NEW ERROR AFTER FIX:

running 2 tests
test e2e_create_echo_box_and_return_string ... FAILED
test e2e_create_adder_box_and_return_sum ... FAILED

failures:

---- e2e_create_echo_box_and_return_string stdout ----
❌ Interpreter error: Return outside of function

thread 'e2e_create_echo_box_and_return_string' panicked at tests/e2e_plugin_echo.rs:102:33:
exec ok: ReturnOutsideFunction
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- e2e_create_adder_box_and_return_sum stdout ----
❌ Interpreter error: Return outside of function

thread 'e2e_create_adder_box_and_return_sum' panicked at tests/e2e_plugin_echo.rs:114:33:
exec ok: ReturnOutsideFunction


failures:
    e2e_create_adder_box_and_return_sum
    e2e_create_echo_box_and_return_string

test result: FAILED. 0 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.08s

PROGRESS: The Box types (EchoBox, AdderBox) are now recognized! 
The error changed from "Unknown Box type" to "Return outside of function".
This suggests the unified registry is working correctly after ChatGPT5's fix.