feat(ui): the track list a phone can read

B2 phase 4, and the last of it. Measured on the device: at 424 CSS px
the four configured columns fit the row *exactly* -- `--grid-cols` came
out `24px 102px 101px 101px 80px` -- and not one of them fit its
content, with "Duration" too narrow for its own header. The columns were
never too wide; there were too many of them.

So a phone draws `titleArtist` (the title with the artist under it,
across the row's whole width) plus the duration, and drops the column
headers and the resize handles, which are a click-to-sort and a drag
with no touch equivalent. It is a **column set, not a second row
template**: the row, its delegated events, the selection semantics, the
playing marker and the virtualizer never learn anything changed, because
from their side only the number of columns did.

Three rules come with it. The row height is in two places
(`PHONE_ROW_HEIGHT` and the CSS rule) and must agree, since the
virtualizer positions rows from that number and a taller row overlaps
its neighbour. What is drawn and what can be sorted are different
questions, so the sort list is built from `configuredColumns` -- a phone
has no headers either, and building it from the drawn columns would
leave it able to sort by title and duration alone. And a phone's column
widths are neither loaded nor saved.

That third rule is the bug the device found with the arrangement already
passing five component tests and five e2e specs at the phone's own
viewport. `loadColumnWidths` is keyed by column *id* and fills a gap
with `MIN_COLUMN_WIDTH`, so the stacked column -- which nothing can ever
have saved a width for -- came out at 148px beside a duration column of
236. The mirror image was worse and unreachable from a phone at all:
saving would have written those widths back under the same ids,
replacing the width the user dragged on a desktop. The specs asserted
shape, and the fault depended on what `localStorage` held for a
different column set; the unit test now carries that map as a fixture.

Verified: 809 component tests, 112 e2e specs, and on the phone at
424x439 -- `24px 304px 80px`, 52px rows, no truncation, no overflow.
One full e2e run of three saw an unrelated autotag keypress spec flake
and pass on retry.

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

@@ -9,6 +9,8 @@ import {
 import { formatMilliseconds } from '@utils/time';
 import { html, nothing } from 'lit';
 
+import { highlightText } from './search-ranking';
+
 /** Compares two strings using locale-aware ordering. */
 const compareStr = (
     a: string,
@@ -36,8 +38,17 @@ export interface ColumnDef {
     defaultWidth: string;
     /** Text alignment. Defaults to left. */
     align?: 'left' | 'right';
-    /** Optional custom render function returning an HTML template. */
-    renderCell?: (track: library.Track) => unknown;
+    /**
+     * Optional custom render function returning an HTML template.
+     *
+     * `term` is the active search term, for a cell that wants to
+     * highlight its own text: the default path applies `highlightText`
+     * to `accessor`'s value, and a cell that renders itself has to do
+     * that itself or silently lose the highlight. Only `titleArtist`
+     * needs it, which is why it is optional rather than a second
+     * required parameter on all of them.
+     */
+    renderCell?: (track: library.Track, term?: string) => unknown;
     /**
      * Comparison function for sorting two tracks by this column.
      * Returns negative if a < b, positive if a > b, zero if equal.
@@ -85,6 +96,27 @@ 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.
+        label: 'Track Name',
+        accessor: (t) => t.TrackName,
+        defaultWidth: '1fr',
+        comparator: (a, b) => compareStr(a.TrackName, b.TrackName),
+        renderCell: (t, term) => html`
+            <div class="stacked">
+                <span class="stacked-title"
+                    >${term ? highlightText(t.TrackName, term) : t.TrackName}</span
+                >
+                <span class="stacked-sub"
+                    >${term ? highlightText(t.ArtistName, term) : t.ArtistName}</span
+                >
+            </div>
+        `,
+    },
     trackName: {
         id: 'trackName',
         label: 'Track Name',
@@ -249,6 +281,24 @@ export const CORE_SEARCH_COLUMN_IDS: string[] = [
     'album',
 ];
 
+/**
+ * The one column a phone shows, and it is two lines.
+ *
+ * At 424 CSS px -- the width of the phone this was measured on -- four
+ * columns fit the row exactly and none of them fits its *content*:
+ * `--grid-cols` came out `24px 102px 101px 101px 80px`, so "Duration"
+ * did not fit its own header and a title had ~20 characters. The
+ * columns were never too wide; there were too many of them.
+ *
+ * So the phone gets the title with the artist under it, which is the
+ * shape every phone music list has, and the full row width to put them
+ * in. It is a *column definition* rather than a second row template on
+ * purpose: the row, the delegated events, the selection semantics, the
+ * playing marker and the virtualizer all keep working, because from
+ * their side nothing has changed except how many columns there are.
+ */
+export const PHONE_COLUMN_IDS: string[] = ['titleArtist', 'trackLength'];
+
 /**
  * Default column IDs. Album is in them (H-15): without it, the three
  * `Tideline / Aurora Fields / 00:06` rows in this app's own fixture

