Fix iOS broadcast pump mapping churn

The screen-audio pump opened and disposed a memory mapping plus its container
lookup and path strings on every 5 ms tick - about 200 mapping pairs per
second of steady allocation that churned the GC under long calls. The producer
opens the ring with O_CREAT and never replaces it, so the pump now keeps one
mapping across ticks and rebuilds it only when the ring file disappears or a
drain fails.

tests/VoiceCat.Tests/PublishServerScriptTests.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Text.RegularExpressions;
 
 namespace VoiceCat.Tests;
 
@@ -117,6 +118,25 @@ public class PublishServerScriptTests
         Assert.DoesNotContain("if (OperatingSystem.IsIOSVersionAtLeast(27)) { model.ToggleScreenAudio();", settings);
     }
 
+    [Fact]
+    public async Task IosBroadcastPumpKeepsOneRingMappingAcrossTicks()
+    {
+        string root = FindRoot();
+        string pump = await File.ReadAllTextAsync(Path.Combine(
+            root, "clients", "apple", "VoiceCat.iOS", "BroadcastAudioPump.cs"));
+
+        // A mapping pair plus its container lookup and path strings per 5 ms tick allocated
+        // steadily at 200 Hz and churned the GC under long calls. The pump opens one mapping on
+        // the ring's transitions and reuses it; the producer never replaces the ring file.
+        Assert.Single(Regex.Matches(pump, "MemoryMappedFile.CreateFromFile"));
+        Assert.Contains("private bool OpenMapping()", pump);
+        Assert.Contains("private void CloseMapping()", pump);
+        Assert.Contains("Thread.Sleep(5)", pump);
+        Assert.Contains("File.Exists(path)", pump);
+        Assert.DoesNotContain("using MemoryMappedFile", pump);
+        Assert.DoesNotContain("using MemoryMappedViewAccessor", pump);
+    }
+
     [Fact]
     public async Task IosCaptureDoesNotDependOnCoalescedManagedTimers()
     {