chat: peer-switch strip, back button moved to flyout header

Switching conversations used to require bouncing back to the list view
and picking from there. Now the thread view has a horizontal peer
strip at the top: one click hops to another conversation, active tab
is highlighted and auto-scrolls into view, unread peers show a dot.
Scrollbar is hidden — vertical wheel delta is redirected to horizontal
scroll so the user can slide the strip with the mouse wheel when it
overflows.

In-thread header is gone; the back button moved next to "chat" in the
flyout header and only shows while a thread is open. Peer name stays
visible via the active tab.

Bumps to 1.9.3.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/plugins/chat/chat.js

@@ -142,6 +142,7 @@ function showListView() {
     $('chat-thread-view').classList.add('hidden');
     $('chat-pick-view').classList.add('hidden');
     $('chat-flyout-title').textContent = 'chat';
+    $('chat-header-back')?.classList.add('hidden');
     currentPeer = null;
 }
 
@@ -150,14 +151,17 @@ function showThreadView(peer) {
     $('chat-thread-view').classList.remove('hidden');
     $('chat-pick-view').classList.add('hidden');
     $('chat-flyout-title').textContent = 'chat';
-    $('chat-thread-peer').textContent = peer;
+    $('chat-header-back')?.classList.remove('hidden');
     currentPeer = peer;
+    // Re-render tabs so the active highlight follows the thread switch.
+    renderPeerTabs();
 }
 
 function showPickView() {
     $('chat-list-view').classList.add('hidden');
     $('chat-thread-view').classList.add('hidden');
     $('chat-pick-view').classList.remove('hidden');
+    $('chat-header-back')?.classList.add('hidden');
 }
 
 // ── Conversation list ─────────────────────────────────────────────
@@ -174,6 +178,7 @@ function renderConversations() {
     const list = $('chat-list');
     const empty = $('chat-empty');
     if (!list || !empty) return;
+    renderPeerTabs();
     if (!conversations.length) {
         list.innerHTML = '';
         empty.classList.remove('hidden');
@@ -205,6 +210,56 @@ function renderConversations() {
     });
 }
 
+// ── Peer tabs (thread-view quick-switch strip) ────────────────────
+// Horizontal row above the thread so the user can hop between
+// conversations without going back to the list. Hidden scrollbar;
+// vertical wheel delta is redirected to horizontal scroll.
+
+function renderPeerTabs() {
+    const strip = $('chat-thread-peers');
+    if (!strip) return;
+    // Fold the current peer in even if no messages exist yet (fresh
+    // pick-view selection), so switching back to it via tab is always
+    // possible.
+    const peers = conversations.slice();
+    if (currentPeer && !peers.some(c => c.peer === currentPeer)) {
+        peers.unshift({ peer: currentPeer, unread: 0 });
+    }
+    if (!peers.length) { strip.innerHTML = ''; return; }
+    strip.innerHTML = peers.map(c => {
+        const active = c.peer === currentPeer ? ' active' : '';
+        const dot = parseInt(c.unread) > 0 && c.peer !== currentPeer
+            ? '<span class="chat-peer-dot"></span>' : '';
+        return `<button class="chat-peer-tab${active}" data-peer="${escapeHtml(c.peer)}" title="${escapeHtml(c.peer)}">${dot}<span>${escapeHtml(c.peer)}</span></button>`;
+    }).join('');
+    strip.querySelectorAll('.chat-peer-tab').forEach(tab => {
+        tab.addEventListener('click', () => {
+            const peer = tab.dataset.peer;
+            if (peer && peer !== currentPeer) openConversation(peer);
+        });
+    });
+    // Keep the active tab in view after a switch so the user can see
+    // what's selected when the list overflows.
+    const active = strip.querySelector('.chat-peer-tab.active');
+    if (active) active.scrollIntoView({ block: 'nearest', inline: 'nearest' });
+}
+
+// Redirect vertical wheel scrolls to horizontal scroll on the peer
+// strip. Attached once on init — preventDefault only when we actually
+// consume the delta, so a trackpad user's native horizontal gesture
+// still works.
+function wirePeerStripWheel() {
+    const strip = $('chat-thread-peers');
+    if (!strip || strip.dataset.wheelWired) return;
+    strip.dataset.wheelWired = '1';
+    strip.addEventListener('wheel', (e) => {
+        if (e.deltaY === 0) return;
+        if (strip.scrollWidth <= strip.clientWidth) return;
+        e.preventDefault();
+        strip.scrollLeft += e.deltaY;
+    }, { passive: false });
+}
+
 // ── Thread ────────────────────────────────────────────────────────
 
 async function openConversation(peer) {
@@ -380,9 +435,10 @@ function init() {
     $('chat-refresh-btn').addEventListener('click', () => pollOnce().then(loadConversations));
     $('chat-new-btn').addEventListener('click', openPickView);
     $('chat-empty-start')?.addEventListener('click', openPickView);
-    $('chat-thread-back').addEventListener('click', () => { showListView(); loadConversations(); });
+    $('chat-header-back').addEventListener('click', () => { showListView(); loadConversations(); });
     $('chat-pick-back').addEventListener('click', showListView);
     $('chat-thread-form').addEventListener('submit', sendMessage);
+    wirePeerStripWheel();
 
     // Esc closes flyout when focus is inside it
     $('chat-flyout').addEventListener('keydown', e => {