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

@@ -30,6 +30,7 @@ import { LibraryController } from '@store/controllers/library-controller';
 import {
     COLUMN_DEFS,
     DEFAULT_COLUMN_IDS,
+    PHONE_COLUMN_IDS,
 } from './columns';
 import type { ColumnDef } from './columns';
 import { classMap } from 'lit/directives/class-map.js';
@@ -90,6 +91,18 @@ const ROW_PADDING_X = 8;
 const ROW_CHROME_WIDTH =
     FAV_COL_WIDTH + ROW_PADDING_X * 2;
 
+/**
+ * Row heights, in the same relationship as the widths above: the number
+ * is read by the CSS *and* by the virtualizer's layout, so they cannot
+ * disagree. A phone row is two lines (title over artist).
+ */
+const ROW_HEIGHT = 33;
+const PHONE_ROW_HEIGHT = 52;
+
+/** The shell's phone breakpoint, as `index.css` and every component
+ *  stylesheet spells it. */
+const PHONE_QUERY = '(max-width: 599px)';
+
 // Inline SVG paths for favorite icons — eliminates wa-icon shadow DOM
 // overhead (30-50 shadow roots during scroll).  Font Awesome 6 paths.
 const FAV_ICONS = {
@@ -175,19 +188,34 @@ export class TrackList
      * Resolved column definitions for the currently configured
      * column IDs.  Falls back to defaults for any unknown ID.
      */
-    private get activeColumns(): ColumnDef[] {
+    /**
+     * The columns the user has chosen — what a desktop draws, and what
+     * *anything* may be sorted by.
+     *
+     * This is deliberately separate from `activeColumns`: "which columns
+     * are drawn" and "what can I sort by" are different questions, and
+     * the phone is exactly where they diverge. Building the sort list
+     * from the drawn columns would silently take sort-by-artist and
+     * sort-by-album away from the phone, which has no other route to
+     * them since it has no column headers either.
+     */
+    private get configuredColumns(): ColumnDef[] {
         const ids = this.trackListCtrl.columnIds;
+        const chosen = !ids || ids.length === 0 ? DEFAULT_COLUMN_IDS : ids;
 
-        if (!ids || ids.length === 0) {
-            return DEFAULT_COLUMN_IDS
-                .map((id) => COLUMN_DEFS[id])
-                .filter(
-                    (d): d is ColumnDef =>
-                        d !== undefined,
-                );
-        }
+        return chosen
+            .map((id) => COLUMN_DEFS[id])
+            .filter(
+                (d): d is ColumnDef =>
+                    d !== undefined,
+            );
+    }
 
-        return ids
+    /** The columns actually drawn: two stacked lines on a phone. */
+    private get activeColumns(): ColumnDef[] {
+        if (!this.phone) return this.configuredColumns;
+
+        return PHONE_COLUMN_IDS
             .map((id) => COLUMN_DEFS[id])
             .filter(
                 (d): d is ColumnDef =>
@@ -374,9 +402,42 @@ export class TrackList
     // doesn't need to measure items. Without this hint, the default 100px
     // estimate causes constant scroll error correction (scrollTo() calls)
     // that produce visible jumping/skipping during scroll.
+    /**
+     * The virtualizer's item size and the CSS row height are the same
+     * number in two places, and they must agree: the layout positions
+     * rows from this figure, so a row that is really taller overlaps its
+     * neighbour and a shorter one leaves a gap. Both come from here.
+     */
     private flowLayout = flow({
-        _itemSize: { width: 100, height: 33 },
+        _itemSize: { width: 100, height: ROW_HEIGHT },
     } as Parameters<typeof flow>[0]);
+
+    private phoneFlowLayout = flow({
+        _itemSize: { width: 100, height: PHONE_ROW_HEIGHT },
+    } as Parameters<typeof flow>[0]);
+
+    private get rowLayout(): Parameters<typeof flow>[0] {
+        return this.phone ? this.phoneFlowLayout : this.flowLayout;
+    }
+
+    /**
+     * Phone width, from the shell's own breakpoint.
+     *
+     * A media query *inside* a shadow root is answered by the viewport,
+     * which is what lets every other component state what it drops at
+     * phone width in its own stylesheet. This list cannot: its grid is
+     * computed in JS from the host width, so the same threshold has to
+     * be readable from JS as well. One breakpoint, two expressions of
+     * it, and the reason is written here rather than inferred.
+     */
+    @state()
+    private phone = matchMedia(PHONE_QUERY).matches;
+
+    private phoneQuery = matchMedia(PHONE_QUERY);
+
+    private onPhoneChange = (e: MediaQueryListEvent): void => {
+        this.phone = e.matches;
+    };
     private hasRestoredScroll = false;
     private scrollSaveRAFId: number | null = null;
 
