feat(explore): offer the autotag match on the album page

The complaint was having to notice the metadata was missing, then go
and hunt the album down on the Autotag page. The album page now says it
while you are looking at the thing: "MusicBrainz has a match for this
album: <release> by <artist>", with Apply tags and Review in Autotag.

Four things about it are load-bearing.

**Applying is offered only where it would do the whole album.** A
tagging group is a folder, so a multi-disc album is several, and one
button that applied to the best-scoring group would leave the album
holding a mix of old and new tags — the exact case the app's Blocking
notification level exists for. `groupCount` is the test, and the answer
there is review rather than apply.

**It rewrites files, so it asks.** `confirmAction()` with an impact
line that says it cannot be undone and that nothing is moved or
deleted, because "rewrites your files" reads worse than it is. The
apply goes through `ApplyAsync`, the registered-job path, so progress
belongs to the jobs indicator and this page does not grow a second one
— what it owes the user is the acknowledgement, because the button is
here. The suggestion clears itself on success rather than inviting a
second click while the job runs.

**The banner does not quote a percentage.** The backend has a score and
deliberately keeps it out of the sentence: 0.95 reads as a probability
and is not one. Which release it is, is the part a person can judge.

**"Review in Autotag" lands on that album.** The queue is sorted by
score so the intended folder is often near the top, and "often" is a
link that sometimes opens a different album. Autotag is a cached
primary view, so there is no construction to hand a payload to: the
request goes on as an attribute and the view *consumes* it, or every
later visit would reopen a folder the user finished with long ago.

`ICON_AUTOTAG` joins the vocabulary at the same time, on the rule
`ICON_PLAYLIST` was chosen by — an icon names the noun it acts on, so a
suggestion pointing at Autotag wears the Autotag destination's own
mark. It was written inline in the sidebar; two call sites is where a
name stops being one component's detail, so the sweep governs it now.

Verified against the running app with a staged match: the banner, the
confirm dialog's wording, and the navigation landing on the right
folder with the attribute consumed.

Closes #28

frontend/src/components/autotag-view/autotag-view.ts

@@ -1315,13 +1315,40 @@ export class AutotagView extends ViewLifecycleMixin(LitElement) {
         // the page only needs the folder list, which is local and may
         // have moved while the page was away.
         if (this.queueStarted) {
-            void this.loadFolders();
+            void this.loadFolders().then(() => this.openRequestedFolder());
         } else {
             this.queueStarted = true;
-            void this.startQueue();
+            void this.startQueue().then(() => this.openRequestedFolder());
         }
     }
 
+    /**
+     * Open the folder somebody navigated here to look at.
+     *
+     * The album page's "Review in Autotag" has to land on *that*
+     * album. The queue is sorted by score so the intended folder is
+     * often near the top, but "often" is a link that sometimes opens
+     * the wrong album, which is worse than no link.
+     *
+     * It is an attribute rather than a property because this is a
+     * **cached primary view**: `index.ts` creates it once and reuses
+     * it, so there is no construction to pass a value to. Which is
+     * also why the request is *consumed* — the attribute is removed
+     * once acted on, or every later visit to Autotag would reopen an
+     * album the user finished with three navigations ago.
+     */
+    private openRequestedFolder(): void {
+        const requested = this.getAttribute('group-key');
+
+        if (!requested) return;
+
+        this.removeAttribute('group-key');
+
+        if (this.current?.groupKey === requested) return;
+
+        void this.selectFolder(requested);
+    }
+
     protected override onViewDeactivate(): void {
         this.unsubscribeLibraryStore?.();
         this.unsubscribeLibraryStore = undefined;

frontend/src/components/explore-album-details/explore-album-details.ts

@@ -30,12 +30,16 @@ import { Events } from '../../events';
 import '@awesome.me/webawesome/dist/components/icon/icon.js';
 import '../library-status-indicator/library-status-indicator.js';
 import { libraryStatusFor } from '@utils/library-status';
+import { ICON_AUTOTAG } from '@utils/icon-language';
 import type { LibraryStatus } from '../library-status-indicator/library-status-indicator.js';
 import '../catalog-scope-notice/catalog-scope-notice.js';
 import type { CatalogScope } from '../catalog-scope-notice/catalog-scope-notice.js';
 import '@awesome.me/webawesome/dist/components/button/button.js';
 import '../download-picker/download-picker';
 import { downloadStore } from '../../store/download-store';
+import { MatchForAlbum, ApplyAsync } from '@go/autotagservice/service.js';
+import type * as autotagservice from '@go/autotagservice/models.js';
+import { confirmAction } from '../confirm-dialog/confirm-dialog';
 import { queueStore } from '../../store/queue-store';
 import type { QueueSource } from '../../store/queue-store';
 import { notificationStore } from '../../store/notification-store';
@@ -175,6 +179,19 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
     @property({ type: Number, attribute: 'local-album-id' })
     localAlbumId = 0;
 
