Extension: per-machine default tablet, skip asking unless busy

- Options page gains a 'Default tablet for this machine' picker,
  populated from the device list once base URL + terminal key are
  configured, auto-saved on change (small enough setting not to warrant
  its own Save button).
- Popup pre-selects the default in its device dropdown but still shows
  the full picker — opening the popup is already a deliberate action, so
  staff can still override it there.
- Injected buttons (row + banner) skip the dropdown entirely when a
  default is configured — one click pushes straight to it. Only falls
  back to the full picker if that specific push comes back busy (409),
  with a note explaining why it's asking despite a default being set.
  background.js's pushBooking() now returns the HTTP status alongside
  ok/error so this can be detected reliably rather than string-matching
  the error message.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/extension-src/content-script.js

@@ -89,14 +89,68 @@ function makeSendButton(bookingId, guestName, variant = 'block') {
   btn.addEventListener('click', e => {
     e.preventDefault();
     e.stopPropagation();
-    togglePanel(btn, bookingId, guestName, variant);
+    handleSendClick(btn, bookingId, guestName, variant);
   });
   return btn;
 }
 
+// Injected buttons skip asking which tablet entirely when a default is
+// configured for this machine (see options.js) — push straight to it. Only
+// falls back to the full device-picker panel if that specific push comes
+// back busy (409), or if no default is configured at all — see
+// project_checkin memory's extension notes, this was an explicit UX request
+// ("injected buttons don't need to ask which tablet, just use/send to
+// default unless busy"). The popup is deliberately different — it always
+// shows the picker, just pre-selected to the default (see popup.js) — since
+// opening the popup is already a more deliberate action than a one-click
+// inline button.
+async function handleSendClick(anchorBtn, bookingId, guestName, variant) {
+  const { defaultDeviceId } = await chrome.storage.local.get('defaultDeviceId');
+
+  if (defaultDeviceId) {
+    const status = showInlineStatus(anchorBtn, variant, 'Sending…');
+    const result = await chrome.runtime.sendMessage({
+      action: 'tcpPush', bookingId, deviceId: defaultDeviceId,
+    });
+    if (result?.ok) {
+      status.textContent = 'Sent — the tablet should navigate now.';
+      status.style.color = '#166534';
+      return;
+    }
+    if (result?.status === 409) {
+      status.remove();
+      // fall through to the picker below, with a note explaining why it's
+      // asking despite a default being configured
+      await togglePanel(anchorBtn, bookingId, guestName, variant, 'Default tablet is busy — choose another:');
+      return;
+    }
+    status.textContent = `Failed: ${result?.error || 'unknown error'}`;
+    status.style.color = '#dc2626';
+    return;
+  }
+
+  await togglePanel(anchorBtn, bookingId, guestName, variant);
+}
+
+// Small text-only status line for the default-tablet fast path — no
+// dropdown, nothing to pick, just feedback on what happened.
+function showInlineStatus(anchorBtn, variant, text) {
+  if (openPanel) { openPanel.remove(); openPanel = null; }
+  const el = document.createElement('div');
+  const width = variant === 'block' ? 'width: 100%;' : '';
+  el.style.cssText = `
+    display: block; margin-top: 6px; ${width} font-size: 12px; color: #64748b;
+    font-family: -apple-system, BlinkMacSystemFont, sans-serif;
+  `;
+  el.textContent = text;
+  anchorBtn.insertAdjacentElement('afterend', el);
+  openPanel = el;
+  return el;
+}
+
 let openPanel = null;
 
-async function togglePanel(anchorBtn, bookingId, guestName, variant = 'block') {
+async function togglePanel(anchorBtn, bookingId, guestName, variant = 'block', note = '') {
   if (openPanel) { openPanel.remove(); openPanel = null; }
 
   const panel = document.createElement('div');
@@ -111,7 +165,7 @@ async function togglePanel(anchorBtn, bookingId, guestName, variant = 'block') {
     font-family: -apple-system, BlinkMacSystemFont, sans-serif;
     font-size: 12px; color: #1e293b;
   `;
-  panel.textContent = 'Loading tablets…';
+  panel.textContent = note ? `${note} loading…` : 'Loading tablets…';
   anchorBtn.insertAdjacentElement('afterend', panel);
   openPanel = panel;
 
@@ -151,6 +205,12 @@ async function togglePanel(anchorBtn, bookingId, guestName, variant = 'block') {
   });
 
   panel.innerHTML = '';
+  if (note) {
+    const noteEl = document.createElement('div');
+    noteEl.textContent = note;
+    noteEl.style.cssText = 'margin-bottom: 6px; color: #b45309; font-weight: 600;';
+    panel.appendChild(noteEl);
+  }
   panel.appendChild(select);
   panel.appendChild(sendBtn);
 }