The issue is minor, the scenarios below are only for users who change their option for a default editor (which can be done via the popup on some wikis).

• it's possible to switch from Add link surface to the source editor if a user has changed the default editor option, so Add link mode is not entirely isolated.
• in #1, "Edit source" tab flickers when a user clicks on "View history"

(1) if "Show me both editor tabs" is selected, the "Edit source" tab will be shown briefly when switching between tabs -"Edit", 'View history" and "Read"

• when hover the cursor changes to a hand icon implying that "Edit" tab is an active link (no effect though when clicking on it)
• from suggested Add link surface click on "View history", "Edit source" will momentarily displayed. On slow connection, it's possible to click on it.
• when "Edit source" is clicked, an article is displayed in the source editor with the Help panel properly prompting a user to switch to VE. The switching to VE works as expected - the suggested links are displayed.

(click to animate the gif)

(2) if "Always give me the source editor" is selected, then clicking on "Edit" tab from Add link suggested mode will bring "Edit source" mode. The Help panel will display the suggestion to switch back to VE.