perf: avoid eager diff loading and full-file typing work

tests/diff.rs

@@ -115,7 +115,7 @@ fn typed_diff_edits_unsaved_working_after_and_preserves_undo_on_explicit_close()
         session
             .editor()
             .diff()
-            .is_some_and(|diff| diff.phase == Phase::View)
+            .is_some_and(|diff| diff.phase == Phase::View && diff.selected_file_loaded())
     });
     let comparison = session
         .editor()
@@ -222,7 +222,7 @@ fn editable_diff_navigation_skips_omitted_lines_without_expanding_excerpts() {
         session
             .editor()
             .diff()
-            .is_some_and(|diff| diff.phase == Phase::View)
+            .is_some_and(|diff| diff.phase == Phase::View && diff.selected_file_loaded())
     });
     session.handle(Input::BackTab);
     let shown = |session: &EditorSession| {
@@ -350,7 +350,7 @@ fn readonly_jump_history_restores_the_comparison_file_and_source_cursor() {
         session.handle(input);
     }
     wait_until(&mut session, |session| {
-        session.editor().diff().unwrap().phase == Phase::View
+        session.editor().diff().unwrap().selected_file_loaded()
     });
     session.handle(Input::Char('\t'));
     let first_origin = session.editor().cursor();
@@ -365,6 +365,9 @@ fn readonly_jump_history_restores_the_comparison_file_and_source_cursor() {
     ] {
         session.handle(input);
     }
+    wait_until(&mut session, |session| {
+        session.editor().diff().unwrap().selected_file_loaded()
+    });
     let second_origin = session.editor().cursor();
     type_query(&mut session, "/second_before");
     session.handle(Input::Enter);