Fix BidirectionalRelay half-close handling - #41328

src/windows/common/relay.cpp:323

• With the loop now exiting only when both handles are null, hitting EOF on one side (where the code sets LeftHandle = nullptr / RightHandle = nullptr) causes the relay to keep reading from the other side but skip the corresponding write (else if (RightHandle != nullptr) / else if (LeftHandle != nullptr)), effectively dropping data rather than draining it. To support TCP half-close correctly, consider tracking read-EOF state separately (e.g., leftReadClosed/rightReadClosed) while keeping the HANDLE for writes, and only stopping writes on actual write failure.

        if ((LeftHandle == nullptr) && (RightHandle == nullptr))
        {
            break;
        }

src/windows/common/relay.cpp:301

• BidirectionalRelay is declared with _In_ HANDLE LeftHandle/RightHandle (non-null), and current call sites pass non-null handles. Initializing leftReadClosed/rightReadClosed from == nullptr is therefore redundant/misleading; either assert the non-null contract here or (if nullptr is valid) the API should be _In_opt_ and documented accordingly.

    bool leftReadClosed = (LeftHandle == nullptr);
    bool rightReadClosed = (RightHandle == nullptr);