Preserve iPhone viewport lease across output stream churn

Packages/iOS/CmuxMobileShell/Sources/CmuxMobileShell/MobileShellComposite.swift

@@ -14776,7 +14776,11 @@ public final class MobileShellComposite: MobileTerminalOutputSinking {
         return streamToken
     }
 
-    private func unregisterTerminalOutput(surfaceID: String, streamToken: UUID) {
+    private func unregisterTerminalOutput(
+        surfaceID: String,
+        streamToken: UUID,
+        releaseViewport: Bool
+    ) {
         guard terminalOutputStreamTokensBySurfaceID[surfaceID] == streamToken else { return }
         terminalLatencyObserver.surfaceClosed(surfaceID: surfaceID)
         terminalLaneOutputReadySurfaceIDs.remove(surfaceID)
@@ -14833,8 +14837,13 @@ public final class MobileShellComposite: MobileTerminalOutputSinking {
             .terminalUnmounted,
             correlationID: surfaceID
         )
-        // Tell the Mac this device is no longer viewing the surface so it can unpin and clear its border.
-        clearTerminalViewport(surfaceID: surfaceID)
+        if releaseViewport {
+            // Ownerless and release-gate streams keep the historical contract:
+            // ending the stream means the viewer lease ended too. Mounted UI
+            // streams pass false here because UIKit/output-consumer churn is a
+            // narrower lifetime than presentation ownership.
+            clearTerminalViewport(surfaceID: surfaceID)
+        }
     }
 
     /// The output byte stream for a terminal surface.
@@ -14858,6 +14867,26 @@ public final class MobileShellComposite: MobileTerminalOutputSinking {
     public func terminalOutputStream(
         surfaceID: String,
         ownerID: UUID?
+    ) -> AsyncStream<MobileTerminalOutputChunk> {
+        terminalOutputStream(
+            surfaceID: surfaceID,
+            ownerID: ownerID,
+            releaseViewportOnTermination: true
+        )
+    }
+
+    /// Opens an owner-aware output stream with explicit viewport-lease
+    /// termination semantics.
+    ///
+    /// Mounted UIKit consumers set `releaseViewportOnTermination` to false:
+    /// their stream can end during a temporary window detach or bounded
+    /// consumer restart while the presentation still owns the sticky viewport
+    /// report. Presentation teardown releases that report explicitly through
+    /// `clearTerminalViewport(surfaceID:)`.
+    public func terminalOutputStream(
+        surfaceID: String,
+        ownerID: UUID?,
+        releaseViewportOnTermination: Bool
     ) -> AsyncStream<MobileTerminalOutputChunk> {
         AsyncStream { continuation in
             let streamToken = registerTerminalOutput(
@@ -14869,7 +14898,8 @@ public final class MobileShellComposite: MobileTerminalOutputSinking {
                 Task { @MainActor in
                     self?.unregisterTerminalOutput(
                         surfaceID: surfaceID,
-                        streamToken: streamToken
+                        streamToken: streamToken,
+                        releaseViewport: releaseViewportOnTermination
                     )
                 }
             }

Packages/iOS/CmuxMobileShellUI/Sources/CmuxMobileShellUI/GhosttySurfaceRepresentable.swift

@@ -513,9 +513,9 @@ struct GhosttySurfaceRepresentable: UIViewRepresentable {
                     }
                 }
             )
-            // Drive every output chunk into the libghostty surface. Ending this
-            // task terminates the stream, which unregisters the surface and
-            // clears its viewport pin on the Mac (see `terminalOutputStream`).
+            // Drive every output chunk into the libghostty surface. The output
+            // stream owns delivery only; this coordinator's presentation owns
+            // the sticky viewport lease and releases it explicitly on teardown.
             outputTaskGeneration &+= 1
             let taskGeneration = outputTaskGeneration
             let ownerID = UUID()
@@ -539,7 +539,8 @@ struct GhosttySurfaceRepresentable: UIViewRepresentable {
                 guard let store else { return }
                 for await chunk in store.terminalOutputStream(
                     surfaceID: surfaceID,
-                    ownerID: ownerID
+                    ownerID: ownerID,
+                    releaseViewportOnTermination: false
                 ) {
                     guard !Task.isCancelled else { return }
                     guard let self else { return }