Account zone is world-independent: avatar stays in Record world

Creator on the live build: 'why do you make the youtube user icon go away?'
The TASK 42 one-surface bar had scoped the account zone to Stream only
('Record world has no YouTube identity at all'), so arming REC dropped the
avatar and the bar height bounced with it ('really fucking annoying').

Fix: ShowSignInButton / ShowAvatarButton are now plain !IsConnected /
IsConnected — app-level identity, present in both worlds, so the right
column never pops in/out and the bar height stays pinned. Test remains a
child of Stream (still stream-armed AND signed-in).

TopBarModeTests updated to the new contract: signed-out Record world shows
Sign In; flipping back to REC keeps the avatar. PillRadioTests untouched
(it only exercises the ON-AIR face). Docs corrected in-place (ai.md state
model, TASK 42 scope). Gate: clean build 0-warnings, 316/316, scope passed.

ytLive.Tests/TopBarModeTests.cs

@@ -10,11 +10,12 @@ namespace ytLive.Tests;
 
 /// <summary>
 /// Top bar redesign — the bar is ONE surface rendered by the FIRST decision
-/// (Record or Stream). Each world is the whole bar: the Record world has no
-/// YouTube identity at all, the Stream world owns the account zone (Sign In or
-/// avatar) plus Test. The switch is a two-position gate, so "going back" is one
-/// tap on the other segment. While running, the switch retires and a single
-/// reality line (dot + word + elapsed) + End replace it.
+/// (Record or Stream). Each world is the whole bar: Test is a child of Stream,
+/// but the account zone (Sign In / avatar) is WORLD-INDEPENDENT (creator
+/// 2026-09-23) so the right column never pops in and out and the bar height
+/// stays pinned. The switch is a two-position gate, so "going back" is one tap
+/// on the other segment. While running, the switch retires and a single reality
+/// line (dot + word + elapsed) + End replace it.
 /// </summary>
 [Collection("RealApp")]
 public sealed class TopBarModeTests
@@ -45,11 +46,12 @@ public sealed class TopBarModeTests
             vm.IsConnected = false;
 
             // Default (nothing armed) = the Record world: Go says "Start Recording",
-            // no account zone, no Test — YouTube doesn't exist in this world.
+            // no Test — but the account zone is app-level and stays (signed out →
+            // Sign In visible even here; no avatar).
             Assert.True(vm.ShowIdleWorld);
             Assert.True(vm.ShowRecordAction);
             Assert.False(vm.ShowStreamActions);
-            Assert.False(vm.ShowSignInButton);
+            Assert.True(vm.ShowSignInButton);
             Assert.False(vm.ShowAvatarButton);
             Assert.False(vm.ShowTestButton);
             Assert.Equal("Start Recording", vm.PrimaryStartButtonLabel);
@@ -72,11 +74,12 @@ public sealed class TopBarModeTests
             Assert.True(vm.ShowAvatarButton);
             Assert.True(vm.ShowTestButton);
 
-            // Going back is one tap: flipping REC returns the bar to the Record world.
+            // Going back is one tap: flipping REC returns the bar to the Record world —
+            // the avatar STAYS (world-independent account zone), only Test retires.
             vm.RecordPillOn = true;
             Assert.False(vm.ShowStreamActions);
             Assert.True(vm.ShowRecordAction);
-            Assert.False(vm.ShowAvatarButton);
+            Assert.True(vm.ShowAvatarButton);
             Assert.False(vm.ShowTestButton);
             Assert.Equal("Start Recording", vm.PrimaryStartButtonLabel);