feat: the Discord Add panel's artist field autocompletes against FabledCurator's artists (milestone 429)

Operator, after the first live run: "I need the extension to offer an
autofill search function so it's easier to match an entry with an existing
artist."

- The field searches as soon as the panel opens (the server name, usually)
  and on every keystroke; matches list under it, with ↑/↓, Enter/Tab to pick,
  Esc to close, and a last "+ New artist" row.
- Inline autofill: the rest of the top match is filled in and selected, so
  typing on replaces it and Tab/Enter accepts it. Backspacing never refills.
- A result whose name IS the text, spacing and case aside, is picked on its
  own; the hint says in green which existing artist the source will join.
- /api/artists/autocomplete also matches ignoring spacing and punctuation
  ("Tamada Heijun" finds "TamadaHeijun"), ranked just below an exact match.
  The web UI's artist search gets it too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

extension/content/content-script.js

@@ -157,7 +157,6 @@
     closePanel();
     const d = probe.discord || {};
     const choice = discordPanelDefaults(probe);
-    let searchSeq = 0;
 
     const scopeRow = (value, label, disabled) => {
       const input = el('input', {
@@ -168,12 +167,21 @@
       return el('label', { class: 'fc-panel__radio' }, [input, el('span', { text: label })]);
     };
 
+    // The artist field is an autocomplete over FC's artists: it searches as
+    // soon as the panel opens (with the prefilled name) and on every keystroke,
+    // lists the matches under the field, fills in the rest of the top match as
+    // you type (Tab or Enter accepts it, typing on replaces it), and picks an
+    // artist whose name IS the text, spacing and case aside, without being
+    // asked. ↑/↓ walk the list; the last row creates a new artist instead.
     const nameInput = el('input', {
       type: 'text', class: 'fc-panel__input', value: choice.artistName,
-      placeholder: 'Artist name — search or type a new one',
+      placeholder: 'Search artists or type a new name',
       autocomplete: 'off', spellcheck: false,
+      role: 'combobox',
     });
-    const results = el('div', { class: 'fc-panel__results' });
+    nameInput.setAttribute('aria-autocomplete', 'both');
+    nameInput.setAttribute('aria-expanded', 'false');
+    const results = el('div', { class: 'fc-panel__results', role: 'listbox' });
     const hint = el('div', { class: 'fc-panel__hint' });
     const addBtn = el('button', { class: 'fc-panel__btn fc-panel__btn--primary', text: 'Add' });
     const cancelBtn = el('button', { class: 'fc-panel__btn', text: 'Cancel' });
@@ -185,41 +193,83 @@
       scopeRow('channel', d.channel_id ? channelLabel(d) : 'this channel', !d.channel_id),
       scopeRow('server', `Every channel in ${serverLabel(d)}`, false),
       el('div', { class: 'fc-panel__label', text: 'Artist' }),
-      nameInput,
-      results,
+      el('div', { class: 'fc-panel__combo' }, [nameInput, results]),
       hint,
       el('div', { class: 'fc-panel__actions' }, [cancelBtn, addBtn]),
     ]);
 
+    // Search state: the rows on screen, which one ↑/↓ has highlighted (-1 =
+    // none), and whether the list is open.
+    let rows = [];
+    let active = -1;
+    let listOpen = false;
+
     function refresh() {
       const req = discordAddRequest(choice);
       addBtn.disabled = !req;
       if (!req) hint.textContent = 'Pick an artist or type a name.';
-      else if (req.artistId != null) hint.textContent = `Connects to ${choice.artist.name} in FabledCurator.`;
-      else hint.textContent = `Adds to “${req.artistName}” — created if FabledCurator has no artist by that name.`;
+      else if (req.artistId != null) hint.textContent = `✓ Connects to ${choice.artist.name}, already in FabledCurator.`;
+      else hint.textContent = `Creates a new artist “${req.artistName}”.`;
+      hint.classList.toggle('fc-panel__hint--match', !!req && req.artistId != null);
     }
 
