Park the Watch run while iPhone edits an exercise or split

Publish an exclusive-edit lock (editingWorkoutID / editingSplitID) in the
phone→watch application context. While the phone has a workout's exercise
(ExerciseView) or a split (SplitDetailView) open in an editor, the watch pops
out of that run, blocks re-entry, and shows it as "Editing on iPhone" — so the
two devices never drive the same run at once and the watch can't clobber the
phone's edit with a stale optimistic write. The lock clears when the editor
closes; absent keys in the latest-wins context mean "not editing".

Claude-Session: https://claude.ai/code/session_01SCv7zvGFcKy47KSTnTLxRe

Workouts/Views/Splits/SplitDetailView.swift

@@ -12,6 +12,7 @@ import SwiftData
 
 struct SplitDetailView: View {
     @Environment(SyncEngine.self) private var sync
+    @Environment(AppServices.self) private var services
     @Environment(\.dismiss) private var dismiss
 
     var split: Split
@@ -109,6 +110,11 @@ struct SplitDetailView: View {
         } message: { item in
             Text("Remove \"\(item.name)\" from this split?")
         }
+        // Editing this split (or any of its exercises, all reached from here) parks any
+        // active watch run sourced from it — matched by splitID — so the watch can't keep
+        // performing an exercise whose plan we're reconfiguring.
+        .onAppear { services.watchBridge.setEditingSplit(split.id) }
+        .onDisappear { services.watchBridge.setEditingSplit(nil) }
     }
 
     private func moveExercises(from source: IndexSet, to destination: Int) {