+    /**
+     * A confident autotag match for this album, or null when there is
+     * none worth mentioning.
+     *
+     * The tier behind "confident" is `autotag.ConfidentTier`, decided
+     * in the backend so this page and strict auto-accept cannot
+     * disagree about what it means (#28, #90).
+     */
+    @state() private autotagMatch: autotagservice.AlbumMatchView | null = null;
+
+    /** True while an apply started from this page is in flight. */
+    @state() private applyingTags = false;
+
     /* ── Internal state ── */
 
     @state() private releaseGroup: MBReleaseGroup | null = null;
@@ -545,6 +562,57 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
                 flex-shrink: 0;
             }
 
+            /* ── The autotag suggestion ── */
+            .autotag-match {
+                display: flex;
+                align-items: center;
+                flex-wrap: wrap;
+                gap: 8px 12px;
+                margin-bottom: 12px;
+                padding: 10px 14px;
+                border: 1px solid
+                    var(--yj-border-subtle, rgba(255, 255, 255, 0.08));
+                border-radius: 8px;
+                background: var(--yj-surface-1, rgba(255, 255, 255, 0.04));
+            }
+
+            .autotag-match > wa-icon {
+                flex-shrink: 0;
+                font-size: var(--yj-icon-sm);
+                color: var(--yj-text-secondary, #b3b3b3);
+            }
+
+            .autotag-match-text {
+                margin: 0;
+                flex: 1;
+                /* The suggestion sits in a flex row beside its buttons,
+                 * and a grid/flex item's implicit minimum is its
+                 * content — without this a long release title pushes
+                 * the actions off the end at phone width. */
+                min-width: 0;
+                font-size: var(--yj-text-sm);
+                color: var(--yj-text-secondary, #b3b3b3);
+            }
+
+            .autotag-match-text strong {
+                color: var(--yj-text-primary, #fff);
+                font-weight: 600;
+            }
+
+            .autotag-match-note {
+                display: block;
+                margin-top: 2px;
+                font-size: var(--yj-text-xs);
+                color: var(--yj-text-tertiary, #888);
+            }
+
+            .autotag-match-actions {
+                display: flex;
+                align-items: center;
+                gap: 8px;
+                flex-shrink: 0;
+            }
+
             /* ── Other versions (a disclosure, below the tracklist) ── */
             .versions {
                 margin-top: 24px;
@@ -1062,6 +1130,14 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
         this.localTracks = [];
         this.filePaths = new Map();
         this.askedFor = new Set();
+        this.autotagMatch = null;
+
+        // Not awaited: the banner is a bonus and the page must not
+        // wait on it. It is also the *most* useful on an untagged
+        // album, which is exactly the page that has least else to
+        // show, so it is asked for on both branches below rather than
+        // only the catalog one.
+        void this.loadAutotagMatch();
 
         // Local-only album (no MBID) — populate entirely from library.
         if (!mbid && this.localAlbumId) {
@@ -1254,6 +1330,31 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
         return this.completeness;
     }
 
+    /**
+     * Ask whether the autotagger already has a confident match here.
+     *
+     * It answers from what the background prefetch has already scored
+     * and makes no MusicBrainz request, so this is safe on page load —
+     * see `MatchForAlbum`. A folder nobody has reached yet answers
+     * `null`, which is the same as "nothing to say": the banner is a
+     * bonus, so a failure is a missing suggestion rather than an error
+     * the user can act on, and it stays in the console.
+     */
+    private async loadAutotagMatch(): Promise<void> {
+        if (this.localAlbumId <= 0) {
+            this.autotagMatch = null;
+
+            return;
+        }
+
+        try {
+            this.autotagMatch = await MatchForAlbum(this.localAlbumId);
+        } catch (err) {
+            console.error('[explore-album] autotag match lookup failed', err);
+            this.autotagMatch = null;
+        }
+    }
+
     /**
      * Fetch and set `localTracks` directly by local album id — the
      * definite source of truth, used when nothing else has already
@@ -2415,6 +2516,7 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
                     entity-type="album"
                     @catalog-retry=${this.retryCatalog}
                 ></catalog-scope-notice>
+                ${this.renderAutotagMatch()}
                 ${this.renderChosenVersion()}
                 ${this.renderTracklistScope()}
                 ${this.renderTracklist()}
@@ -3069,6 +3171,155 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
 