@@ -543,6 +604,20 @@ export class TrackList
     }
 
     private initColumnWidths() {
+        // A phone's widths are never the saved ones. `loadColumnWidths`
+        // is keyed by column *id* and fills a gap with
+        // `MIN_COLUMN_WIDTH`, so the phone's stacked column -- which
+        // nothing has ever saved a width for, there being no handles to
+        // drag -- came out at the minimum while the duration column
+        // inherited a width saved for a four-column desktop row. Found
+        // on the device: `24px 148px 236px`, the duration column with
+        // 55% of a phone's row.
+        if (this.phone) {
+            this.computeDefaultWidths();
+
+            return;
+        }
+
         const saved = this.loadColumnWidths();
         const cols = this.activeColumns;
 
@@ -673,6 +748,13 @@ export class TrackList
     }
 
     private saveColumnWidths() {
+        // And a phone's widths are never *saved*: they are computed from
+        // a column set the user did not choose, and writing them would
+        // overwrite the width they dragged for the same column on a
+        // desktop. Nothing on a phone can resize a column anyway, so
+        // this is only reachable by a window crossing the breakpoint.
+        if (this.phone) return;
+
         try {
             const cols = this.activeColumns;
 
@@ -1045,6 +1127,35 @@ export class TrackList
       contain: strict;
     }
 
+    /* A phone row is two lines, and this height must equal
+       PHONE_ROW_HEIGHT: the virtualizer positions rows from that number,
+       so a taller row overlaps its neighbour and a shorter one gaps. */
+    @media (max-width: 599px) {
+      .track-row {
+        height: 52px;
+      }
+    }
+
+    .stacked {
+      display: flex;
+      flex-direction: column;
+      justify-content: center;
+      gap: 2px;
+      min-width: 0;
+    }
+
+    .stacked-title,
+    .stacked-sub {
+      overflow: hidden;
+      text-overflow: ellipsis;
+      white-space: nowrap;
+    }
+
+    .stacked-sub {
+      font-size: var(--yj-text-xs);
+      color: var(--yj-text-secondary, #b3b3b3);
+    }
+
     .track-row > * {
       min-width: 0;
     }
@@ -1171,9 +1282,17 @@ export class TrackList
         );
 
         this.resizeObserver.observe(this);
+
+        // Connection, not the view lifecycle: this only sets state, so
+        // it is harmless (and wanted) while the list is off screen -- a
+        // rotation on another view must not leave this one laid out for
+        // the wrong width when the user comes back to it.
+        this.phoneQuery.addEventListener('change', this.onPhoneChange);
     }
 
     override disconnectedCallback() {
+        this.phoneQuery.removeEventListener('change', this.onPhoneChange);
+
         // Remove delegated event handlers from virtualizer.
         const virt = this.virtualizer;
         if (virt) {
@@ -2017,7 +2136,7 @@ export class TrackList
           </svg>
         </div>
         ${cols.map((col) => {
-                const customCell = col.renderCell?.(track);
+                const customCell = col.renderCell?.(track, term);
                 if (customCell !== undefined && customCell !== nothing) {
                     return html`<div role="gridcell" class="cell">${customCell}</div>`;
                 }
@@ -2065,7 +2184,7 @@ export class TrackList
     private renderPageHeader() {
         const options: SortOption[] = [
             { id: '', label: 'Default' },
-            ...this.activeColumns
+            ...this.configuredColumns
                 .filter((c) => c.comparator)
                 .map((c) => ({ id: c.id, label: c.label })),
         ];
@@ -2115,7 +2234,7 @@ export class TrackList
               aria-busy=${this.loadingTracks}
               @keydown=${this.onListKeydown}
             >
-            <div class="header-row" role="row">
+            ${this.phone ? nothing : html`<div class="header-row" role="row">
               <div role="columnheader" aria-label="Favourite"></div>
               ${cols.map(
                     (col) => html`
@@ -2149,7 +2268,7 @@ export class TrackList
                 </div>
               `,
                 )}
-            </div>
+            </div>`}
             ${visibleTracks.length === 0
                         ? html`<p class="no-results">
                       No tracks match your search.
@@ -2160,12 +2279,14 @@ export class TrackList
                         .items=${visibleTracks}
                         .renderItem=${this.renderTrackRow}
                         .keyFunction=${(track: library.Track) => track.FilePath}
-                        .layout=${this.flowLayout}
+                        .layout=${this.rowLayout}
                       ></lit-virtualizer>
                     `}
 
+      <!-- Resizing is a pointer gesture with no touch equivalent, and
+           the phone's two columns are not the user's to arrange. -->
       <div class="resize-overlay">
-        ${this.colBoundaryPositions.map(
+        ${(this.phone ? [] : this.colBoundaryPositions).map(
                         (pos, i) => html`
             <div
               class="col-resize-handle ${this.resizingColumn === i ? 'active' : ''}"