$ java -cp old Client     (Client and Shape compiled together, v1)     (25.0.4.1+1-LTS)
circle: 3.141592653589793
square: 4.0

$ java -cp new:old Main     (Shape gained Triangle; Client.class NOT recompiled)     (25.0.4.1+1-LTS)
Exception in thread "main" java.lang.MatchException
	at Client.area(Client.java:4)
	at Main.main(Main.java:4)

$ javac -cp new sep/client/Client.java     (now recompile Client against v2)     (25.0.4.1+1-LTS)
sep/client/Client.java:4: error: the switch expression does not cover all possible input values
        return switch (s) {
               ^
1 error

$ java -cp old Client     (Client and Shape compiled together, v1)     (27+35)
circle: 3.141592653589793
square: 4.0

$ java -cp new:old Main     (Shape gained Triangle; Client.class NOT recompiled)     (27+35)
Exception in thread "main" java.lang.MatchException
	at Client.area(Client.java:4)
	at Main.main(Main.java:4)

$ javac -cp new sep/client/Client.java     (now recompile Client against v2)     (27+35)
sep/client/Client.java:4: error: the switch expression does not cover all possible input values
        return switch (s) {
               ^
  missing patterns:
      Triangle _
1 error