-    function showResults(rows) {
-      results.replaceChildren(...rows.map((a) => {
-        const row = el('button', { class: 'fc-panel__result', text: a.name });
-        row.addEventListener('click', () => {
-          choice.artist = { id: a.id, name: a.name };
-          choice.artistName = a.name;
-          nameInput.value = a.name;
-          results.replaceChildren();
-          refresh();
-        });
+    function pick(artist) {
+      choice.artist = artist ? { id: artist.id, name: artist.name } : null;
+      if (artist) {
+        choice.artistName = artist.name;
+        nameInput.value = artist.name;
+      }
+      closeList();
+      refresh();
+    }
+
+    function closeList() {
+      listOpen = false;
+      active = -1;
+      results.replaceChildren();
+      nameInput.setAttribute('aria-expanded', 'false');
+    }
+
+    function renderList() {
+      const typed = nameInput.value.trim();
+      const exact = exactArtistMatch(typed, rows);
+      const items = rows.map((a, i) => {
+        const row = el('button', { type: 'button', class: 'fc-panel__result', role: 'option' }, [
+          el('span', { text: a.name }),
+        ]);
+        if (choice.artist && choice.artist.id === a.id) {
+          row.appendChild(el('span', { class: 'fc-panel__result-tag', text: 'selected' }));
+        }
+        row.classList.toggle('fc-panel__result--active', i === active);
+        // mousedown, not click: it fires before the input's blur closes the list.
+        row.addEventListener('mousedown', (e) => { e.preventDefault(); pick(a); });
         return row;
-      }));
+      });
+      if (typed && !exact) {
+        const i = rows.length;
+        const create = el('button', { type: 'button', class: 'fc-panel__result fc-panel__result--new', role: 'option',
+          text: `+ New artist “${typed}”` });
+        create.classList.toggle('fc-panel__result--active', i === active);
+        create.addEventListener('mousedown', (e) => { e.preventDefault(); pick(null); choice.artistName = typed; refresh(); });
+        items.push(create);
+      }
+      if (typed && !rows.length) {
+        items.unshift(el('div', { class: 'fc-panel__empty', text: 'No FabledCurator artist matches.' }));
+      }
+      results.replaceChildren(...items);
+      listOpen = items.length > 0;
+      nameInput.setAttribute('aria-expanded', String(listOpen));
+      results.querySelector('.fc-panel__result--active')?.scrollIntoView({ block: 'nearest' });
     }
 
     let debounce = null;
-    nameInput.addEventListener('input', () => {
-      choice.artistName = nameInput.value;
-      refresh();
+    let searchSeq = 0;
+    // `autofill` is false for deletions: filling the name back in as you
+    // backspace would make it impossible to delete.
+    function search(autofill) {
       clearTimeout(debounce);
       const q = nameInput.value.trim();
-      if (!q) { results.replaceChildren(); return; }
+      if (!q) { rows = []; closeList(); return; }
       debounce = setTimeout(async () => {
         const mine = ++searchSeq;
         let r;
@@ -228,14 +278,69 @@
         } catch {
           return;
         }
-        if (mine !== searchSeq || r?.error) return;
-        showResults(r.artists || []);
-      }, 200);
+        // Stale: a later keystroke has its own search coming.
+        if (mine !== searchSeq || r?.error || nameInput.value.trim() !== q) return;
+        rows = r.artists || [];
+        active = -1;
+        const exact = exactArtistMatch(q, rows);
+        if (exact && !choice.artist) {
+          choice.artist = { id: exact.id, name: exact.name };
+        } else if (autofill && document.activeElement === nameInput) {
+          const hit = inlineCompletion(nameInput.value, rows);
+          const caret = nameInput.value.length;
+          if (hit && nameInput.selectionStart === caret) {
+            nameInput.value = nameInput.value + hit.name.slice(caret);
+            nameInput.setSelectionRange(caret, hit.name.length);
+            choice.artist = { id: hit.id, name: hit.name };
+            choice.artistName = hit.name;
+          }
+        }
+        renderList();
+        refresh();
+      }, 150);
+    }
+
+    nameInput.addEventListener('input', (e) => {
+      choice.artistName = nameInput.value;
+      // Any edit un-picks: the artist is whatever the field now says.
+      choice.artist = null;
+      refresh();
+      search(!String(e.inputType || '').startsWith('delete'));
     });
+    nameInput.addEventListener('focus', () => { if (rows.length) renderList(); });
+    nameInput.addEventListener('blur', () => closeList());
+
     // Keep Discord's global shortcuts from eating keystrokes meant for us.
     panel.addEventListener('keydown', (e) => {
       e.stopPropagation();
-      if (e.key === 'Escape') closePanel();
+      const count = results.querySelectorAll('.fc-panel__result').length;
+      if (e.target === nameInput && listOpen && count) {
+        if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
+          e.preventDefault();
+          active = e.key === 'ArrowDown' ? (active + 1) % count : (active <= 0 ? count - 1 : active - 1);
+          renderList();
+          return;
+        }
+        if ((e.key === 'Enter' || e.key === 'Tab') && active >= 0) {
+          e.preventDefault();
+          results.querySelectorAll('.fc-panel__result')[active]
+            .dispatchEvent(new MouseEvent('mousedown', { cancelable: true }));
+          return;
+        }
+        if ((e.key === 'Tab' || e.key === 'Enter') && choice.artist
+            && nameInput.selectionEnd > nameInput.selectionStart) {
+          // Accept the inline autofill — Enter too, but only to accept: the
+          // add itself takes a second Enter, once the hint names the artist.
+          e.preventDefault();
+          pick(choice.artist);
+          return;
+        }
+      }
+      if (e.key === 'Escape') {
+        if (listOpen) closeList();
+        else closePanel();
+        return;
+      }
       if (e.key === 'Enter' && e.target === nameInput && !addBtn.disabled) addBtn.click();
     });
 
@@ -253,6 +358,10 @@
     document.body.appendChild(panel);
     refresh();
     nameInput.focus();
+    nameInput.select();
+    // Search what the field opens with — the server's name, usually — so an
+    // artist it already matches is picked before the operator types anything.
+    if (!choice.artist && nameInput.value.trim()) search(false);
   }
 
   function showToast(text, kind) {