Mac in the headset: a Show waits for a viewer cleanup already in progress

Review round 11: the cleanup's check and pkill now hold a lock that Show
takes to count itself in, so a new viewer can't start between them.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ui/frame_macview.py

@@ -130,6 +130,9 @@ class MacView:
         self.closing = False
         self.shows = 0  # counts Show presses, so a late cleanup can't close a new viewer
         self.launching = 0  # Shows in progress (one may be replacing its own stream)
+        # Held by a Show while it counts itself in, and by the cleanup for its
+        # check and its pkill together, so a Show can't start in between.
+        self.viewer_lock = threading.Lock()
         self.shown = set()  # sources with a viewer out there, connected or retrying
         self.browser_flags = list(BROWSER_FLAGS)
 
@@ -281,12 +284,12 @@ class MacView:
     # ---- viewers on the Frame ----
 
     def show(self, src, quality="balanced", width=None, height=None):
-        with self.lock:
+        with self.viewer_lock:
             self.launching += 1
         try:
             return self._show(src, quality, width, height)
         finally:
-            with self.lock:
+            with self.viewer_lock:
                 self.launching -= 1
 
     def _show(self, src, quality, width, height):
@@ -347,12 +350,13 @@ class MacView:
         2026-09-28), so once nothing is shown, end it. It runs with a profile
         of its own, so nothing else is touched."""
         time.sleep(2)  # the viewers close their windows first
-        if self.shown or self.shows != shows or self.launching:
-            return
-        try:
-            self.run("pkill -f '[f]rame-control/mac-view|[d]ata/frame-mac-view' || true", timeout=10)
-        except Exception:
-            pass
+        with self.viewer_lock:
+            if self.shown or self.shows != shows or self.launching:
+                return
+            try:
+                self.run("pkill -f '[f]rame-control/mac-view|[d]ata/frame-mac-view' || true", timeout=10)
+            except Exception:
+                pass
 
     def state(self):
         reason = self.unavailable()