fix(mac): prevent Option release deadlock and HUD layout storm

The hold-to-talk release path called AsyncStream.Continuation.finish()
while holding MacAudioRecorder's NSLock; onTermination re-entered the
same lock on the main thread and froze the app. Finish snapshot sinks
outside the lock and guard the audio tap once stop() begins.

The dictation HUD no longer reassigns its hosting view and forces a
synchronous relayout on every view-model tick; it uses a fixed panel
size and SwiftUI @ObservedObject refresh instead.

Adds OSGKeyboardMacTests with a regression test that fails under the
old lock re-entry pattern.

OSGKeyboardMac/MacDictationOverlayView.swift

@@ -17,6 +17,22 @@ struct MacDictationOverlayView: View {
     var onResetPosition: (() -> Void)?
     @Environment(\.themePalette) private var palette
 
+    /// Pill body width. Wide enough for dot + live badge + a 320pt transcript
+    /// line + waveform + stop button at `Spacing.sm` gaps.
+    static let pillWidth: CGFloat = 500
+    /// Transparent margin around the pill, sized to contain the shadow's reach
+    /// (radius 14 + y 5). The panel is sized to pill + margin, and the shadow
+    /// would otherwise clip into hard translucent-black corners.
+    static let shadowMargin = EdgeInsets(top: 12, leading: 16, bottom: 20, trailing: 16)
+    /// Total panel size the hosting `NSPanel` should use.
+    static var panelSize: CGSize {
+        CGSize(
+            width: pillWidth + shadowMargin.leading + shadowMargin.trailing,
+            // 28pt content + 11pt vertical padding on each side.
+            height: 28 + 22 + shadowMargin.top + shadowMargin.bottom
+        )
+    }
+
     private var lang: AppUILanguage { viewModel.config.uiLanguage }
 
     private var isBusy: Bool {
@@ -46,19 +62,17 @@ struct MacDictationOverlayView: View {
         .frame(height: 28)
         .padding(.horizontal, Spacing.md)
         .padding(.vertical, 11)
-        .frame(minWidth: 300, idealWidth: 400, maxWidth: 520)
-        .fixedSize(horizontal: true, vertical: true)
+        // Fixed width, not intrinsic: the hosting panel is sized from this
+        // constant once, so a growing transcript never asks AppKit to resize
+        // the window mid-update. Long text truncates in `primaryLine` instead.
+        .frame(width: Self.pillWidth)
         .background(palette.surface, in: Capsule(style: .continuous))
         .overlay(
             Capsule(style: .continuous)
                 .stroke(palette.dividerStrong, lineWidth: 0.5)
         )
         .shadow(color: Color.black.opacity(0.22), radius: 14, y: 5)
-        // Transparent margin large enough to contain the shadow's reach
-        // (radius 14 + y 5). The panel is sized to `fittingSize`, which ignores
-        // shadow, so without this room the borderless window clips the shadow
-        // into hard translucent-black corners.
-        .padding(EdgeInsets(top: 12, leading: 16, bottom: 20, trailing: 16))
+        .padding(Self.shadowMargin)
         .contentShape(Capsule(style: .continuous))
         // Manual drag: `isMovableByWindowBackground` doesn't work on a
         // non-activating panel, so we move the panel ourselves. The controller