There are a number of possible improvements to CodeContext.  They be separate issues (and PRs) that are dependencies of this master index issue. Some should be fairly easy now that we have the new tests.

1. #32831 added docstrings and tests.  Review has notes.
2. Follow-up may revise and do some user-invisible code cleanups.
3. #31493 cancelled the event loops when instances are deleted.
4. Spinoff from above: 1 or 2 events loops for class, not each instance.
5. #22703: separate initial context state of new window from toggling the state of current windows.  Current behavior is buggy.
6. Gray-out Options => Code Context on non-editor windows. (This would have to be revised again if windows became panes in master window.)
7. Change fixed # of lines to variable # of lines as needed, up to limit.  About 15 is limit for 4-space indents in 80 char lines. 
8. Click on context line jumps to line. Show it at top of window.
9. Reenable user config of context colors?
10. Somehow mark blocks in editor.  Subtle background color change?
Or tag just the indents, or, if add line numbers, the line numbers?