fix: show correct 'reach the Pi' URL per uplink mode + BUG-15

- Settings: when the Pi is on the phone's hotspot (mode phone), show the
  Pi's hotspot IP (http://<ip>) with an LTE-only hint instead of the AP URL
- BUG-15 documents the phone dual-role routing loop (host hotspot + connect
  to AP simultaneously breaks the uplink)

BUGS.md

@@ -8,7 +8,20 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
 
 ## Open bugs
 
-(No open bugs)
+### BUG-15 — Phone can't host the hotspot and connect to the Pi's AP at once
+- **Status**: `OPEN` 2026-08-12
+- **Symptom**: With the phone hosting the hotspot (Pi's uplink) *and* connected to the
+  Pi's AP ("vroom vroom yaris de course"), the Pi loses internet. Uploads fail with
+  `NameResolutionError` — the phone's WiFi-sharing routes the hotspot's traffic back
+  through the no-internet AP, creating a routing loop.
+- **Cause**: phone-OS limitation — a single phone can't cleanly be both the Pi's
+  internet uplink (AP/hotspot host) and its WiFi client (on the Pi's AP) simultaneously.
+- **Intended use / workaround**: phone must be **LTE-only** (WiFi off) to serve as the
+  Pi's uplink. Reach the Pi UI from that phone over the hotspot at
+  `http://<pi-hotspot-ip>` (Settings → "In-car hotspot" shows it), or from a second
+  device on the AP.
+- **Pi-side hardening shipped 2026-08-12**: `phone-hotspot` now forces public DNS
+  (`8.8.8.8`/`1.1.1.1`) and the Settings page surfaces the correct URL per uplink mode.
 
 ---
 

static/js/settings.js

@@ -302,22 +302,35 @@ async function loadUplinkStatus() {
 
         // In-car access card
         const hotspotInfo = document.getElementById('in-car-hotspot-info');
+        const phoneInfo = document.getElementById('in-car-phone-info');
         const wifiInfo = document.getElementById('in-car-wifi-info');
         const disconnectedInfo = document.getElementById('in-car-disconnected-info');
         const hotspotUrl = document.getElementById('hotspot-url');
+        const phoneUrl = document.getElementById('phone-url');
         const copyBtn = document.getElementById('copy-hotspot-url');
-        if (status.ap_active && status.ap_ip) {
+        const copyPhoneBtn = document.getElementById('copy-phone-url');
+        if (status.mode === 'phone' && status.ip_address) {
+            phoneUrl.textContent = `http://${status.ip_address}`;
+            hotspotInfo.hidden = true;
+            phoneInfo.hidden = false;
+            wifiInfo.hidden = true;
+            disconnectedInfo.hidden = true;
+            if (copyPhoneBtn) copyPhoneBtn.onclick = () => navigator.clipboard.writeText(`http://${status.ip_address}`);
+        } else if (status.ap_active && status.ap_ip) {
             hotspotUrl.textContent = `http://${status.ap_ip}`;
             hotspotInfo.hidden = false;
+            phoneInfo.hidden = true;
             wifiInfo.hidden = true;
             disconnectedInfo.hidden = true;
             if (copyBtn) copyBtn.onclick = () => navigator.clipboard.writeText(`http://${status.ap_ip}`);
-        } else if (status.mode === 'wifi' || status.mode === 'phone') {
+        } else if (status.mode === 'wifi') {
             hotspotInfo.hidden = true;
+            phoneInfo.hidden = true;
             wifiInfo.hidden = false;
             disconnectedInfo.hidden = true;
         } else {
             hotspotInfo.hidden = true;
+            phoneInfo.hidden = true;
             wifiInfo.hidden = true;
             disconnectedInfo.hidden = false;
         }

templates/settings.html

@@ -133,6 +133,19 @@
                     If the page doesn't load, try <strong>disabling cellular/mobile data</strong> on your phone.
                 </div>
             </div>
+            <div id="in-car-phone-info" hidden>
+                <p class="mb-2 fw-semibold">Your phone can reach the Pi at:</p>
+                <div class="d-flex align-items-center gap-2 mb-3">
+                    <code class="fs-5" id="phone-url">http://10.21.0.112</code>
+                    <button class="btn btn-outline-secondary btn-sm" id="copy-phone-url" type="button" title="Copy">
+                        <i class="fas fa-copy"></i>
+                    </button>
+                </div>
+                <div class="alert alert-info py-2 mb-0 small">
+                    <i class="fas fa-info-circle me-1"></i>
+                    The Pi is on your phone's hotspot. Keep the phone on <strong>mobile data (LTE)</strong> — don't also connect it to the Pi's WiFi.
+                </div>
+            </div>
             <div id="in-car-wifi-info" hidden>
                 <p class="mb-1 small text-muted">The Pi is connected to WiFi. Open <code>http://yaris.local</code> from any device on the same network.</p>
             </div>