ADDITIONAL SYSTEM INFORMATION :
Debian 12.11
6.1.0-38-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.147-1 (2025-08-02) x86_64 GNU/Linux

Tested with similar results on multiple temurin Docker images, from eclipse-temurin:21-jdk (d6596e18495b) to :24-jdk.

A DESCRIPTION OF THE PROBLEM :
A switch expression involving sealed and non-sealed interfaces is not accepted by javac despite all possible cases being covered. As a workaround a redundant case can be appended in order to have the program compile.

In the demo code all Special instances are necessarily also Value instances, since SpecialValue is a Value and also the only permitted descendant of Special. Yet javac doesn't consider the Value case to cover Special.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the demo code with javac with no extra options.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code compiles without error.
ACTUAL -
Demo.java:12: error: the switch expression does not cover all possible input values
        return switch (base) {
               ^
1 error

---------- BEGIN SOURCE ----------
class Demo {

    sealed interface Base permits Special, Value {}

    non-sealed interface Value extends Base {}

    sealed interface Special extends Base permits SpecialValue {}

    non-sealed interface SpecialValue extends Value, Special {}

    static int demo(final Base base) {
        return switch (base) {
            case final Value value -> 0;
            // Uncommenting the following line will make javac accept this program
            //case final Special value -> throw new AssertionError();
        };

    }

}

---------- END SOURCE ----------