     /* ── Version Selector (R025, R026, R027) ── */
 
+    /**
+     * "MusicBrainz has a match for this album."
+     *
+     * The complaint this answers is that the user had to notice the
+     * metadata was missing, then go and hunt the album down on the
+     * Autotag page — so the point is to say it *here*, while they are
+     * looking at the thing, with something to do about it.
+     *
+     * Three things about it are load-bearing.
+     *
+     * **Applying is offered only when it would do the whole album.** A
+     * tagging group is a folder, so a multi-disc album is several, and
+     * one button that applied to the best-scoring one would leave the
+     * album holding a mix of old and new tags — the exact case the
+     * app's Blocking notification level exists for. `groupCount` is
+     * the test, and the answer there is review, not apply.
+     *
+     * **The confirm is not a formality.** This rewrites tags on disk
+     * and cannot be undone, so it goes through `confirmAction()` with
+     * an impact line that says so in those words.
+     *
+     * **The banner does not claim a percentage.** The backend has a
+     * score and deliberately does not put it in the sentence: 0.95
+     * reads as a probability and is not one. What the user needs is
+     * which release it is, which is what the release title and artist
+     * are for.
+     */
+    private renderAutotagMatch() {
+        const match = this.autotagMatch;
+
+        if (!match) return nothing;
+
+        const wholeAlbum = match.groupCount === 1;
+
+        return html`
+            <div class="autotag-match" role="status">
+                <wa-icon name=${ICON_AUTOTAG} aria-hidden="true"></wa-icon>
+                <p class="autotag-match-text">
+                    MusicBrainz has a match for this album:
+                    <strong>${match.title}</strong>
+                    ${match.artistCredit ? html` by ${match.artistCredit}` : nothing}.
+                    ${wholeAlbum
+                        ? nothing
+                        : html`<span class="autotag-match-note"
+                              >It is filed as ${match.groupCount} folders here, so
+                              tagging it is a review rather than one
+                              step.</span
+                          >`}
+                </p>
+                <div class="autotag-match-actions">
+                    ${wholeAlbum
+                        ? html`<wa-button
+                              size="small"
+                              variant="brand"
+                              ?disabled=${this.applyingTags}
+                              @click=${this.onApplyAutotagMatch}
+                              >Apply tags</wa-button
+                          >`
+                        : nothing}
+                    <wa-button
+                        size="small"
+                        appearance="outlined"
+                        @click=${this.onReviewAutotagMatch}
+                        >Review in Autotag</wa-button
+                    >
+                </div>
+            </div>
+        `;
+    }
+
+    /** Hand the group over to the Autotag page and go there. */
+    private onReviewAutotagMatch = () => {
+        const match = this.autotagMatch;
+
+        if (!match) return;
+
+        this.dispatchEvent(
+            new CustomEvent('navigate', {
+                bubbles: true,
+                composed: true,
+                detail: { view: 'autotag', groupKey: match.groupKey },
+            }),
+        );
+    };
+
+    /**
+     * Apply the match, after asking.
+     *
+     * `ApplyAsync` is the registered-job path, so the work is visible
+     * in the jobs indicator and cancellable there like every other
+     * long-running operation — this page does not grow a second
+     * progress surface for it. What it does own is the *acknowledgement*
+     * that the request was accepted, because the button is here.
+     *
+     * The page is not refreshed on completion either: rewriting tags
+     * emits `TrackMetadataChanged`, which `library-store` answers by
+     * discarding every cached collection, and this page reloads from
+     * that like everything else.
+     */
+    private onApplyAutotagMatch = async () => {
+        const match = this.autotagMatch;
+
+        if (!match || this.applyingTags) return;
+
+        const ok = await confirmAction({
+            title: `Tag this album as “${match.title}”?`,
+            message:
+                `The ${match.trackCount} files of this album are rewritten to` +
+                ` match the MusicBrainz release${
+                    match.artistCredit ? ` by ${match.artistCredit}` : ''
+                }.`,
+            impact:
+                'This edits the tags in the files on disk and cannot be' +
+                ' undone. Nothing is moved or deleted.',
+            confirmLabel: 'Apply tags',
+        });
+
+        if (!ok) return;
+
+        this.applyingTags = true;
+
+        try {
+            await ApplyAsync(match.groupKey, match.releaseMbid);
+
+            // The suggestion has been acted on, so it stops being a
+            // suggestion immediately rather than sitting there inviting
+            // a second click while the job runs.
+            this.autotagMatch = null;
+
+            notificationStore.transient({
+                text: 'Tagging this album — progress is in the jobs indicator.',
+            });
+        } catch (err) {
+            console.error('[explore-album] autotag apply failed', err);
+
+            // Persistent rather than transient: the user asked for
+            // something that did not happen, and retrying is meaningful.
+            notificationStore.persistent({
+                text: describeError(
+                    err,
+                    'Those tags could not be applied.',
+                ),
+                tone: 'error',
+            });
+        } finally {
+            this.applyingTags = false;
+        }
+    };
+
     /**
      * Which pressing is on screen — said only when the user chose it.
      *

frontend/src/components/sidebar/app-sidebar.ts

@@ -6,6 +6,7 @@ import { designTokens } from '../../styles/tokens.css';
 import type { DragActiveDetail } from '@utils/drag-controller';
 import {
     ICON_PLAYLIST,
+    ICON_AUTOTAG,
     ICON_REQUESTED,
 } from '@utils/icon-language';
 
@@ -208,7 +209,7 @@ export class AppSidebar extends LitElement {
         { id: 'tracks', label: 'Tracks', icon: 'music' },
         { id: 'explore', label: 'Explore', icon: 'globe' },
         { id: 'downloads', label: 'Downloads', icon: ICON_REQUESTED },
-        { id: 'autotag', label: 'Autotag', icon: 'tag' },
+        { id: 'autotag', label: 'Autotag', icon: ICON_AUTOTAG },
         { id: 'jobs', label: 'Jobs', icon: 'list-check' },
         { id: 'settings', label: 'Settings', icon: 'gear' },
     ];