Tests: functional profile round-trip through the real main-window controls

Local checkpoint - NOT for public release.

Toward Ed's "every control and every function tested" goal: a new self-test applies a
profile to the ACTUAL main-window controls (via an internal ApplyThenCaptureForTest seam
on the headless form) and reads it straight back, asserting every persisted value
survived - volume, mute, send/receive toggles, peer-shaping master, send mode, send-all-
applications, and the selected applications. This exercises each control's load AND save
logic, not just that it exists (which the accessibility audit already covers).

The apply path pops the "set a password to stream" dialog when enabling send with no
password (would hang a headless test); the seam sets the existing suppressStreamingPasswordGate
around the apply, same gate the app uses internally.

Gate 25/25.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/MainForm.cs

@@ -8172,6 +8172,21 @@ public sealed class MainForm : Form
         return profile;
     }
 
+    /// <summary>Test-only: push a profile INTO the real controls and read it straight back OUT, so a
+    /// self-test can prove every persisted control both loads and saves correctly. Headless forms only
+    /// (a real form would try to reconnect peers etc.); pass a profile with no peers.</summary>
+    internal Profile ApplyThenCaptureForTest(Profile input)
+    {
+        pendingProfile = input;
+        settings.ApplyProfile(input);
+        // Suppress the interactive "set a password to stream" gate that a real user apply would show —
+        // it would pop a modal dialog and hang the headless test. We only care about control round-trip.
+        suppressStreamingPasswordGate = true;
+        try { ApplyPendingProfileToControls(); }
+        finally { suppressStreamingPasswordGate = false; }
+        return BuildCurrentProfile(input.Title);
+    }
+
     /// <summary>Common save body — gathers all current state into a Profile and writes it.
     /// On success, becomes the active profile (sets currentProfileTitle, updates window
     /// title, refreshes button visibility, and shows a confirmation popup).</summary>

src/RemSound.App/SelfTest.cs

@@ -75,6 +75,7 @@ internal static class SelfTest
         RunStep(results, "Bundled resources present", ResourcesPresent);
         RunStep(results, "Dialog accessibility (names + mnemonics)", AccessibilityAudit);
         RunStep(results, "Main window coverage (all tabs + controls)", MainWindowCoverage);
+        RunStep(results, "Main window profile round-trip (controls load + save)", MainWindowProfileRoundTrip);
 
         var failed = results.Count(r => r.Status == "FAIL");
         var skipped = results.Count(r => r.Status == "SKIP");
@@ -1050,6 +1051,53 @@ internal static class SelfTest
         finally { try { form.Dispose(); } catch { /* ignore */ } }
     }
 
+    /// <summary>Functional round-trip through the REAL main-window controls: apply a profile to the
+    /// controls, read it back, and assert every persisted value survived — proving each control's load
+    /// AND save logic, not just that it exists. Uses the headless form with no peers (so nothing tries
+    /// to connect). Device ticks need real hardware ids so they're covered by the profile-store
+    /// round-trip test instead; this covers the hardware-independent controls.</summary>
+    private static string? MainWindowProfileRoundTrip()
+    {
+        MainForm mf;
+        try { mf = new MainForm(null, RemSound.Core.Profile.NewBlank(), null, null, headless: true); }
+        catch (Exception ex) { return Skip($"headless MainForm could not be constructed: {ex.GetType().Name}: {ex.Message}"); }
+
+        using (mf)
+        {
+            var input = new Profile
+            {
+                Title = "roundtrip",
+                Volume = 42,
+                Muted = true,
+                ReceiveAudioOn = true,
+                SendAudioOn = true,
+                EnableAllPeerShaping = true,
+                WasapiSendMode = "applications",
+                SendAllApplications = false,
+            };
+            input.SelectedSendApplications.Add("vlc");
+            input.SelectedSendApplications.Add("firefox");
+
+            var back = mf.ApplyThenCaptureForTest(input);
+
+            Check(back.Volume == 42, $"volume must round-trip through the controls (got {back.Volume})");
+            Check(back.Muted, "mute must round-trip through the controls");
+            Check(back.ReceiveAudioOn && back.SendAudioOn, "send/receive toggles must round-trip");
+            Check(back.EnableAllPeerShaping, "the peer-shaping master switch must round-trip");
+
+            var covered = "volume, mute, send/receive, shaping";
+            if (RemSound.Sender.ProcessLoopbackCapture.IsSupported)
+            {
+                Check(back.WasapiSendMode == "applications", $"send mode must round-trip (got {back.WasapiSendMode})");
+                Check(!back.SendAllApplications, "the send-all-applications toggle must round-trip");
+                Check(back.SelectedSendApplications.Contains("vlc") && back.SelectedSendApplications.Contains("firefox"),
+                    "the selected applications must round-trip through the app list");
+                covered += ", send-mode, apps";
+            }
+            return $"round-tripped through the real controls: {covered}";
+        }
+    }
+
     private static int CountControls(Control root, Func<Control, bool> predicate)
     {
         var n = 0;