configurator sends a column set the
+     * backend rejects with `unknown track-list column ID`, the tick
+     * reverts on the next render, and the only trace is a
+     * `console.error` (#197).
+     */
+    configurable?: boolean;
     /** Extracts the display value from a track. */
     accessor: (track: library.Track) => string;
     /** Default CSS width (used when no saved width exists). */
@@ -98,11 +110,16 @@ export const COLUMN_DEFS: Record<string, ColumnDef> = {
     },
     titleArtist: {
         id: 'titleArtist',
-        // Named for what it sorts by, since that is the only place the
-        // label is user-visible: the phone has no column headers, and
-        // the page header's sort list is built from the *configured*
-        // columns rather than the drawn ones.
+        // Named for what it sorts by. That label is drawn nowhere
+        // today: the phone has no column headers, and the page header's
+        // sort list is built from the *configured* columns, which this
+        // one can never be — see `configurable` below.
         label: 'Track Name',
+        // Chosen by width, never by the user, and rejected by the
+        // backend if it ever were. #197: Settings listed it anyway, so
+        // there were two rows called "Track Name" and the second one
+        // could not be selected.
+        configurable: false,
         accessor: (t) => t.TrackName,
         defaultWidth: '1fr',
         comparator: (a, b) => compareStr(a.TrackName, b.TrackName),
@@ -266,10 +283,15 @@ export const COLUMN_DEFS: Record<string, ColumnDef> = {
 };
 
 /**
- * All column IDs in default display order.
- * Used by the settings UI to list available columns.
+ * The column IDs Settings may offer, in default display order.
+ *
+ * Not every definition is one: a column the user cannot choose has no
+ * row in the configurator, because a checkbox that cannot change
+ * anything is worse than an absent one — see `ColumnDef.configurable`.
  */
-export const ALL_COLUMN_IDS: string[] = Object.keys(COLUMN_DEFS);
+export const CONFIGURABLE_COLUMN_IDS: string[] = Object.keys(
+    COLUMN_DEFS,
+).filter((id) => COLUMN_DEFS[id]?.configurable !== false);
 
 /**
  * Column IDs that are always searched regardless of visibility.