Let the Device field be picked, not typed blind

Diagnosing capture on a real TV meant reading pactlSources off the
screen and typing an exact PulseAudio source name back in through the
same remote-driven text field — no way to copy-paste, easy to
mistype, and the one piece of information (which source, if any, is
actually RUNNING) was buried in a JSON dump.

Added two choice() pickers bound to the same capture.device setting:
one built from pactlSources (pulse/auto backends), one built from
alsaCapturePcms (alsa backend), both parsed from diagnostics the
service already collects — no new Luna method needed. Diagnostics
already run once at boot, so the picker is populated immediately,
before the user ever presses "Run diagnostics" by hand.

Picking a value writes straight into capture.device, and the plain
text field stays as the fallback for anything the parser misses.

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

frontend/js/app.js

@@ -188,6 +188,49 @@
     };
   }
 
+  // Typing a PulseAudio source name blind, off a diagnostics dump you can
+  // only read on the TV itself, is exactly the kind of thing a D-pad picker
+  // exists for. Parsed from the same "pactl list short sources" text that
+  // System > Run diagnostics already fetches — nothing new to ask the
+  // service for. Format is tab-separated: index, name, driver, sample_spec,
+  // state.
+  function pulseSourceOptions() {
+    var diag = state.diagnostics && state.diagnostics.system;
+    var text = diag && diag.pactlSources;
+    var out = [{ value: '', label: 'Automatic (@DEFAULT_MONITOR@)' }];
+    if (!text) {
+      return out;
+    }
+    text.split('\n').forEach(function (line) {
+      var cols = line.split('\t');
+      var name = cols[1];
+      if (!name) {
+        return;
+      }
+      var running = cols[4] ? ' — ' + cols[4] : '';
+      out.push({ value: name, label: name + running });
+    });
+    return out;
+  }
+
+  // alsaCapturePcms lines look like "00-01: ALC1220 Analog : ... : capture 1"
+  // — "00-01" is card 0, device 1, so hw:0,1. Best-effort: a line that does
+  // not start with that pattern is skipped rather than guessed at.
+  function alsaDeviceOptions() {
+    var diag = state.diagnostics && state.diagnostics.system;
+    var lines = (diag && diag.alsaCapturePcms) || [];
+    var out = [{ value: '', label: 'Automatic (default)' }];
+    lines.forEach(function (line) {
+      var m = /^(\d+)-(\d+):\s*(.*)$/.exec(line);
+      if (!m) {
+        return;
+      }
+      var hw = 'hw:' + parseInt(m[1], 10) + ',' + parseInt(m[2], 10);
+      out.push({ value: hw, label: hw + ' — ' + m[3] });
+    });
+    return out;
+  }
+
   var CAPTURE_FIELDS = [
     {
       path: 'capture.backend', label: 'Backend', type: 'choice',
@@ -199,7 +242,26 @@
       when: backendIs(['auto', 'pulse', 'alsa']),
       placeholder: 'blank = default monitor',
       hint: 'PulseAudio source name, or an ALSA PCM such as hw:0,0. '
-        + 'Run diagnostics to see what this TV has.',
+        + 'Run diagnostics, then use the picker below instead of typing.',
+    },
+    {
+      path: 'capture.device', label: 'Pick a discovered source', type: 'choice',
+      rebuild: true, wide: true,
+      when: function (s) {
+        return backendIs(['auto', 'pulse'])(s) && pulseSourceOptions().length > 1;
+      },
+      options: pulseSourceOptions,
+      hint: 'From the last diagnostics run. Press Enter to cycle through '
+        + 'every source this TV reported; picking one fills the Device field above.',
+    },
+    {
+      path: 'capture.device', label: 'Pick a discovered device', type: 'choice',
+      rebuild: true, wide: true,
+      when: function (s) {
+        return backendIs(['alsa'])(s) && alsaDeviceOptions().length > 1;
+      },
+      options: alsaDeviceOptions,
+      hint: 'From the last diagnostics run.',
     },
     {
       path: 'capture.server', label: 'PulseAudio server', type: 'text', wide: true,
@@ -714,6 +776,10 @@
 
   function runDiagnostics() {
     Luna.getDiagnostics(function (reply) {
+      state.diagnostics = reply;
+      // The Capture panel's device pickers are built from this same reply,
+      // so refresh it if that's the panel currently open.
+      renderCapture();
       var copy = JSON.parse(JSON.stringify(reply));
       delete copy.returnValue;
       showOutput(JSON.stringify(copy, null, 2));