fix(diffs): let the native layer own selection restore whenever it saved one

The ownership rule keyed on a deletions-side selection specifically, but the
native layer skips only the EDITABLE additions side. On a read-only diff with
Cmd+F find open, isEditable is false, so the native layer saved an
additions-side selection while the find-mode editor also restored its own --
both drove selection.

Key on whether a native selection exists at all, which is the actual invariant:
the native layer saves exactly what it intends to restore.

src/renderer/src/components/editor/pierre-diff/pierre-diff-edit-state.test.ts

@@ -74,7 +74,7 @@ it('reuses matching dormant document history and view state', () => {
   editor.finish()
 })
 
-it('yields selection restore to the native layer for a deletions-side selection', () => {
+it('yields selection restore to the native layer whenever it saved one', () => {
   const state = stored()
   states.set('native-owned', state)
   nativeViews.set('native-owned', { selection: { side: 'deletions' } })

src/renderer/src/components/editor/pierre-diff/pierre-diff-edit-state.ts

@@ -71,9 +71,10 @@ export const createPierreEditor: EditorFactory<PierreDiffAnnotationData, undefin
   // Pierre resumes an edited document only from a complete EditState; dropping diffSession
   // makes it rebuild and drop the restored selection. Keep it when the old side is unchanged,
   // otherwise fall back to fresh worker-computed hunks.
-  // Only one layer may drive selection. A saved deletions-side selection is restored natively,
-  // so hand the editor a rebuilt session there instead of letting it reassert its own.
-  const nativeOwnsSelection = getPierreNativeView(key)?.selection?.side === 'deletions'
+  // Only one layer may drive selection. The native layer saves exactly the selections it intends
+  // to restore (it skips the editable additions side), so any saved selection means it owns the
+  // restore and the editor must get a rebuilt session rather than reassert its own.
+  const nativeOwnsSelection = getPierreNativeView(key)?.selection != null
   const matchesOldSide =
     matchesContent &&
     !nativeOwnsSelection &&